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Thread: Everything about everything ....almost (long thread)

  1. #1
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    Everything about everything ....almost (long thread)

    Table of Contents
    *****************

    1 Definitions
    1.1 What do all of those acronyms mean?
    1.2 What is meant by "frequency response?"
    1.3 What is a "soundstage?" What is an "image?"
    1.4 What is meant by "anechoic?"
    2 Electrical
    2.1 My speakers make this high-pitched whine which matches the engine's
    RPMs. What is it, and how can I get rid of it?
    2.1.1 Level 1: Check out the Amplifier(s)
    2.1.2 Level 2: Reduce the System
    2.1.3 Level 3: Move the Head Unit
    2.1.4 Level 4: Testing the Car
    2.1.5 Level 5: Adding Signal Processors
    2.1.6 Level 6: Processor Isolation Tests
    2.2 My system "pops" when I turn it off. What is happening and how
    can I get rid of it?
    2.3 What is the best power wire to use?
    2.4 What is the best speaker wire to use?
    2.5 I heard that I should run my power wire directly to my car's
    battery. Why should I bother, and how do I do it?
    2.6 Should I do the same thing with my ground wire, then?
    2.7 Sometimes when I step out of my car, I get a really bad shock.
    What is wrong with my system?
    2.8 When my car is running and I have the music turned up loud,
    my headlights dim with the music. Do I need a new battery or
    a new alternator?
    2.9 What is a "stiffening capacitor", and how does it work?
    2.10 Should I install one in my car? If so, how big should it be,
    and where do I get one?
    2.11 What about adding a new battery? Or upgrading the amplifier?
    3 Components
    3.1 What do all of those specifications on speakers mean?
    3.2 Are component/separates any better than fullrange or coaxials?
    3.3 What are some good (and bad) brands of speakers?
    3.4 What do all of those specifications on amplifiers mean?
    3.5 What does "bridging an amp" mean?
    3.5.1 Why should I bridge my amp?
    3.5.2 Why shouldn't I bridge my amp?
    3.5.3 What happens when an amp is bridged?
    3.5.4 Does bridging an amp would halve the impedance of the speakers?
    3.5.5 Can I bridge my 4 channel head unit?
    3.6 What is "mixed-mono?" Can my amp do it?
    3.7 What does "two ohm stable" mean? What is a "high-current" amplifier?
    3.8 Should I buy a two or four (or more) channel amplifier?
    3.9 What are some good (and bad) brands of amplifiers?
    3.10 What is a crossover? Why would I need one?
    3.11 Should I get an active or a passive crossover?
    3.12 Should I buy an equalizer?
    3.13 What are some good (and bad) brands of equalizers?
    3.14 What do all of those specifications on tape deck head units
    mean?
    3.15 What are features to look for in a tape deck?
    3.16 What are some good (and bad) brands of tape decks?
    3.17 What are features to look for in a CD head unit?
    3.18 Should I buy a detachable faceplate or pullout CD player?
    3.19 What are some good (and bad) brands of CD head units?
    3.20 Can I use my portable CD player in my car? Won't it skip a lot?
    3.21 What's that weird motor noise I get with my portable CD player?
    3.22 What are some good (and bad) brands of portable CD players?
    3.23 What's in store for car audio with respect to MD, DAT and DCC?
    3.24 Are those FM modulator CD changers any good? What are my other
    options?
    3.25 What kind of changer will work with my factory head unit?
    3.26 What are some good (and bad) brands of CD changers?
    3.27 Why do I need a center channel in my car, and how do I do it?
    3.28 Should I buy a sound field processor?
    3.29 What are some good (and bad) brands of signal processors?
    3.30 I keep hearing that speakers for Company X are made by Company
    Y. What's the deal?
    3.31 What is a Line Driver? Do I need one?
    3.32 Can I play MP3 files in my car?
    4 Subwoofers
    4.1 What are "Thiele/Small parameters?"
    4.2 How does speaker sensitivity affect real world SPL? Will a higher
    sensitivity give me a larger SPL?
    4.3 What are the enclosure types available?
    4.4 Which enclosure type is right for me?
    4.4.1 Infinite Baffle ("free-air")
    4.4.2 Sealed Box
    4.4.3 Ported Box
    4.4.4 Bandpass Box
    4.5 How do I build an enclosure?
    4.6 MDF for Dummies
    4.6.1 What is MDF?
    4.6.2 Where can I get MDF?
    4.6.3 What type of saw blade works best when cutting MDF?
    4.6.4 What type of router bits work well with MDF?
    4.7 What driver should I use?
    4.8 Is there any computer software available to help me choose an
    enclosure and a driver?
    4.9 What is an "aperiodic membrane?"
    4.10 Can I use my subs in the winter?
    4.11 How can I carpet my enclosure?
    4.12 Are large magnets always better than small magnets?
    4.13 I know the box volume required for my subwoofer, but what are
    the best dimensions for my enclosure?
    5 Installation
    5.1 Where should I buy the components I want?
    5.2 What mail-order companies are out there?
    5.3 What tools should I have in order to do a good installation?
    5.4 Where should I mount my speakers?
    5.5 What is "rear fill", and how do I effectively use it?
    5.6 How do I set the gains on my amp?
    5.7 How do I select proper crossover points and slopes?
    5.8 How do I flatten my system's frequency response curve?
    5.9 How do I wire speakers "in series" and "in parallel?"
    5.10 Are there any alternatives for Dynamat? It's too expensive!
    5.11 How many devices can I attach to my remote turn-on lead?
    5.12 How do I wire a relay in my system?
    5.13 How do I design my own passive crossovers?
    5.14 How do I build my own passive crossovers?
    5.15 Can I split the single pre-amp output from my head unit to drive
    two amplifiers with a Y-cable?
    5.16 How do I turn a stereo signal into a mono signal
    5.17 How do I determine a speaker's polarity?
    5.18 How can I use an oscilloscope to set the gains in my system?
    5.19 Why are kickpanels such a popular location for mounting speakers?
    5.20 How can I build custom kickpanels?
    5.21 What's worse for a speaker, too much or too little power?
    5.22 Why is distortion harmful to my speakers?
    5.23 What tools do I need to cut Plexiglas?
    5.24 Are there any other special requirements for working with Plexiglas?
    6 Competition
    6.1 What is IASCA, and how do I get involved?
    6.2 What is USAC, and how do I get involved?
    6.3 What are the competitions like?
    6.4 Should I compete?
    6.5 What class am I in?
    6.6 Where can I find out when these Sound-Offs are?
    6.7 How do I get sponsored by a manufacturer?
    7 Literature
    7.1 What magazines are good for car audio enthusiasts?
    7.2 Are there any newsletters I can read?
    7.3 What books can I read?
    7.4 Can I contact any manufacturers on-line?
    Last edited by one; 01-15-2004 at 06:36 PM.
    Smell that? ......German leather and palm sweat.

  2. #2
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    1 Definitions
    ******************

    This section contains background information which defines some of the
    acronyms and terminology commonly used in the car audio world.
    Understanding these definitions is important in order to understand the
    other sections of this document.


    1.1 What do all of those acronyms mean? [JSC]
    ================================================

    `A' is for "amperes", which is a measurement of current equal to one
    coulomb of charge per second. You usually speak of positive current -
    current which flows from the more positive potential to the more
    negative potential, with respect to some reference point (usually
    ground, which is designated as zero potential). The electrons in a
    circuit flow in the opposite direction as the current itself. Ampere
    is commonly abbreviated as "amp", not to be confused with amplifiers, of
    course, which are also commonly abbreviated "amp". In computation, the
    abbreviation for amps is commonly "I".

    `V' is for "volts", which is a measurement of electric potential.
    Voltages don't "go" or "move", they simply exist as a measurement (like
    saying that there is one mile between you and some other point).

    `DC' is for "direct current", which is a type of circuit. In a DC
    circuit, all of the current always flows in one direction, and so it is
    important to understand which points are at a high potential and which
    points are at a low potential. For example, cars are typically 12VDC
    (twelve volts direct current) systems, and it is important to keep
    track of which wires in a circuit are attached to the +12V (positive
    twelve volts) lead of the battery, and which wires are attached to the
    ground (or "negative") lead of the battery. In reality, car batteries
    tend to have a potential difference of slightly higher than 12V, and
    the charging system can produce upwards of 14.5V when the engine is
    running.

    `AC' is for "alternating current", which is a type of circuit in which
    the voltage potential fluctuates so that current can flow in either
    direction through the circuit. In an AC circuit, it is typically not
    as important to keep track of which lead is which, which is why you can
    plug household appliances into an outlet the "wrong way" and still have
    a functioning device. The speaker portions of an audio system comprise
    an AC circuit. In certain situations, it is indeed important to
    understand which lead is "positive" and which lead is "negative"
    (although these are just reference terms and not technically correct).
    See below for examples. The voltage of an AC circuit is usually given
    as the RMS (root mean square) voltage, which, for sinusoidal waves, is
    simply the peak voltage divided by the square root of two.

    `W' is for "watts", a measurement of electrical power. One watt is
    equal to one volt times one amp, or one joule of energy per second. In
    a DC circuit, the power is calculated as the voltage times the current
    (P=V x I). In an AC circuit, the RMS power is calculated as the RMS
    voltage times the RMS current (Prms=Vrms x Irms).

    `Hz' is for "hertz", a measurement of frequency. One hertz is equal to
    one inverse second (1/s); that is, one cycle per second, where a cycle
    is the duration between similar portions of a wave (between two peaks,
    for instance). Frequency can describe both electrical circuits and
    sound waves, and sometimes both. For example, if an electrical signal
    in a speaker circuit is going through one thousand cycles per second
    (1000Hz, or 1kHz), the speaker will resonate at 1kHz, producing a 1kHz
    sound wave. The standard range of human hearing is "twenty to twenty",
    or 20Hz-20kHz, which is three decades (three tenfold changes in
    frequency) or a little under ten octaves (ten twofold changes in
    frequency).

    `dB' is for "decibel", and is a measurement for power ratios. To
    measure dB, you must always measure with respect to something else.
    The formula for determining these ratios is P=10^(dB/10), which can be
    rewritten as dB=10log(P). For example, to gain 3dB of output compared
    to your current output, you must change your current power by a factor
    of 10^(3/10) = 10^0.3 = 2.00 (that is, double your power). The other
    way around, if you triple your power (say, from 20W to 60W) and want to
    know the corresponding change in dB, it is dB=10log(60/20)=4.77 (that
    is, an increase of 4.77dB). If you know your logarithms, you know that
    a negative number simply inverts your answer, so that 3dB corresponding
    to double power is the same as -3dB corresponding to half power. There
    are several other dB formulas; for instance, the voltage measurement is
    dB=20log(V). For example, a doubling of voltage produces 20log2 =
    6.0dB more output, which makes sense since power is proportional to the
    square of voltage, so a doubling in voltage produces a quadrupling in
    power.

    `SPL' is for "sound pressure level" and is similar to dB. SPL
    measurements are also ratios, but are always measured relative to a
    constant. This constant is 0dB which is defined as the smallest level
    of sound pressure that the human ear can detect. 0dB is equal to
    10^-12 (ten to the negative twelfth power) W/m^2 (watts per square
    meter). As such, when a speaker is rated to produce 92dB at 1m when
    given 1W (92dB/Wm), you know that they mean that it is 92dB louder than
    10^-12W/m^2. You also know than if you double the power (from 1W to
    2W), you add 3dB, so it will produce 95dB at 1m with 2W, 98dB at 1m with
    4W, 101dB at 1m with 8W, etc.

    `THD' is for "total harmonic distortion", and is a measure of the how
    much a certain device may distort a signal. These figures are usually
    given as percentages. It is believed that THD figures below
    approximately 0.1% are inaudible. However, it should be realized that
    distortion adds, so that if a head unit, equalizer, signal processor,
    crossover, amplifier and speaker are all rated at "no greater than
    0.1%THD", together, they could produce 0.6%THD, which could be
    noticeable in the output.

    An "Ohm" is a measure of resistance and impedance, which tells you how
    much a device will resist the flow of current in a circuit. For
    example, if the same signal at the same voltage is sent into two
    speakers - one of which is nominally rated at 4 ohms of impedance, the
    other at 8 ohms impedance - twice as much current will flow through the
    4 ohm speaker as the 8 ohm speaker, which requires twice as much power,
    since power is proportional to current.


    1.2 What is meant by "frequency response?" [JSC]
    ================================================== =

    The frequency response of a device is the range of frequencies over
    which that device can perform in some fashion. The action is specific
    to the device in question. For example, the frequency response of the
    human ear is around 20Hz-20kHz, which is the range of frequencies which
    can be resolved by the eardrum. The frequency response of an amplifier
    may be 50Hz-40kHz, and that of a certain speaker may be 120Hz-17kHz.
    In the car audio world, frequency responses should usually be given
    with a power ratio range as well, such as (in the case of the speaker)
    120Hz-17kHz +/-3dB. What this means is that given an input signal
    anywhere from 120Hz to 17kHz, the output signal is guaranteed to be
    within an "envelope" that is 6dB tall. Typically the extreme ends of
    the frequency range are the hardest to reproduce, so in this example,
    the 120Hz and 17kHz points may be referred to as the "-3dB points" of
    the amplifier. When no dB range is given with a frequency response
    specification, it can sometimes be assumed to be +/-3dB.


    1.3 What is a "soundstage?" What is an "image?" [CD]
    ================================================== =====

    The "soundstage" is the position (front/back and high/low) that the
    music appears to be coming from, as well as the depth of the stage. A
    car with speakers only in the front will likely have a forward
    soundstage, but may not have enough rear fill to make the music seem
    live. A car with both front and rear speakers may have anything from a
    forward to a rear soundstage, with an accompanying fill from the softer
    drivers depending on the relative power levels and the frequencies
    reproduced. The high/low position of the soundstage is generally only
    obvious in a car with a forward soundstage. The music may seem to be
    originating in the footwells, the dash, or out on the hood, depending
    on how the drivers interact with the environment.

    The "stereo image" is the width and definition of the soundstage.
    Instruments should appear to be coming from their correct positions,
    relative to the recording. The position of the instruments should be
    solid and easily identifiable, not changing with varying frequencies.
    A car can image perfectly with only a center-mounted mono speaker, but
    the stereo placement of the music will be absent.


    1.4 What is meant by "anechoic?" [JSC]
    =========================================

    "Anechoic" means not echoing. It usually refers to a style of
    measuring a speaker's output which attempts to eliminate echoes (or
    "reflections") of the speaker's output back to the measurement area,
    which could alter the measurement (positively or negatively).


    2 Electrical
    *****************

    This section describes various problems and concepts which are closely
    related to electronics.


    2.1 My speakers make this high-pitched whine which matches the engine's
    RPMs. What is it, and how can I get rid of it? [IDB]
    ================================================== ========================

    The answer to this section was generously provided by David Navone of
    Autosound 2000. The material in these instructions was adapted from
    the Autosound 2000 Troubleshooting Flow Chart by Ian Bjorhovde with the
    permission of Autosound 2000. For more information about Autosound
    2000, (see Section 7).

    This is a set of instructions to debug a stereo installation if there
    is any noise present after it is completed. Follow each step
    carefully! If you have more than one amplifier, repeat level one for
    each amp to be sure that none of them are responsible for the noise.


    2.1.1 Level 1: Check out the Amplifier(s)
    ------------------------------------------

    After you have determined that there is noise in the system, determine
    if the amplifier is causing the noise. To do this, mute the signal at
    the inputs to the amp by using shorting plugs. If there is no noise,
    then the amp is fine, and you can proceed to level 2. However, if
    there is noise, then use a test speaker at the amp's output. If this
    stops the noise, then the problem is originating in the speaker wiring,
    or the passive crossovers. Check to make sure that none of these are
    shorting with the body of the car, and start again at level 1. If
    noise is still present when using the test speaker, then there may be a
    problem with the power supply on the amp. Try connecting an isolated
    power supply - if this does not get rid of the noise, then there is
    something seriously wrong with the amp, and it should be replaced. If
    the noise goes away, then there may be a problem with power supply
    filtering or isolation. This can be fixed by changing the amp's ground
    point or b adding external supply filtering.


    2.1.2 Level 2: Reduce the System
    ---------------------------------

    The amps have been determined to be noise free. If you have any
    processors between the head unit and the amps, disconnect them and
    connect the head unit directly to the amp. If this gets rid of the
    noise, then one (or more) of the processors must be at fault, so
    proceed to level 5. Otherwise, try running the signal cables over a
    number of different routes. If you are able to find one that does not
    produce any noise, permanently route the cables in the same manner, and
    proceed to level 5. If not, then you must isolate the head unit from
    the car's chassis (except for its ground!) - don't forget to disconnect
    the antenna, since it is also grounded to the car. If isolating
    the head unit does not solve the problem, the move the grounding point
    of the head unit. Hopefully the noise will be gone, and you can
    install the head unit with a quiet ground and proceed to level 5,
    otherwise go on to level 3.


    2.1.3 Level 3: Move the Head Unit
    ----------------------------------

    The amplifiers are fine, but moving both the ground for the head unit
    and the signal cables does not solve the noise problem. Take the unit
    completely out of the dash, and put it on either the seat or carpet,
    and run new signal cables to the input of the amp. If this solves the
    problem, re-install the head unit, one step at a time and skip to level
    5. But if the noise persists, then move the head unit as close to the
    amp as possible and use the shortest possible signal cables. This will
    verify that the original signal cables are not causing the problem -
    assuming the noise is gone, reinstall the head unit one step at a time
    and go to level 5. Otherwise, there may be a problem with the power
    filtering for the head unit. As with the amps, power the head unit
    with an isolated power supply (again making sure that the head unit
    isn't touching the car's chassis at all). If the noise goes away, you
    can add power supply filtering or an isolated power supply; go to
    level 2. But if the isolated power supply does not solve the problem,
    then you can either replace the head unit and go to level 2, or check
    the car's electrical system in level 4.


    2.1.4 Level 4: Testing the Car
    -------------------------------

    There does not seem to be a problem with either the head unit or the
    amplifier, and the car's charging system is suspect. To see if this is
    the case, we can use a system in a car that is already known to be
    "quiet." Bring both cars together as if you were going to jump one,
    and use jumper cables to connect the two batteries. Start the engine
    of the car with the noise problem, and listen to the "quiet" car's
    system. If the noise does not go away, there is a SERIOUS problem with
    your car's electrical system (possibly a bad alternator). Have a
    qualified mechanic check the charging system out. If there is no noise
    in the "quiet" car, then the "noisy" car's charging system is
    definitely quiet, so continue with level 5.


    2.1.5 Level 5: Adding Signal Processors
    -----------------------------------------

    We have proven that the amplifiers are good, the head unit is good, and
    the car's electrical system is good. Now we need to reconnect each
    signal processor. Repeat this level for each signal processor used in
    your system; if you have added all of your signal processors, and
    there is no longer any noise, CONGRATULATIONS! You've removed the
    noise from your system! Connect the signal processor. If there
    isn't any noise, then go on to the next signal processor. Otherwise,
    try re-routing the signal cables. If this cures the problem, the route
    them permanently over the quiet path, and install the next processor.
    If not, then isolate the processor from the car's chassis except for a
    single grounding point. If this works, then permanently isolate the
    processor, and move on to the next processor. If isolation does not
    help, then advance to level 6.


    2.1.6 Level 6: Processor Isolation Tests
    ------------------------------------------

    Now, noise enters the system when one particular processor is
    installed, but regrounding it does not help. Move the processor very
    close to the amp, and check for noise again. If there isn't any, then
    re-install the processor, carefully routing the cables to ensure no
    noise, and continue at level 5 with the next processor. Otherwise, use
    an isolated power supply to power the processor, making sure that no
    part of the processor is touching the car's chassis. If this solves
    the problem, the consider permanently installing an isolated power
    supply or possibly a 1:1 transformer, and go to level 5 with the next
    processor. Otherwise, separate the processor and isolated power supply
    from the car by many feet and re- test. If there is still noise, then
    there is a serious problem with the processor's design. Get a
    different processor, and continue at level 5 with it. If separating
    the power supply and processor from the car does solve the noise
    problem, then either the processor is damaged, or your tests were
    inaccurate. Repeat level 5.


    2.2 My system "pops" when I turn it off. What is happening and how
    can I get rid of it? [JD]
    ================================================== ===================

    This kind of problem is often caused by transients in the signal
    processor as it powers down finding their way into the signal path,
    which the amplifier then transmits to the speakers.

    Usually this can be solved by adding a little turn-off delay to the
    processor. This allows the processor to stay powered on for a short
    time after the amplifiers have powered down, thus preventing the pop.

    Many components sold today (such as crossovers, equalizers, etc) have
    delays built-in. Read your manual to see if it is possible to set this
    delay on your piece of equipment or be sure to look for this feature
    during your next car audio purchase.

    If your processor does not have this feature, you can build your own
    delay circuit with a diode and a capacitor. Add a 1N4004 diode in
    series with the processor's turn-on lead, striped side towards the EQ.
    Then add a capacitor in parallel, the (+) side of the cap connects to
    the striped (processor) side of the diode, the (-) side of the cap goes
    to ground (not the radio or EQ chassis - connect to the car chassis).

    Experimenting with the cap value will give you the right amount of delay
    before the EQ shuts off. You don't want it too long, just long enough to
    make sure the amp is off before the EQ powers down. 220 - 1000 uF is
    about right, and make sure the cap is a polarized electrolytic, 16V or
    higher. Also keep in mind that the diode will introduce a 0.7V drop on
    the remote wire, which can cause the processor to power down before the
    rest of the system.


    2.3 What is the best power wire to use? [JSC]
    ================================================

    There is much debate over the benefit of certain wiring schemes
    (oxygen-free, multistranded, braided, twisted, air core, you name it).
    However, most people do agree that the most important factor in
    selecting power wire is to use the proper size. Wire is generally
    rated in size by American Wire Gauge, abbreviated AWG, or commonly just
    "gauge". To determine the correct wire size for your application, you
    should first determine the maximum current flow through the cable
    (looking at the amplifier's fuse is a relatively simple and conservative
    way to do this). Then determine the length of the cable that your will
    use, and consult the following chart, taken from the IASCA handbook
    (see Section 6.1),

    Length of run (in feet)
    Current 0-4 4-7 7-10 10-13 13-16 16-19 19-22 22-28

    0-20A 14 12 12 10 10 8 8 8
    20-35A 12 10 8 8 6 6 6 4
    35-50A 10 8 8 6 6 4 4 4
    50-65A 8 8 6 4 4 4 4 2
    65-85A 6 6 4 4 2 2 2 0
    85-105A 6 6 4 2 2 2 2 0
    105-125A 4 4 4 2 2 0 0 0
    125-150A 2 2 2 2 0 0 0 00

    If aluminum wire is used instead of copper wire, the next larger size
    (smaller number) should be used. You should also consider the
    installation demands: will you need to run the wire around corners or
    through doors or into the engine compartment? These sorts of problems
    in the car audio application require some special care in cable
    selection. You will want to have cable that is flexible; it should
    have thick insulation as well, and not melt at low temperatures. You
    don't want to install wire that is rigid and prone to cracks and cuts,
    or else the results could literally be explosive.
    Smell that? ......German leather and palm sweat.

  3. #3
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    2.4 What is the best speaker wire to use? [JSC, JW]
    ================================================== ====

    Again, there is much debate over the benefit of the various schemes
    that are being used by different manufacturers. In general, however,
    you will probably want to upgrade your speaker wire from the factory
    ~20 gauge to something bigger when you upgrade your amplifiers and
    speakers. In most cases, 16 or 18 gauge should be sufficient, with the
    possible exception of high-power subwoofers. According to an example by
    Jerry Williamson, using 18 gauge instead of 12 gauge would only result
    in a power loss of 0.1dB, which is essentially undetectable by humans.
    Thus, other factors play more important roles in the selection of
    speaker wire. One issue is that different wires will have different
    line capacitances, which could cause the wire to act as a low pass
    filter. Generally, however, the capacitances involved are so small that
    this is not a significant problem. Be sure to heed the warnings above
    regarding cable flexibility and insulation, especially when running
    wire into doors and other areas with an abundance of sharp metal.


    2.5 I heard that I should run my power wire directly to my car's
    battery. Why should I bother, and how do I do it? [JSC]
    ================================================== =================

    For some components, like head units and equalizers, it's acceptable to
    use the stock wiring for power. However, amplifiers generally require
    large amounts of power, and accordingly will draw large amounts of
    current. The factory wiring in most cars is not designed to handle
    large amounts of current, and most wires have 10-20A fuses on them.
    Thus, you will almost always want to run the power line for your
    amplifier directly to the positive terminal of the battery. This could
    require drilling a hole through the car's firewall, or at least
    spending time hunting for an existing hole (the steering column is a
    good place to start looking). Always remember to place a fuse on your
    wire as near to the battery as possible! For various reasons, such as
    an accident or simple wear and tear, your wire's insulation may
    eventually crack, which could allow the conducting wire to make contact
    with the chassis of the car and short the battery through this wire,
    which could lead to a serious fire. The closer you place a fuse to the
    battery, the more protected you are. Also, when running wire through
    areas with sharp metal corners, it is a good idea to use rubber
    grommets to provide extra protection against tearing through your
    wire's insulation.


    2.6 Should I do the same thing with my ground wire, then? [JSC, IDB]
    ================================================== =====================

    No. In almost every case, the best thing to do is to ground your
    amplifier to a point that is attached to the chassis of the car and is
    as close to the amplifier as possible. The ground wire should not need
    to be more than about eighteen inches long, and should be at least as
    large as the power wire. The point to which you make your ground
    connection should be an unpainted piece of bare metal.

    Some cars (Audi, Porsche) have galvanized bodies, and in these cars,
    you must find one of the manufacturers' grounding points or else some
    noise can result.


    2.7 Sometimes when I step out of my car, I get a really bad shock.
    What is wrong with my system? [IDB]
    ================================================== =====================

    Nothing. This is caused by static buildup by rubbing against the seats,
    floor mats, etc., just like walking across a carpet in a home. You can
    avoid this shock by touching something metal on your car _before_ you
    put your foot on the ground.


    2.8 When my car is running and I have the music turned up loud, my
    headlights dim with the music. Do I need a new battery or a new
    alternator? [CD, MO]
    ================================================== =====================

    The headlights will dim because of a momentary drop in the voltage
    level that is available to power the vehicle's accessories, including
    the headlights, amplifiers, the engine, etc. This voltage drop can be
    caused by a very large current demand by an accessory, such as an
    amplifier trying to reproduce a loud bass note.

    The first thing to do is to get your battery and alternator checked for
    proper functioning. A failing battery can place undesirable loads on
    the alternator, leaving less power for your system.

    If the power system appears to be working correctly, an improved
    alternator may be required for the large current demands of the audio
    system. When upgrading an alternator, be careful in your purchase, for
    there are some potential problems. An alternator which advertises a
    certain output level may only achieve that output at very high engine
    RPM ranges, for instance. Also, the new alternator must be adjusted to
    provide an output voltage within a reasonable range in terms of the
    voltage regulator.

    If you find your car will not start after playing the stereo for long
    periods of time with the engine off, and the present battery is in good
    working order, then another, paralleled battery could prevent this
    embarrassing problem.


    2.9 What is a "stiffening capacitor", and how does it work? [JSC]
    ================================================== =====================

    "Stiffening Capacitor" (note capitals) is a trademark of Autosound
    2000. However, "stiffening capacitor" (note lowercase), as a generic
    term, refers to a large capacitor (several thousand microfarads or
    greater) placed in parallel with an amplifier. The purpose of doing so
    is to provide a sort of reserve power source from which the amplifier
    can rapidly draw power when it needs it (such as during a deep bass
    note). The electrical theory is that when the amplifier attempts to
    draw a large amount of current, not only will the battery be relatively
    slow to respond, but the voltage at the amplifier will be a little lower
    than the voltage at the battery itself (this is called "line drop"). A
    capacitor at the amplifier which is charged to the battery voltage will
    try to stabilize the voltage level at the amplifier, dumping current
    into the amplifier. Another way to think about it is that a capacitor
    in parallel with a load acts as a low pass filter (see Section 3.10),
    and the voltage level dropping at the amplifier will appear as an AC
    waveform superimposed upon a DC "wave". The capacitor, then, will try
    to filter out this AC wave, leaving the pure DC which the amplifier
    requires.


    2.10 Should I install one in my car? If so, how big should it be,
    and where do I get one? [JSC]
    ================================================== =====================

    If you have a problem with dimming headlights when you have your music
    turned up and the bass starts to hit and the engine is running and you
    don't want to upgrade your alternator, or if the transient response of
    your amplifier is unacceptable to you, a stiffening capacitor could
    help you out. The commonly accepted "formula" for determining the
    proper size capacitor to use is 1F/kW (one farad per kilowatt). For
    example, a system running at 300W would need a 0.3F (or 300,000uF)
    capacitor.

    To install the capacitor, you should not simply attach it to your power
    and ground wires near your amplifier, as it will draw very large
    amounts of current from your battery and could blow fuses (or over
    charge). Instead, you should insert a small-value power resistor (25
    ohm, 1/2 watt) or a 12VDC test lamp in between the power lead and the
    capacitor, and then charge it. If you use a lamp in series with the
    cap, when the lamp goes out, the capacitor is done charging. When it
    is done charging, carefully remove the capacitor's leads from the
    charging circuit, being certain not to touch the two leads together.
    You may then permanently install the capacitor by wiring it in parallel
    with your amplifier (be careful not to short the leads!). Large caps
    are currently available from some audio dealers, such as Phoenix Gold.
    You could also try electronics shops or mail-order houses.


    2.11 What about adding a new battery? Or upgrading the amplifier?
    [IDB]
    ================================================== =====================

    Generally, adding a second battery is great if you want to listen to
    your stereo with the car turned off (and be able to start it again
    later!). As far as simply upgrading your current battery to a larger
    model, you may find that this will help solve the problem because
    batteries like the Optima 800 offer a larger number of cold cranking
    amps. However, the "response time" between when a battery kicks in a
    large amount of extra current and how long it takes a capacitor is
    vastly different.

    Although a battery may be able to respond in tenths of a second, bass
    notes are often much shorter and need current _immediately_ - which
    capacitors can supply. The difference between the two is that while
    the capacitor can supply a large amount of current immediately, their
    voltage quickly drops making them ineffective -- but by this time,
    usually the bass note has passed, and the capacitor has done its job of
    "stiffening" the supply voltage.

    Upgrading your alternator becomes a concern when you need a large amount
    of current from it frequently. If you are always listening to your
    stereo at a fairly high volume (assume your amp is drawing 20A), and
    then you use the A/C and a few other misc. accessories in your car, you
    can get to the point when the alternator can no longer provide enough
    current to effectively supply the car _and_ charge the main battery.
    So, the main battery is always supplementing the alternator's current
    supply, and slowly (but surely) dies a relatively quick death.
    Smell that? ......German leather and palm sweat.

  4. #4
    Join Date
    Aug 2003
    Location
    Tenn-uh-C
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    5,953
    My Cars
    ///Sedan Powered.
    3 Components
    *****************

    This section describes various components that you can have in a car
    audio system, along with common specifications, desirable features,
    some of the best and worst brands, and so on.

    Be aware that there is no standardized testing mechanism in place for
    rating car audio products. As such, manufacturers are open to
    exaggerating, "fudging", or just plain lying when it comes to rating
    their own products.


    3.1 What do all of those specifications on speakers mean? [JSC, CD]
    ================================================== ====================

    "Input sensitivity" is the SPL the driver will produce given one watt
    of power as measured from one meter away given some input frequency
    (usually 1kHz unless otherwise noted on the speaker). Typical
    sensitivities for car audio speakers are around 90dB/Wm. Some
    subwoofers and piezo horns claim over 100dB/Wm. However, some
    manufacturers do not use true 1W tests, especially on low impedance
    subwoofers. Rather, they use a constant voltage test which produces
    more impressive sensitivity ratings.

    "Frequency response" in a speaker refers to the range of frequencies
    which the speaker can reproduce within a certain power range, usually
    +/-3dB.

    "Impedance" is the impedance of the driver (see Section 1.1), typically
    4 ohms, although some subwoofers are 8 ohms, some stock Delco speakers
    are 10 ohms, and some stock Japanese imports are 6 ohms.

    "Nominal power handling" is the continuous power handling of the
    driver. This figure tells you how much power you can put into the
    driver for very long periods of time without having to worry about
    breaking the suspension, overheating the voice coil, or other nasty
    things.

    "Peak power handling" is the maximum power handling of the driver.
    This figure tells you how much power you can put into the driver for
    very brief periods of time without having to worry about destroying it.


    3.2 Are component/separates any better than fullrange or coaxials?
    [JSC, DK]
    ================================================== ====================

    Usually, yes. Using separates allows you to position the drivers
    independently and more carefully, which will give you greater control
    over your imaging. For best results, try to keep the mid and tweeter
    as close together as possible - this will make the two drivers act more
    like a single point source (which is ideal).

    For rear fill applications, however, coaxial speakers will perform
    fine, as imaging is not a primary concern. However, it is very common
    to use a low pass crossover with the rear speakers (at 2500 Hz) since
    rear-fill is intended to produce "ambiance," and high frequencies (>
    2500 Hz) can confuse the soundstage, making it appear that music is
    originating behind you.


    3.3 What are some good (and bad) brands of speakers? [JSC]
    ================================================== ===========

    People will emotionally defend their particular brand of speakers, so
    asking what the "best" is is not a good idea. Besides, the best
    speaker is the one which suits the application the best. In general,
    however, various people have claimed excellent experiences with such
    brands as Boston Acoustics, MB Quart, a/d/s/, and Polk. Also, most
    people agree that you should avoid brands like Sparkomatic and Kraco at
    all costs.


    3.4 What do all of those specifications on amplifiers mean? [JSC,
    BG]
    ================================================== ==================

    "Frequency response" refers to the range of frequencies which the
    amplifier can reproduce within a certain power range, usually +/-3dB.

    "Continuous power output" is the power output of the amplifier into one
    channel into a certain load (usually four ohms) below a certain
    distortion level (usually at most 1%THD) at a certain frequency
    (usually 1kHz). A complete power specification should include all of
    this information, e.g. "20W/ch into 4 ohms at < 0.03%THD at 1kHz"
    although this can also be stated as (and be assumed equivalent to)
    "20W/ch at < 0.03%THD". The amplifier should also be able to sustain
    this power level for long periods of time without difficulties such as
    overheating.

    "Peak power output" is the power output of the amplifier into one
    channel into a certain load (usually four ohms) below a certain
    distortion level (usually much higher than the continuous rating level)
    at a certain frequency (usually 1kHz). A complete power specification
    should include all of this information, e.g. "35W/ch into 4 ohms at <
    10.0%THD at 1kHz" although this can also be stated as (and be assumed
    equivalent to) "35Wch at < 10.0%THD". Consumer warning: some
    manufacturers will state the "peak power output" rating by including
    the amount of power which can be drawn from "headroom", which means
    power supply capacitors. They usually will not tell you this in the
    specification, however; indeed, they tend to prominently display the
    figure in big, bold letters on the front of the box, such as "MAXIMUM
    200W PER CHANNEL!!!" when the continuous rating is 15W/ch and the unit
    has a 5A fuse.

    "Damping factor" represents the ratio of the load being driven (that
    is, the speaker - usually four ohms) to the output impedance of the
    amplifier (that is, the output impedance of the transistors which drive
    the speakers). The lower the output impedance, the higher the damping
    factor. Higher damping factors indicate a greater ability to help
    control the motion of the cone of the speaker which is being driven.
    When this motion is tightly controlled, a greater transient response is
    evident in the system, which most people refer to as a "tight" or
    "crisp" sound. Damping factors above 100 are generally regarded as
    good.

    "Signal to Noise" or "S/N" is the ratio, usually expressed in decibels,
    of the amount of true amplified output of the amplifier to the amount
    of extraneous noise injected into the signal. S/N ratios above 90 to
    95dB are generally regarded as good.


    3.5 What does "bridging an amp" mean? [MHa]
    ==============================================

    "Bridging" refers to taking two channels of an amplifier and combining
    them to turn the amplifier into a one channel amplifier.


    3.5.1 Why should I bridge my amp?
    ----------------------------------

    For increased power. If your amp can handle the load, it will put out
    more power through a bridged channel than it would into through a
    non-bridged channel. Theoretically, a "perfect" amplifier that puts
    out X watts into Y impedance into each of two channels will put out 4X
    watts into Y impedance into one bridged channel. Be aware that some
    amps more closely approximate that perfect amp than others, and some
    manufacturers build current limiters into their amps to allow them to
    remain stable into difficult loads at the expense of power gains.


    3.5.2 Why shouldn't I bridge my amp?
    -------------------------------------

    There are several reasons: you might need those extra channels; your
    amp might not be stable into the load your speakers present if the amp
    is bridged; you might be a hyper-perfectionist that can't stand the
    thought of an small increase in distortion; or perhaps you just don't
    need more power. Car audio power is relatively cheap, and if you are
    not trying to make a mega-gonzo system, you may not need to double your
    power.


    3.5.3 What happens when an amp is bridged?
    -------------------------------------------

    Basically, one channel's signal is inverted, and then the two channels
    are combined to form one channel with twice the voltage of either of
    the original channels.

    Ohm's Law for Alternating Current states that I = V/Z where I is
    current, V is voltage, and Z is impedance. We also know that P = IV,
    where P is power. If we use Ohm's Law and substitute into the power
    equation, we get P = V(V/Z), which can be rewritten as P = (V^2)/Z.
    Therefore, power is the square of voltage divided by impedance.

    Now, why do we care about all that? Because it explains precisely what
    happens when an amp is bridged. I'll give a practical example and
    explain the theoretical basis of that example.

    Imagine you have a two-channel amp that puts out 50 watts into each
    channel when driven into a load of 4 ohms per channel. Since we know P
    and Z, we can plug these numbers back into our power equation and find
    V. 50 = V^2/4 -> V = sqrt(200). So, we're seeing a voltage of 14.1
    volts across each channel.

    Now, imagine we bridge this amp, and use it to push just one of those 4
    ohms loads. When the amp is bridged, the voltage is doubled. Since we
    know the voltage (2*14.1 volts), and the impedance (4 ohms), we can
    calculate power. Remember that P = V*V/Z. That means P = (28.2)^2/4,
    which is 198.1 watts. It should be clear by now that the new power is
    approximately 200 watts - quadruple the power of a single, unbridged
    channel!

    You can probably see that should be the case, especially if you look
    back at the power equation. Since P = V*V/Z, if you double V, you
    quadruple power, since V is squared in the power equation.

    Now, all this assumes the amp is stable into 4 ohms mono. The mono
    channel is putting out four times as much power as a single unbridged
    channel, so it must be putting out twice as much as the two single
    channels combined. Since the voltage on the supply side of the amp is
    dependent on the car's electrical system, it doesn't change (OK, the
    increased current might cause a voltage *drop*, but let's not worry
    about that now). Looking at the first power equation, at the supply
    side of the amp, we see P = IV. Now, when we bridged the amp, we
    doubled the power, but the input voltage stayed the same. So, if we
    hold V constant, the only way to double the power is to double the
    current.

    That means the amp is now drawing twice as much current when it's
    running at a given impedance mono than it would be running two stereo
    channels at the same impedance. There are only two ways the amp can do
    that - it can simply draw more through it's circuits, and dissipate the
    extra heat, or it can utilize a current limiter, to prevent the
    increase in current. Of course, using the current limiter means you
    don't get the power gains, either! So, if the amp can't handle the
    extra current, and it doesn't limit the current in some way, kiss it
    goodbye. For that reason, an amp is typically considered mono stable
    into twice the impedance it is considered stereo stable.


    3.5.4 Does bridging an amp would halve the impedance of the speakers?
    ----------------------------------------------------------------------

    Impedance is a characteristic of the speakers. The speakers don't give
    a flip how the amp is configured: they have a given impedance curve,
    and that's that. It should be clear that when you bridge an amp, you
    are changing *the amp*. The speaker's impedance is *not* a function of
    the amp, but the amp's tolerance to a given impedance depends
    completely on the way the amp is configured. If you'll remember from
    section 4, an amp bridged into a given impedance draws twice as much
    current as it would if it were driving two separate channels, each at
    that impedance. So, a four ohm speaker stays a four ohm speaker, if
    it's hooked to one channel, a bridged channel, a toaster, or the wall
    socket. But, it is more stressful for the amp to drive any impedance
    bridged than unbridged.

    So, why do people talk about the impedance halving? Well, it's a
    simple model that isn't correct but is easy to explain to people who
    don't know what's really going on. It goes like this: When you bridge
    the amp, each channel is "seeing" half the load presented to the amp.
    So, if you bridge an amp to 4 ohms, each channel "sees" 2 ohms.
    Therefore, each channel puts out twice as much power, and the combined
    output is quadruple a single channel at 4 ohms.

    Why is that still wrong? Because each channel isn't really used as a
    single channel. You've used part of one channel, and an inverted part
    of another channel to create a totally new channel, the bridged
    channel. Also, there's no way for a channel to "see" only part of a
    circuit. If it's "seeing" half the speaker, it's "seeing" it all.

    Second, it makes it awkward if people believe that the impedance is
    really, literally, changing. If you use that model, is it safe to run
    a 4 ohm mono stable amp into a 4 ohm speaker? It should be, but we
    just said the impedance halves, so that's now a 2 ohm speaker, and you
    can't use it. That's wrong, and confusing, and it makes people think
    they can't do things they really can.


    3.5.5 Can I bridge my 4 channel head unit?
    -------------------------------------------

    Generally, NO. Unless the manuals that came with your head unit
    specifically state that your head unit can be bridged, then do NOT
    attempt it - this could destroy the head unit's internal amplifier, and
    possibly void your warranty.


    3.6 What is "mixed-mono?" Can my amp do it? [JSC, IDB]
    ================================================== =======

    Some amplifiers which are both bridgeable and able to drive low
    impedance loads also allow you to use "mixed-mono" mode. This involves
    driving a pair of speakers in stereo mode as well as simultaneously
    driving a single speaker in bridged mono mode off of ONE pair of the
    amp's channels.

    To do this, you connect the mono speaker (typically a subwoofer) to the
    amp as you normally would in bridged mode, and then connect the left
    and right stereo speakers to the left and right stereo channels,
    respectively.

    However, for this to work, the amplifier must actually use both input
    channels in bridged mode. Many amplifiers, when placed in bridged
    mode, will simply "copy" and invert either the left or the right
    channel. This practice ensures high output to the mono speaker, but
    eliminates the possibility of mixed mono since you lose one channel.

    It is VERY important to use passive crossovers when configuring your
    amplifier in mixed-mono mode in order to keep from overloading the amp.
    The reason almost all new amplifiers are able to run in mixed-mono
    mode (even if they are only 2-ohm stable) is that the impedance seen by
    each channel of the amplifier is the same across the entire frequency
    spectrum when using passive crossovers. Here's how it works: Take a
    typical 2-channel amplifier that is stable to 2 ohms (stereo) or 4 ohms
    (mono). When the subwoofer is connected with a low-pass crossover (at
    100Hz, for example) then the amplifier "sees" a 2 ohm load on each of
    its channels (see 3.5) from 100Hz and down. When the full range
    speakers are connected with a high-pass crossover (at 125Hz, for
    example), the amplifier "sees" a 4 ohm load on each of its channels from
    125Hz and up. The passive crossovers prevent the amplifier from seeing
    more than one speaker on either channel at any given frequency. Of
    course, between the two crossover points the amp DOES see more than one
    speaker (and therefore the load on the amp dips to 1.33 ohms when using
    4 ohms speakers).

    A graph of impedance vs frequency for ONE channel of an amplifier would
    look similar to this when using 3 4-ohm speakers and crossover points
    at 100Hz(LP) and 200Hz (HP):

    +-----------------------------------------------------------+
    | ****************************************| 4
    | * |
    | * |
    |************* * | 2
    | * * |
    | * |
    | | 1
    | |
    | |
    +^-----^-----^-----^-----^-----^-----^-----^-----^-----^---^+ 0
    25 50 100 200 400 800 1.6K 3.15K 6.3K 12.5K 20K


    3.7 What does "two ohm stable" mean? What is a "high-current" amplifier?
    [JSC]
    ================================================== =========================

    An X-ohm stable amplifier is an amp which is able to continuously power
    loads of X ohms per channel without encountering difficulties such as
    overheating. Almost all car amplifiers are at least four ohm stable.
    Some are two ohm stable, which means that you could run a pair of four
    ohm speakers in parallel on each channel of the amplifier, and each
    channel of the amp would "see" two ohms. Some amps are referred to as
    "high-current", which is a buzzword which indicates that the amp is
    able to deliver very large (relatively) amounts of current, which
    usually means that it is stable at very low load impedances, such as
    1/4 or 1/2 of an ohm. Note that the minimum load rating (such as "two
    ohm stable") is a stereo (per channel) rating. In bridged mode, the
    total stability is the sum of the individual channels' stability *Note
    Bridging::.
    Smell that? ......German leather and palm sweat.

  5. #5
    Join Date
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    Tenn-uh-C
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    ///Sedan Powered.
    3.8 Should I buy a two or four (or more) channel amplifier? [JSC]
    ================================================== =========================

    If you only have one line-level set of outputs available, and wish to
    power two sets of speakers from a single amplifier, you may be able to
    save money by purchasing a two channel amplifier which is stable to two
    ohms rather than spending the extra money for a four channel amp. If
    you do this, however, you will be unable to fade between the two sets
    of speakers (without additional hardware), and the damping factor of the
    amplifier will effectively be cut in half. Also, the amp may run hot
    and require fans to prevent overheating. If you have the money, a four
    channel amp would be a better choice. You would need to add a dual-amp
    balancer in order to maintain fader capability, however, but it is more
    efficient than building a fader for a two channel amp. If you wish to
    power a subwoofer or additional speakers as well, you may want to
    purchase a five or six channel amp.


    3.9 What are some good (and bad) brands of amplifiers? [JSC, IDB]
    ================================================== =========================

    As with speakers, people emotionally defend their amplifier, so
    choosing the best is difficult. However, some brands stand out as
    being consistently good while others are consistently bad. Among the
    good are HiFonics, Phoenix Gold, a/d/s/, and Precision Power.

    Generally, "good" amplifiers tend to cost more (in money/watt) than
    "bad" amplifiers. So when you see an amp advertising 300W for only
    $100, and are comparing an amp with 50W for $300, you will usually find
    that the 50W/$300 amp will be of much higher quality than the 300W/$100
    amp.


    3.10 What is a crossover? Why would I need one? [JSC]
    ================================================== =====

    A crossover is a device which filters signals based on frequency. A
    "high pass" crossover is a filter which allows frequencies above a
    certain point to pass unfiltered; those below that same point still get
    through, but are attenuated according to the crossover slope. A "low
    pass" crossover is just the opposite: the lows pass through, but the
    highs are attenuated. A "band pass" crossover is a filter that allows a
    certain range of frequencies to pass through while attenuating those
    above and below that range.

    There are passive crossovers, which are collections of purely passive
    (non-powered) devices - mainly capacitors and inductors and sometimes
    resistors. There are also active crossovers which are powered
    electrical devices. Passive crossovers are typically placed between
    the amplifier and the speakers, while active crossovers are typically
    placed between the head unit and the amplifier. There are a few
    passive crossovers on the market which are intended for pre-amp use
    (between the head unit and the amplifier), but the cutoff frequencies
    (also known as the "crossover point", defined below) of these devices
    are not typically well-defined since they depend on the input impedance
    of the amplifier, which varies from amplifier to amplifier.

    There are many reasons for using crossovers. One is to filter out deep
    bass from relatively small drivers. Another is to split the signal in
    a multi-driver speaker so that the woofer gets the bass, the midrange
    gets the mids, and the tweeter gets the highs.

    Crossovers are categorized by their order and their crossover point.
    The "order" of the crossover indicates how steep the attenuation slope
    is. A first order crossover "rolls off" the signal at -6dB/octave
    (that is, quarter power per doubling or halving in frequency). A
    second order crossover has a slope of -12dB/octave; third order is
    -18dB/octave; etc. The "crossover point" is generally the frequency at
    which the -3dB point of the attenuation slope occurs. Thus, a first
    order high pass crossover at 200Hz is -3dB down at 200Hz, -9dB down at
    100Hz, -15dB down at 50Hz, etc.

    It should be noted that the slope (rolloff) of a crossover, as defined
    above, is only an approximation. This issue will be clarified in
    future revisions of this document.

    The expected impedance of a passive crossover is important as well. A
    crossover which is designed as -6dB/octave at 200Hz high pass with a 4
    ohm driver will not have the same crossover frequency with a driver
    which is not 4 ohms. With crossovers of order higher than one, using
    the wrong impedance driver will wreak havoc with the frequency
    response. Don't do it.


    3.11 Should I get an active or a passive crossover? [JSC, JR]
    ================================================== =============

    Active crossovers are more efficient than passive crossovers. A
    typical "insertion loss" (power loss due to use) of a passive crossover
    is around 0.5dB. Active crossovers have much lower insertion losses,
    if they have any loss at all, since the losses can effectively be
    negated by adjusting the amplifier gain. Also, with some active
    crossovers, you can continuously vary not only the crossover point, but
    also the slope. Thus, if you wanted to, with some active crossovers
    you could create a high pass filter at 112.3Hz at -18dB/octave, or
    other such things.

    However, active crossovers have their disadvantages as well. An active
    crossover may very well cost more than an equivalent number of passive
    crossovers. Also, since the active crossover has separate outputs for
    each frequency band that you desire, you will need to have separate
    amplifiers for each frequency range. Furthermore, since an active
    crossover is by definition a powered device, the use of one will raise
    a system's noise floor, while passive crossovers do not insert any
    additional noise into a system.

    Many people find it advantageous to use both active and passive
    crossovers. Often, a separate amp is dedicated to the subwoofers, to
    give them as much power as possible. The other amplifier is used to
    power the mids and tweeters. In this scheme, an active crossover is
    used to send only the sub-bass frequencies to the sub amp, and the
    other frequencies to the other amp. The passive crossovers are used to
    send the correct frequencies to the individual speakers (e.g., mids and
    tweeters).

    Thus, if you have extra money to spend on an active crossover and
    separate amplifiers, and are willing to deal with the slightly more
    complex installation and possible noise problems, an active crossover
    is probably the way to go. However, if you are on a budget and can
    find a passive crossover with the characteristics you desire, go with a
    passive.


    3.12 Should I buy an equalizer? [JSC]
    =======================================

    Equalizers are normally used to fine-tune a system, and should be
    treated as such. Equalizers should not be purchased to boost one band
    12dB and to cut another band 12dB and so on - excessive equalization is
    indicative of more serious system problems that should not simply be
    masked with an EQ. However, if you need to do some minor tweaking, an
    EQ can be a valuable tool. Additionally, some EQs have spectrum
    analyzers built in, which makes for some extra flash in a system.
    There are two main kinds of EQs available today: dash and trunk. Dash
    EQs are designed to be installed in the passenger compartment of a car,
    near the head unit. They typically have the adjustments for anywhere
    from five to eleven (sometimes more) bands on the front panel. Trunk
    EQs are designed to be adjusted once and then stashed away. These
    types of EQs usually have many bands (sometimes as many as thirty).
    Both types sometimes also have crossovers built in.


    3.13 What are some good (and bad) brands of equalizers? [HK]
    ================================================== ============

    Generally, companies that produce 1/3 octave (30 band) and 2/3 octave
    (15 band) equalizers are good. These include AudioControl, USD, Rane,
    Phoenix Gold. Most people try to stay away from equalizers that
    contain a "booster;" these are made by Kraco, Urban Audio Works and
    others.


    3.14 What do all of those specifications on tape deck head units mean?
    ================================================== ======================


    3.15 What are features to look for in a tape deck?
    ================================================== ==


    3.16 What are some good (and bad) brands of tape decks?
    ================================================== =======


    3.17 What are features to look for in a CD head unit?
    ================================================== =====


    3.18 Should I buy a detachable faceplate or pullout CD player? [IDB]
    ================================================== ====================

    It is getting difficult to find pullout CD players any more, since
    detachable faceplates are much more convenient to carry around.
    However, there is the obvious trade off - it is still possible to steal
    the chassis for the detachable face unit, when that is not possible
    with a pullout. Although some companies will advertise that it is very
    difficult to get replacement faces without the original receipt,
    thieves can still get the faceplates.

    Some companies, such as Eclipse, are starting to offer alternative
    methods for preventing theft. Some Eclipse decks now offer ESN
    (Eclipse Security Network), where the owner chooses a "key" CD that
    must be inserted to "revive" the deck should it lose power. The entire
    deck stays in the dash, with nothing to carry around; this expands on
    the trend towards convenience while offering the owner peace of mind.


    3.19 What are some good (and bad) brands of CD head units? [HK]
    ================================================== ===============

    Generally, Alpine, Clarion, Eclipse, McIntosh, Phillips and Pioneer are
    considered to produce good quality CD head units. They all have their
    problems, but these brands seem to be common and relatively
    problem-free.

    Bad brands include Kraco, Radio Shack, Rockwood and other "bargain"
    brands.


    3.20 Can I use my portable CD player in my car? Won't it skip a lot?
    [JSC]
    ================================================== ====================

    You can use any portable CD player in a car provided that you have
    either an amplifier with line level inputs (preferred) or a tape deck.
    If you have the former, you can simply buy a 1/8" headphone jack to RCA
    jack adapter and plug your CD player directly into your amplifier. If
    you have the latter, you can purchase a 1/8" headphone jack to cassette
    adapter and play CDs through your tape deck. The cassette adapters
    tend to be far more convenient; however, there is a significant
    tradeoff: by using cassette adapters, you limit your sound to the
    frequency response of the tape head, which is sometimes as much as an
    entire order of magnitude worse than the raw digital material encoded
    onto the CD itself.

    Portable CD players which were not designed for automotive use will
    tend to skip frequently when used in a car (relatively). CD players
    that are specially designed for automotive use, such as the Sony Car
    Discman, tend to include extra dampening to allow the laser to "float"
    across the bumps and jolts of a road. Some people have indicated
    success with using regular portable CD players in a car when they place
    the CD player on a cushion, such as a thick shirt or even on their
    thighs.


    3.21 What's that weird motor noise I get with my portable CD player?
    [JSC]
    ================================================== ====================

    Many people report problems while playing CDs from a portable CD player
    into their car audio systems. The problem, stated very simply, has to
    do with the stepping of the motor requiring a varying amount of current
    and non-isolated power and audio signal grounds. Using a liberal
    application of capacitors and inductors, this voltage variance can be
    restricted to a window of 8.990 to 9.005V for a 9V CD player, yet even
    the swing between these two levels is enough to cause annoyingly loud
    noise on the outputs. It has been reported that this entire problem
    can be solved by using a true DC-DC inverter at the power input to the
    CD player.


    3.22 What are some good (and bad) brands of portable CD players?
    ================================================== ================


    3.23 What's in store for car audio with respect to MD, DAT and DCC?
    [HK]
    ================================================== ===================

    MiniDisc (MD) seems to have a better future than Digital Audio Tape
    (DAT) or Digital Compact Cassette (DCC) which don't seem to have appeal
    to the public. Ease of use seems to be an important factor and the CD
    formats allows direct access to musical tracks at an instant. Although
    MD doesn't match the sound quality of the standard CDs it will probably
    be popular since the players have a buffer to eliminate skipping. DAT
    will remain as a media for ProAudio for recording purposes before
    pressing CDs.
    Smell that? ......German leather and palm sweat.

  6. #6
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    3.24 Are those FM modulator CD changers any good? What are my other
    options? [PW, JGr]
    ================================================== ===================

    Almost all manufacturers offer an FM modulator for their changers. As
    with all equipment, some are good and some are not. A person thinking
    about using an FM modulator must take into consideration that the sound
    quality will only be as good as the tuner in your head unit. Also, FM
    is limited in its frequency response. There is usually a noticeable
    loss of the high frequencies, due to the nature of transmitting via FM.

    If you do not want to use an FM Modulated CD changer, some
    manufacturers make controllers for changers that feature line-level
    (RCA) outputs. This allows you to connect the changer directly to an
    amplifier, bypassing the stock system altogether. Some models offer
    line-level inputs, allowing you to connect the stock system to the
    changer (so you can continue to use your radio/tape). Clarion, Sony,
    and Kenwood make such units.

    Your third option is to use the aftermarket changer that corresponds to
    the stock unit in your car. Not all cars have this option, but it is
    becoming easier. (see Section 3.25).


    3.25 What kind of changer will work with my factory head unit? [PO]
    ================================================== ===================

    Many factory head units these days have the ability to control a
    remotely mounted cd changer. Generally, the head will have a button
    labelled "CD" to switch sources to the external changer. In this mode
    either the radio preset buttons and/or the tuner up/down buttons will
    control which CD and/or track is playing. Check your car's manual to
    make sure your head can control a changer and how the buttons work.

    Once you know your head can control a changer, you wonder "What kind of
    changer will work with my factory head unit?" Of course, the one the
    dealer wants to sell you will work. However, the dealer makes lots of
    money selling you a changer, and there are often other after-market
    solutions, usually involving an adapter cable and a name-brand changer.
    The dealer will tell you that their solution is better and that's why it
    costs so much more (often more than twice as much as an aftermarket
    solution).

    The car manufacturers are constantly changing the interfaces between
    their heads and changers, in an effort to get you to buy their solution.
    However, the after-market is constantly reverse-engineering the
    interfaces and providing alternative solutions for the cost-conscious
    consumer.

    Two companies that make such adapters are Precision Interface
    Electronics (or PIE, <http://www.pie.net>) and Peripheral Interface
    Components (<http://www.stinger-aamp.com/peripheral/s-ind.htm>). Check
    their web sites to see if there's an adapter for your car's factory
    head. They also list which changer(s) will work with their adapters.

    For example, many of Honda's late-model heads were made for them by
    Alpine, so the OEM changer you'd pay your friendly Honda dealer ~$700
    for is essentially the same as Alpine's changers. The only difference
    is the interface wiring, where they swapped two pins, specifically so
    you'd have to get it from the dealer. (If you're interested in the
    details, see
    <http://integra.cyberglobe.net/caraud...grams/DIN.html>). The
    after-market adapters for this head simply swap the pins back, so you
    can use the regular Alpine changer, which can be bought for ~$300.

    Once you know which adapter/changer combo will work, you can get it from
    your local car audio dealer or favorite mail order place. The advantage
    of getting it from a local dealer is that they'll be able to install it
    for you. However, if you have the time and are at all mechanically
    inclined, you should readily be able to install it yourself.


    3.26 What are some good (and bad) brands of CD changers?
    ================================================== ========

    You will find that those companies who make high-quality in-dash CD
    players will also make good CD changers. (see Section 3.19), for
    a list.


    3.27 Why do I need a center channel in my car, and how do I do it?
    [HK, JSC]
    ================================================== ==================

    If a proper center image isn't achievable via a two channel
    configuration, installation of a center channel can help. Since the
    majority of recordings are done in two channel, a two channel system
    designed correctly should be able to reproduce a center image which was
    captured during recording. A center channel is not simply a summation
    of the left and right channels, like bridging an amplifier; rather, it
    is an extraction of common signals from the left and right channels.
    This usually means the lead vocals, and perhaps one or two instruments.
    These signals will then be localized to the center of the stage,
    instead of perhaps drifting between the left center and right center of
    the stage. A signal processor is usually required in order to properly
    create a center channel image. The image should then be sent to a
    driver in the physical center of the front of the car, at an
    amplification level somewhat lower than the rest of the speakers. The
    correct frequency range and power levels will depend on the particular
    installation, though a good starting point is perhaps a pass band of
    250-3000Hz at an amplification level of half the power of the main
    speakers (3dB down).


    3.28 Should I buy a sound field processor? [DK]
    =================================================

    Sound field processors (also known as DSPs) are fun toys to play with,
    and can have some use, but it is generally good to keep the KISS
    principle in mind: Keep It Simple, Stupid.

    The fewer signal processors (this includes equalizers, and active
    crossovers) that are in your system, the less chance there will be for
    noise to enter your system. You'll also save money, have a lower noise
    floor. Surround sound processors and bass regenerators are nothing
    more than bells and whistles and are totally superfluous in a properly
    designed system.


    3.29 What are some good (and bad) brands of signal processors? [IDB]
    ================================================== ====================

    If you do decide to buy a signal processor, try to stick with reputable
    brands like: AudioControl, Clark, Crystal-Line, Phoenix Gold, Rane or
    Clarion. Try to stay away from brands such as Petras, Urban Audio
    Works and Kraco.


    3.30 I keep hearing that speakers for Company X are made by Company
    Y. What's the deal? [IDB, DK]
    ================================================== ====================

    Many of the speakers you've ever purchased or ever will purchase have
    been assembled in plants "along side" speakers from other
    manufacturers, but that does NOT imply in any way, shape or form
    whatsoever that the two brands are even VAGUELY similar. This is often
    done in order to reduce costs because purchasing your own gaussing
    stations and mass producing your own drivers takes a LOT of money to
    implement.


    3.31 What is a Line Driver? Do I need one? [LC,IDB]
    ================================================== ====

    A line driver is a device that amplifies a signal, such as the low-level
    signal output from a head unit. Line drivers are made to amplify the
    line level signal to as much as 10 volts or higher. This, of course, is
    useless unless the receiving end can handle 10 volts as input. To solve
    this problem, there are line receivers which bring the line level
    voltage down from 10 volts or more to about 1 volt. Usually, the line
    driver and receiver are placed as close to the sending signal source and
    destination as possible, to minimize noise pick up.

    The automobile is an inherently noisy electrical environment. So RCA
    cables may pick up noise as it makes its way to the amplifier. Note
    that noise here refers to the induced noise, not ground loop noise such
    as engine whine. A simple way to fight against this noise is to make
    the signal level carried in the RCA cable very high, thus increasing the
    signal's resistance to induced noise and resulting in a higher signal to
    noise ratio at the destination of the RCA cable. Most head units
    produce a fairly low output voltage (< 1.5 V), although recently high
    end head units advertise 4 volt or higher output, and won't usually need
    a line driver.

    The line driver will increase dynamic range in certain cases where
    excessive noise is masking the lower level signals. However, a line
    driver will not increase the dynamic range when used in a system with
    little noise to begin with.

    There is some truth to the claim that a line driver will let you play
    your stereo louder since there are cases where the amplifier still
    doesn't play at its full potential even when its gain is turned all the
    way up and the volume on the head unit is maxed out. Adding a line
    driver here will allow you to turn down the gain on the amp while using
    a lower volume setting on the head unit.

    But before you jump in with both feet, remember that all electronics
    has their own inherent noise. Thus if you don't have a serious case of
    induced noise, a line driver will do little good since it might add
    enough noise to offset what little noise it "takes away."

    The line driver is a patch to the noise problem rather than a fix so it
    is still not the ultimate solution. My personal experience has shown
    to ME that a properly installed system with none-malfunctioning
    components will have little noise, even if you use low grade components
    such as those made by the less desirable manufactures. Also, a lot of
    crossovers and EQ units have rather high low-level output signals.
    Some times as high as 8 volts. So be sure to take this into
    consideration.


    3.32 Can I play MP3 files in my car? [IDB]
    ============================================

    Unfortunately, MP3 (MPEG Layer 3) audio files written to a CD-ROM can
    not be played by any of the current "mainstream" head units or CD
    changers.

    Many knowledgable individuals have spent hours installing PCs into their
    cars or building specialized hardware to play MP3 files in their car.
    Although many of these systems have been "hacked" together, there are
    now a number of commercially available systems that can be purchased and
    installed.

    One of the best sources for information about playing MP3 files in your
    car is located at:

    <http://www.mp3car.com>

    This site provides links to many of the commercial products as well as
    the "hobbyist" projects that you could follow to build your own system.


    4 Subwoofers
    *****************

    This section describes some elements necessary for understanding
    subwoofers - how they operate, how to build proper enclosures, how to
    pick the right driver for you, and how to have a computer do some of
    the work for you.


    4.1 What are "Thiele/Small parameters?" [CD, RDP]
    ================================================== ==

    These are a group of parameters outlined by A. N. Thiele, and later R.
    H. Small, which can completely describe the electrical and mechanical
    characteristics of a mid and low frequency driver operating in its
    pistonic region. These parameters are crucial for designing a quality
    subwoofer enclosure, be it for reference quality reproduction or for
    booming.

    `Fs'
    Driver free air resonance, in Hz. This is the point at which
    driver impedance is maximum.

    `Fc'
    System resonance (usually for sealed box systems), in Hz

    `Fb'
    Enclosure resonance (usually for reflex systems), in Hz

    `F3'
    -3 dB cutoff frequency, in Hz

    `Vas'
    "Equivalent volume of compliance", this is a volume of air whose
    compliance is the same as a driver's acoustical compliance Cms
    (q.v.), in cubic meters

    `D'
    Effective diameter of driver, in meters

    `Sd'
    Effective piston radiating area of driver in square meters

    `Xmax'
    Maximum peak linear excursion of driver, in meters

    `Vd'
    Maximum linear volume of displacement of the driver (product of Sd
    times Xmax), in cubic meters.

    `Re'
    Driver DC resistance (voice coil, mainly), in ohms

    `Rg'
    Amplifier source resistance (includes leads, crossover, etc.), in
    ohms

    `Qms'
    The driver's Q at resonance (Fs), due to mechanical losses;
    dimensionless

    `Qes'
    The driver's Q at resonance (Fs), due to electrical losses;
    dimensionless

    `Qts'
    The driver's Q at resonance (Fs), due to all losses; dimensionless

    `Qmc'
    The system's Q at resonance (Fc), due to mechanical losses;
    dimensionless

    `Qec'
    The system's Q at resonance (Fc), due to electrical losses;
    dimensionless

    `Qtc'
    The system's Q at resonance (Fc), due to all losses; dimensionless

    `Ql'
    The system's Q at Fb, due to leakage losses; dimensionless

    `Qa'
    The system's Q at Fb, due to absorption losses; dimensionless

    `Qp'
    The system's Q at Fb, due to port losses (turbulence, viscosity,
    etc.); dimensionless

    `n0'
    The reference efficiency of the system (eta sub 0) dimensionless,
    usually expressed as a percentage

    `Cms'
    The driver's mechanical compliance (reciprocal of stiffness), in
    m/N

    `Mms'
    The driver's effective mechanical mass (including air load), in kg

    `Rms'
    The driver's mechanical losses, in kg/s

    `Cas'
    Acoustical equivalent of Cms

    `Mas'
    Acoustical equivalent of Mms

    `Ras'
    Acoustical equivalent of Rms

    `Cmes'
    The electrical capacitive equivalent of Mms, in farads

    `Lces'
    The electrical inductive equivalent of Cms, in henries

    `Res'
    The electrical resistive equivalent of Rms, in ohms

    `B'
    Magnetic flux density in gap, in Tesla

    `l'
    Length of wire immersed in magnetic field, in meters

    `Bl'
    Electro-magnetic force factor, can be expressed in Tesla-meters or,
    preferably, in meters/Newton

    `Pa'
    Acoustical power

    `Pe'
    Electrical power

    `c'
    Propagation velocity of sound at STP, approx. 342 m/s

    `p'
    Density of air at STP 1.18 kg/m^3 (rho)


    4.2 How does speaker sensitivity affect real world SPL? Will a higher
    sensitivity give me a larger SPL? [MS]
    ================================================== ======================

    When it comes to mids and highs, efficiency (sensitivity) is a fairly
    good indicator of output differences at the same power level. When it
    comes to subwoofer performance, the driver's sensitivity is irrelevant
    unless you are also specifying a box volume.

    An efficient sub requires a larger box to achieve equivalent extension
    to a less efficient sub. In a small box, the less efficient sub will
    actually be LOUDER at low frequencies at the SAME POWER as the more
    efficient sub.

    Linear excursion is a very good indicator of ultimate output capability
    (given sufficient power to drive the speaker to that point.) To make
    sound you must move air; therefore, the more air you move, the more
    sound you make. When comparing two speakers of equal surface area, the
    one with greater excursion capability will play louder given sufficient
    power.
    Smell that? ......German leather and palm sweat.

  7. #7
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    4.3 What are the enclosure types available? [JLD, JG]
    ================================================== ======

    Only the order of the enclosure itself is shown here. The addition of
    a crossover network increases the order of the system by the order of
    the crossover. Example: If a First-Order, 6dB/Oct. crossover (single
    inductor in series with the speaker) is used with a Fourth Order
    enclosure, the total system is a fifth order. Note: Air volumes and
    ratios shown here may not be to scale. This is designed to provide
    order information only.

    First Order
    Infinite-Baffle or Free-Air

    |
    |
    /
    /
    ||
    ||
    \
    \
    |
    |


    Second Order Second Order
    Acoustic- or Air-Suspension Isobaric* Acoustic-Suspension
    or Sealed (Compound Loaded)
    _______________________ _______________________
    | | | _____|
    | / | / /
    | / | / /
    | || | || ||
    | || | || ||
    | \ | \ \
    | \ | \____\
    |_______________________| |_______________________|


    Fourth Order Fourth Order Fourth Order
    Bass-Reflex or Passive Radiator Isobaric*
    Vented or Ported Bass-Reflex Bass-Reflex
    _______________ _______________ _______________
    | | | | | ____ |
    | / | / | / /
    | / | / | / /
    | || | || | || ||
    | || | || | || ||
    | \ | \ | \ \
    | \ | \ | \____\
    | | | | | |
    | | | / | |
    | | | / | |
    | ____| | | | ____|
    | | | |
    | ____ | \ | ____
    | | | \ | |
    |_______________| |_______________| |_______________|


    Fourth Order Fourth Order
    Single-Reflex Bandpass Isobaric* Single-Reflex Bandpass
    _________________ ____ _______________________ ____
    | | | | | | | | | |
    | / | | | | / \ | | |
    | / | | / \ |
    | || | | || || |
    | || | | || || |
    | \ | | \ / |
    | \ | | \ / |
    |_________|_______________| |_______________|_______________|


    Fourth Order Fourth Order
    Three Chamber Three Chamber Isobaric*
    Single-Reflex Bandpass Single-Reflex Bandpass
    ____________ ____________ ______________ ______________
    | | | | | | | | | | | |
    | / | | \ | | / \ | | / \ |
    | / \ | | / \ / \ |
    | || || | | || || || || |
    | || || | | || || || || |
    | \ / | | \ / \ / |
    | \ / | | \ / \ / |
    |______|_____________|______| |_______|_______________|_______|


    Fifth Order = Fourth Order Enclosure + First Order Crossover
    = Third Order Enclosure + Second Order Crossover, etc.


    Sixth Order Sixth Order
    Dual-Reflex Bandpass Isobaric* Dual-Reflex Bandpass
    ____ _____________ ____ ____ ____________ ____
    | | | | | | | | | | | | | |
    | | | / | | | | | | / \ | | |
    | | | / | | | | / \ |
    | || | | || || |
    | || | | || || |
    | \ | | \ / |
    | \ | | \ / |
    |_______________|_____________| |______________|_____________|

    Sixth Order
    Three Chamber Quasi-Sixth Order
    Dual-Reflex Bandpass Series-Tuned Bandpass
    _ _________ _________ _ _________________ ____
    | | | | | | | | | | | | | | |
    | | | / | | \ | | | | / | | |
    | / \ | | / |
    | || || | | || |
    | || || | | || |
    | \ / | | \ |
    | \ / | | \ |
    |________|_____________|________| | ____| |
    | |
    | ____ |
    | | |
    |___________|_____________|


    Seventh Order = Sixth Order Enclosure + First Order Crossover, etc.

    Quasi-Eighth Order
    Series-Tuned Dual-Reflex Eighth Order
    Bandpass Triple-Reflex Bandpass
    _ _______________ _ ____________ _____________
    | | | | | | | | | | |
    | | | / | | | | | | |
    | / | | |
    | || | | |
    | || | | |
    | \ | |____ _____________ ____|
    | \ | | | | | | | |
    | ____| | | | | / | | |
    | | | / |
    | ____ | | || |
    |_____________|___________| | || |
    | \ |
    | \ |
    |______________|______________|


    * Isobaric or Coupled Pair (Iso-group) Variations:

    A variety of configurations may be used in the isobaric loading
    of any order enclosure. Physical and acoustic restrictions may
    make one loading configuration preferable to another in a
    particular enclosure.

    Composite or Push-Pull Compound or Piggy-Back
    or Face-to-Face Loading or Tunnel Loading
    _________________ ___________________________
    | | | ____|
    | / \ | / /
    | / \ | / /
    | >>> || || >>> | >>> || || >>>
    | >>> || || >>> | >>> || || >>>
    | \ / | \ \
    | \ / | \___\
    |_________________| |___________________________|

    Back-to-Back Loading Planar Loading
    _________________________ ___________________________
    | _________| | | |
    | \ / | / |
    | \ / | / |
    | >>> || || >>> | || >>> |
    | >>> || || >>> | || >>> |
    | / \ | \ |
    | /_______\ | \ |
    |_________________________| |________________________| |
    | |
    / |
    / |
    || <<< |
    || <<< |
    \ |
    >>> indicates direction of \ |
    >>> simultaneous cone movement. |__|


    4.4 Which enclosure type is right for me? [IDB, DK]
    ================================================== ====

    This answer is not designed to tell you exactly what kind of enclosure
    to build, but rather to give an idea of the advantages and
    disadvantages to the simple configurations (Infinite baffle [1st
    order], Sealed [2nd order], Ported [4th order] and basic bandpass).
    Building and designing more complicated systems (order > 4) is not for
    the light at heart.


    4.4.1 Infinite Baffle ("free-air")
    -----------------------------------

    * Advantages...
    - No box necessary!

    - This means it's usually cheaper to design and implement
    in your system

    * Disadvantages...
    - Requires that a good seal be obtained between front and
    rear of driver. In a car, this can be quite difficult and
    may require the installer to remove trim panels to plug any
    holes that would let energy "bleed through".

    - The responsibility for damping cone motion rests solely
    on the driver's suspension. As fatigue sets in, this becomes
    a critical issue in infinite baffle set-ups.

    - Less efficient in the sub-bass region than above
    mentioned enclosures.

    - Potentially more expensive drivers than good boxable
    woofer - The suspension must be extremely hearty and
    long-lasting to withstand high power applications.


    4.4.2 Sealed Box
    -----------------

    * Advantages...
    - Small enclosure volumes

    - Shallow (12 dB/Octave) roll off on low end

    - Excellent power handling at extremely low frequencies

    - Excellent transient response/ group delay
    characteristics

    - Easy to build and design

    - Forgiving of design and construction errors

    * Disadvantages...
    - Not particularly efficient

    - Marginal power handling in upper bass frequencies

    - Increased distortion in upper bass over ported design

    - When using high power and small box, magnet structure
    is not in an ideal cooling environment


    4.4.3 Ported Box
    -----------------

    * Advantages...
    - 3-4 dB more efficient overall than sealed design

    - Handles upper bass frequencies better with less
    distortion

    - Magnet is in good cooling environment

    - When properly designed, a ported box will slaughter a
    sealed in terms of low frequency extension

    * Disadvantages...
    - Size (not so critical outside the mobile environment)

    - Woofer unloads below Fb

    - More difficult to design/ can result in boomy, nasty
    sounding bass if misaligned


    4.4.4 Bandpass Box
    -------------------

    * Advantages...
    - When properly designed and implemented, can provide
    superior LF extension and efficiency.

    - Cone motion is controlled more and therefore mechanical
    power handling is increased.

    - Cones are physically protected from contents of trunk
    flying around.

    - Output is easily channeled directly into the interior
    of sedans.

    * Disadvantages...
    - Difficult to build (not recommended for newbies), and
    very sensitive to misalignment due to calculation or
    construction errors.

    - Their characteristic filtering often masks any
    distortion that occurs as a result of amplifier clipping or
    overexcursion and thus will give the user no warning that the
    driver is over-stressed and about to fail.

    - Need substantial mid-bass reinforcement to make up for
    narrow bandwidths in efficient alignments.

    - Transient response is largely dependent upon the
    alignment chosen....wider bandwidths will result in sloppier
    performance, narrower bandwidths (and thus higher effiencies)
    result in better transient performance.

    - They can oft times be quite large.


    4.5 How do I build an enclosure? [AO]
    ========================================

    These instructions are for building a first order (sealed) subwoofer
    enclosure. Building ported or bandpass boxes is more difficult, and
    those designs are less forgiving of mistakes. These instructions apply
    for all box designs, but be sure of the measurements before you make
    your cut. Building your own enclosure can save you a lot of money, but
    only if you don't need to buy all of your materials twice because of
    mistakes!

    You will need:

    *Wood*
    I only use MDF (see Section 4.6), but others have reported
    success using other hardwoods like birch and oak. Do not use
    plywood - it's far to flexible and porous. Use a minimum of 3/4"
    wood - flexing sub enclosures lose precious energy!

    *Screws*
    For one inch wood use #8 2 inch wood screws. For 3/4 inch wood use
    #8 1 3/4 inch screws. Double grip Drywall screws also work well.

    *Adhesive*
    I use "Liquid Nails" which comes in a caulk tube or a bucket, but
    any paste type of adhesive will work. Spray adhesives will not
    work.

    *Silicone sealant*
    White, brown, clear, caulk tube, or squeeze bottle, it doesn't
    matter. Make sure you don't get silicone lubricant (which comes
    in a spray can)!

    *Terminals/Terminal Cup*
    To allow easy connections from your amp.

    Besides these materials you will need several tools:

    *Table saw or radial arm saw*
    I use a radial arm saw, just because it's a little easier and
    accurate, but a table saw will work also. You can use a circular
    saw, but be very careful to make your cuts straight.

    *Jig saw*
    For cutting your speaker hole.

    *Drill*
    You will also need a 1/8" drill bit, a screwdriver bit, and a
    countersinking bit.

    *Pencil*
    To mark your cuts, make notes, etc.

    *Measuring tape*

    *Safety Goggles*

    *Face Mask*
    Breathing MDF dust has not been proven to cause health-related
    problems, but hang around with with a few installers at your local
    shop for an afternoon and you'll see why you need a face mask. :-)

    Start by marking the cuts you need to make on your wood. Double check
    your math, and your measurements.

    Use the table or radial arm saw to cut your wood. When you're done you
    should have six pieces of wood which fit together tightly to form a box.

    At this point you will need to trace the cut out for your subwoofer onto
    the front of the box. Remember that if you have a 10 inch subwoofer you
    do NOT want a 10 inch cutout. The 10 inch measurement is from the
    outside of the mounting ring. The actual cutout diameter should be with
    your instructions. Transfer the proper sized circle onto the sub box
    and cut it out with the jig saw. If you have trouble starting cuts with
    a jig saw, drill a 1/2" hole in the wood inside the circle. You can
    drop your blade into the hole and then cut out to the edge of the circle
    and around.

    After you have cut out your mounting hole you will need to cut out a
    square on one of the sides for your terminal cup. Transfer the proper
    size rectangle onto the wood and cut it out with the jig saw.

    Now you are ready to start assembling the enclosure. Choose one of the
    ends, and one of the sides. Apply a bead of adhesive along the edge of
    the end piece. Affix it to the edge of the bottom piece. Flip it over
    (have a friend hold the other end and hold the end in place,) and screw
    the edge to the end. Use one screw at each corner and then one more
    screw about every 8 inches. Drill a pilot hole with your 1/8" drill
    bit, then drill a countersink with your countersinking bit. Finally,
    drive the screw in. Make sure that you don't strip the hole.

    Repeat the above procedure with the other end. You should now have the
    two ends connected to one side. Affix the other three sides the same
    way.

    Finally, you'll want to seal the insides of the box with silicone. Apply
    a bead of silicone across all the inside edges and around the terminal
    strip.

    Allow the box to dry over night and then place your speaker into the
    hole. Screw it down and you're done!


    4.6 MDF for Dummies [IDB]
    ============================

    Since MDF (Medium Density Fiberboard) is used so frequently in building
    subwoofer enclosures and other projects, this section provides some more
    detailed information.


    4.6.1 What is MDF? [PS]
    ------------------------

    MDF (Medium Density Fiberboard) is a hardboard product comprised of hot
    compressed wood fibers glued together. The color of this material can
    vary from light to dark brown depending on the brand of manufacturer.
    Particle Board or Flakeboard consist mostly of recycled wood chips. The
    size of the wood chips used varies which means that the coarser the wood
    chips reduces the structural density of the material.


    4.6.2 Where can I get MDF? [PS]
    --------------------------------

    Wholesale distributors of lumber products. Home Improvement Centers,
    such as Home Depot or Home Base, and Lumber Yards may or may not stock
    MDF products, but they will be able to order it for you. Contact
    woodworking or cabinet making shops in your area, ask them where to get
    it or if it may be possible to buy the material from their business.


    4.6.3 What type of saw blade works best when cutting MDF? [PS]
    ---------------------------------------------------------------

    If you're using a circular saw, a good 40 tooth carbide tipped blade
    works best. If you're using a table saw, a 50/60 tooth carbide tipped
    combination or ripping blade will provide smooth cuts.


    4.6.4 What type of router bits work well with MDF? [PS]
    --------------------------------------------------------

    As far as router bits go, use only two flute carbide bits and make
    several passes as opposed to one single pass. If possible, trace the
    outline of what you intend to router and remove the majority of the
    material with a jigsaw which will reduce the amount of material being
    removed and will put less strain on the router as well, not to mention,
    this will all reduce the amount of MDF dust.


    4.7 What driver should I use?
    ================================


    4.8 Is there any computer software available to help me choose an
    enclosure and a driver? [JSC, MH, DK]
    ================================================== ==================

    Various enclosure design software is available via ftp from

    <ftp://ftp.uu.net/usenet/rec.audio.high-end/Software/>.

    The most popular program there is Perfect Box, which is in the file
    `perf.uu' (or `perf.zip').

    Note that NO program can tell you what enclosure is best for YOUR car!
    The program does not take into consideration your space limitations,
    the type of car you drive, the type and number of mid-bass drivers you
    use, your musical preferences and the goals you have for your system.
    Many people follow (blindly) what a computer program says is "optimal,"
    and end up unhappy with the results. Therefore, it is always a good
    idea to discuss a design you think looks good with a qualified
    installer or (even better) with the manufacturer.

    For an overview of many programs and devices available for enclosure
    design, obtain the file `sahfsd01.doc' at the ftp.uu.net archive. The
    filename stands for "Software and Hardware for Speaker Design", and was
    added to the archive in June 1994 by an anonymous contributor.
    Smell that? ......German leather and palm sweat.

  8. #8
    Join Date
    Aug 2003
    Location
    Tenn-uh-C
    Posts
    5,953
    My Cars
    ///Sedan Powered.
    4.9 What is an "aperiodic membrane?" [CD, DK]
    ================================================

    An "aperiodic membrane" is one part of a type of subwoofer enclosure.
    It is an air-permeable sheet which has frequency-dependent acoustical
    resistance properties. The original design goes back to Naim, for use
    in home systems, but has been applied by several individuals and
    companies in car audio.

    The completed system will be aperiodic, which means it will prove to be
    over-damped with a Q well below 0.7. In contrast, the most commonly
    used sealed enclosures have Qtc's in the range of 0.8 to 1.1 which are
    considered, by definition, to be underdamped. When improperly used, a
    high-Q system may have poor transient response, nasty peaks in
    frequency response, and high rates of roll-off. Aperiodic systems will
    feature excellent Aperiodic systems are characterized by better
    transient response, flatter frequency response and somewhat extended
    low frequency response.

    Another benefit of the system is that you can pretty much choose
    whichever driver you'd like to use, as long as they are big. The
    Thiele/Small parameters (which would normally determine what kind of
    box would be used) are taken into consideration by the membrane
    designers so that the response is extended and overdamped, regardless
    of the characteristics of the driver.

    Physically, the aperiodic membrane isn't for every car. It requires
    sealing the trunk from the passenger compartment in an air-tight
    manner, as well as sealing the trunk from the outside for best results.
    The drivers are then mounted into the baffle between the passenger
    compartment and the trunk, as would be standard in an
    infinite-baffle/free-air set-up. The aperiodic membrane is then placed
    either in front of the driver or behind the driver, depending on the
    type. When mounting behind the driver, the membrane is used as the
    rear-wall of a very small box which the driver sits in (as in Richard
    Clark's infamous Buick Grand National). So, in short, it's not
    suitable for trucks, jeeps, R/V's, or hatchbacks.

    You should probably only get an aperiodic membrane if you've got money
    to burn, lots of amplifier power, some big subs, a sedan, a desire for
    trunk space, and no wish to boom. If your tastes lean towards
    bass-heavy booming, as opposed to well-recorded acoustic instruments,
    you're not going to be pleased with the result.


    4.10 Can I use my subs in the winter? [MS]
    ============================================

    The following applies to all speakers in extremely cold conditions, but
    the question most often occurs in reference to subwoofers.

    The suspension of the speakers will stiffen considerably at very cold
    temperatures (lower than 30 degrees F). So will certain cone materials
    which may become more brittle.

    If a very cold speaker is played very hard there is a small potential
    for damage because more stress is placed on the cone's neck. The
    likelihood of damage is minimal for well-constructed and well-designed
    automotive speakers, however.

    Thermally, the danger is minimal because the ambient temperature and
    the coil temperature are so low that it is highly unlikely that a coil
    will overheat and burn, despite limited movement and ventilation.

    At temperatures between +20 degrees F and 0 degrees F, it is a good idea
    to play the system at a moderate level until the car's heater has warmed
    the vehicle interior. As the speakers warm up, they will play louder
    and lower signifying that their suspensions are warming up and returning
    to nominal compliance.

    If the temperature is extremely cold (less than 0 degrees F), you should
    avoid playing the system at all until the vehicle interior is warm.
    This is to avoid stress fractures in the surround material (especially
    with rubber surrounds).


    4.11 How can I carpet my enclosure? [AO]
    ==========================================

    What you will need:

    * Adhesive (3M Super 77 or Super 90 is excellent.)

    * Carpet.

    * A good sharp pair of scissors.

    * A razor sharp utility knife. Buy a BOX of blades, they go dull
    fast.

    * Solvent to clean up excess adhesive.

    Before you start, find a large, clean, flat surface on which to set the
    box as you carpet it. Start by unrolling the carpet onto the surface,
    smoothing it out so that its flat, and setting the box on top of it
    edgewise. Also, make sure that you remove the speaker, any ports and
    terminal cups from the box.

    The instructions on how to carpet the box are as follows:

    1. Place the box such that it is centered on the carpet lengthwise,
    and one edge of the box is about one inch from the edge of the
    carpet.

    2. Roll the box back so that the side of the box that was previously
    done faces forward, and the carpet beneath it is exposed. Coat
    both the box and carpet with adhesive, but do NOT apply the carpet
    to the box - the adhesive needs a few minutes to set up (follow
    the instructions from your adhesive to find out how long you
    should wait).

    3. After the adhesive has set up, roll the box back into position.
    Wait a few more minutes for the adhesive to bond.

    4. Now coat the side of the box adjacent to the remaining carpet (the
    side facing backwards) and the carpet next to it with adhesive,
    let the adhesive set up, and roll the side you just coated onto
    the coated carpet. Repeat this until three sides of the box are
    carpeted.

    5. Before carpeting the next side, the 1 inch of carpet sticking over
    the edge must be removed. To do this, rotate the box so that the
    first side that was carpeted is up. Pull the carpet sticking over
    the edge down towards the uncarpeted edge and cut it off with the
    knife, flush with the uncarpeted side of the box. You will have to
    run the knife nearly parallel to the uncarpeted side to get a
    perfect cut.

    6. This done, spray the remaining side and carpet, and roll the box
    onto it. Shear off the remaining carpet sticking out from all
    edges with the scissors leaving a 1 inch border everywhere.

    7. Clean up the ends of the box so that the carpet is flush with the
    sides of the box as in step 4.

    8. Next cut off the remaining 1 inch flap of carpet (located at the
    point where you began carpeting). This is the tricky part, as you
    don't want to be able to see this seam. Again, pull the flap down
    over the edge of the box, but this time cut it at roughly a 45
    degree angle. If you are successful you shouldn't be able to see
    the wood under the seam, but will probably see the white of the
    adhesive and the back of the carpet.

    9. Soak some of the solvent onto a rag and use this to scrub the edge
    you just cut off. It should dissolve the adhesive and the carpet
    backing somewhat, causing the carpet on the edge to become fuzzy.
    Keep scrubbing the edge until you can no longer see the seam.

    10. Now carpet the ends of the box. Cut two pieces of carpet slightly
    larger than the ends of the box and lay one of them flat on the
    surface. Spray the carpet and one end of the box with adhesive,
    and set the end of the box on the carpet, so the box stands on end.

    11. After the adhesive has dried sufficiently cut off the remaining
    border of the carpet as in 7 and 8.

    12. Repeat step 9 and 10 for the other end of the box.

    Congratulations! You've just carpeted your box!


    4.12 Are large magnets always better than small magnets? [ST]
    ================================================== =============

    Magnet *size* is meaningless!

    Every speaker will have an optimal BL ((see Section 4.1),) product,
    the field strength in the air gap multiplied by the length of the voice
    coil wire in the field.

    If the BL product is too low, the speaker is electrically not very well
    damped (which will result in a woofer with a high Qts). A bump in
    frequency response and a level drop in midband efficiency may be the
    result. If the BL product is too high, the speaker is electrically
    overdamped (Low Qts woofer). A very high midband efficiency, but the
    driver starts to roll of early.

    An high BL product can be achieved in a number of ways: increase field
    strength; or increase wire length in magnetic gap.

    The increase in field strength is limited; so some manufacturers use
    very thin wire for the voice coil, as such they can achieve a high BL
    product with a low field strength (cheap magnet). Or they use an 8 layer
    voice coil... needless to say that electrical power handling will
    decrease enormously.

    Long stroke woofers, having only a part of the voice coil in the air
    gap, need a very high field strength to achieve a high BL product. Often
    this means a big magnet as well...

    Use magnet size as an indication, but as nothing more than that.


    4.13 I know the box volume required for my subwoofer, but what are
    the best dimensions for my enclosure? [IDB]
    ================================================== ==================

    The specific dimensions of a subwoofer enclosure aren't really
    important. Once you know the appropriate volume of the box, and you
    know where in your car you want to install it, you will have some idea
    of the restrictions in the dimensions. For example, if the distance
    between the floor of your trunk and the bottom of the rear deck is 16",
    then you probably shouldn't make your box any taller than 16".
    Likewise, if width of the trunk (between the wheel wells is 38", then
    you've got that much space to work with.

    You can also infer some other information about your box, from the
    speaker specifications (for a PPI PC10):

    Mounting Depth: 4.5625"
    Speaker Displacement: .032 ft^3

    Here is an ASCII drawing of a subwoofer enclosure to help illustrate a
    few things:


    |--- L ---|
    __________ ___
    / /| |
    / + / | | + = Center of speaker
    / x / | D x = center of port
    /_________/ | |
    | | | _|_ W = Width of box
    | | / / L = Length of box
    | | / W D = Depth of box
    |_________|/ _/_

    Because of the speaker's mounting depth, you know that the box MUST be
    at 5.5" deep (it's always good to leave at least 1" of space behind the
    speaker, but leave more if you can). If you use a straight port (3"
    diameter PVC) then the box will need to be at least 13" deep (leaving 2
    inches between the end of the port and the back of other side of the
    enclosure), assuming that your port will reside completely within the
    enclosure. If you use Flex-Port or choose to have a portion of the
    port extending outside of the enclosure, you can make the box less deep.

    We also know that with a 10" woofer, the length and width should both
    be a minimum of 12" (leave 1" on either side of the woofer). Obviously
    both dimensions can't be 12" otherwise we can't put the port on the
    same face as the speaker.

    With volume, remember a couple of things. Recommended volume is the Net
    Internal volume. Both the speaker and the port will displace volume
    from the box - this means that you MUST account for these (i.e., make
    the interior volume of the box larger than the recommended value). In
    this case, you know the following:

    Required Volume: 1.25 ft^3
    Speaker Displacement: 0.032 ft^3
    Port Displacement: ??

    3" (interior diameter) PVC will usually have an exterior diameter of
    3.5" (0.25" wall thickness). Volume of a cylinder = pi*r^2*h, where r
    = 1.75" and h=12.25" (13" port length - 0.75" for the thickness of the
    MDF). Therefore the port displacement is: 117.9 in^3 or 0.068 ft^3
    (1728 in^3 = 1 ft^3).

    Required Volume: 1.25 ft^3
    Speaker Displacement: 0.032 ft^3
    Port Displacement: 0.068 ft^3

    TOTAL INTERIOR VOLUME: 1.35 ft^3 or 2332.8 in^3

    Now, to calculate the dimensions of the box: For a rectangular box, L
    x W x D = Volume.

    If we know that the minimum interior depth is 15" (because the port is
    13" and you should leave 2" between the port and the wall of the
    enclosure), we can say,

    L x W x 15" = 2332.8 in^3 or
    L x W = 155.52 in^2

    Since we know that L must be at least 12" (since the speaker is 10" in
    diameter), we can continue:

    12" x W = 155.52 in^2
    W = 12.96"

    So, we have determined that the interior dimensions of the box must be
    12" x 12.96" x 15". Obviously this can't work, since there is nowhere
    to put the port! You will either have to have the port extend outside
    of the enclosure, or use flex-port. Keep in mind that if you have part
    of the port "sticking out" of the enclosure, the Port Displacement will
    also change!!.

    For simplicity, (in this example) let's use flex-port. This will let
    you decrease the thickness of your box to about 6". So,

    L x W x 6" = 2332.8 in^3
    L x W = 388.8 in^2
    12" x W = 388.8 in^2
    W = 32.4"

    This is a little more reasonable. This will be a flat, wide box.
    Again, keep in mind that these are internal dimensions. If you use
    3/4" MDF (and you should) to build the enclosure, this will add 1.5" to
    each of these figures for the external dimensions. e.g.:

    13.5" x 33.9" x 7.5"

    Remember, the 6" depth and 12" length are just the minimum values, you
    can alter them if, for example, you don't have enough space between your
    wheel wells for a 34" box. If you only have, say, 28", then:

    maximum external width = 28"
    maximum internal width = 26.5"

    L x W x D = 2332.8 in^3
    L x 26.5" x 6" = 2332.8 in^3
    L = 14.7" (internal)

    Got it? It can be a pain, but that's part of the fun in building a
    speaker enclosure.

    5 Installation
    *******************

    This section describes how to do what you want once you know
    what it is you want to do.


    5.1 Where should I buy the components I want? [JSC]
    ================================================== ====

    Most of the time, you will either buy from a local dealer, or from a
    mail-order house. Buying from a local dealer can be good because you
    get to deal directly with a person: you can show them your car, ask
    specific questions, haggle prices, get quick service when there are
    problems, get deals on installation, etc. But there can also be
    advantages to buying mail-order: generally cheaper prices, sometimes
    better service, etc. In either case, you should always check prices
    before you buy, inquire about warranty service, and ask about trial
    periods.


    5.2 What mail-order companies are out there? [JSC, JM, MM, IDB]
    ================================================== ================

    *Crutchfield* - 800/955-3000
    1 Crutchfield Park, Charlottesville, VA 22906 USA

    * Advantages:
    - Great customer service

    - Generally knowledgeable sales and tech support personnel

    - Custom mounting kits, wiring harnesses, etc. free of
    charge.

    * Disadvantages:
    - limited product line

    - generally higher prices than local shops

    *J.C. Whitney* - 312/431-6102
    1917-19 Archer Avenue, P.O. Box 8410, Chicago, IL 60680 USA

    * Advantages:
    - Lots of "miscellaneous" items

    - 10kW amps for $19.99

    * Disadvantages:
    - 10kW amps that really only put out 1mW and break after first
    10 minutes of use.

    *Parts Express* - 800/338-0531
    340 E. First St., Dayton, OH 45402 USA

    * Advantages:
    - Large selection of electronics supplies at respectable prices.

    - Showroom prices said to be better than catalog prices.

    * Disadvantages:
    - Also carries some of the same quality-level components as
    J.C. Whitney.

    *Classic Research/Z-Box* - 520/571-0171
    5070 E. 22nd St., Tucson, AZ 85711 USA

    * Advantages:
    - Creates custom door panels with car audio in mind.

    * Disadvantages:
    - Only services expensive sports and luxury cars.

    *MCM Electronics* - 800/543-4330
    650 Congress Park Drive, Centerville, OH 45459-4072 USA

    * Advantages:
    - Sells lots of decently priced trinkets (fuses, fuse holders,
    wire, etc.)

    - Has excellent service and available technical support.

    * Disadvantages:
    - ?

    There are many other mail-order houses that can be found in the back of
    magazines, such as S.B.H. Enterprises, Speed and Sound and Smile
    Electronics, but people seem to have mixed feelings about these
    companies. The prices are very low, often due to the fact that these
    companies are not factory authorized - this means that there could be
    problems getting the unit serviced by the manufacturer should it break.
    To get around this, these mail order houses will often provide their
    own service departments, to repair defective units. Generally, it is
    advised to be careful when dealing with any mail order companies, to
    protect yourself.

    There are also a number advertisements for mail order houses (such as
    Apex Audio & Electronics or Insider's Audio) that offer special deals
    or free equipment if you buy their expensive catalog or pay a
    membership fee. While these ads may be enticing, keep in mind that
    they are often *too good to be true*! Usually you have to buy a large
    amount of equipment before you qualify for the "bonus" or the prices
    are very high for most equipment.


    5.3 What tools should I have in order to do a good installation?
    [JSC]
    ================================================== =================

    *Electrical tape*
    Make sure you get some that can withstand extreme temperature
    ranges.

    *Wire cutters/strippers and crimpers*
    Get a big pair with stripper holes precut for individual wire
    sizes.

    *Angled screwdrivers*
    Makes taking dash and rear deck speakers out a lot easier.

    *Multiple size screwdrivers, both flathead and Phillips.*
    Magnetic screwdrivers can be a big help when trying to get screws
    into (or out of) tight spaces.

    *Various wrenches, pliers, and socket sets*
    The specific sizes you need will depend on your vehicle.

    *Metal drill and saw*
    You'll need these if you need to modify your vehicle for new
    speaker cutouts or to accommodate a new head unit.

    *Hot glue gun*
    Good for putting carpeting or door panel trim back in place after
    modifications.

    *Razor knife*
    Helps for detailed modifications of door panels or carpeting,
    especially when installing new speakers.

    *Wire*
    (see Section 2.3).

    *Soldering Iron*
    Makes excellent connections, but can be messy if not careful.

    *Shrink wrap or flex tubing*
    Good for protecting wire, especially in the engine compartment.

    *Multimeter*
    Helps to diagnose installations.

    *Extra hardware*
    Screws, nuts, bolts, connectors, etc.

    *Fuse puller and extra fuses.*
    In addition to the fuses for your stereo system, check your car's
    fusebox to find the various sizes you'll need. Also, you can use
    needle-nosed pliers to pull fuses.

    *Wire ties*
    Helps to tuck wire away in otherwise exposed areas.

    *Small light source*
    A flashlight will do - you just want something that you can poke
    around the innards of your car with.

    *Tape measure*

    5.4 Where should I mount my speakers?
    ========================================


    5.5 What is "rear fill", and how do I effectively use it? [HK, JSC]
    ================================================== ====================

    "Rear fill" refers to the presence of depth and ambiance in music. A
    properly designed system using two channels will reproduce original
    rear fill on the source without rear high frequency drivers. Since
    recordings are made in two channels, that is all you will need to
    reproduce it. What is captured at the recording session (coincident
    pair mics, Blumlein mic patterns, etc.) by a two channel mic array will
    capture the so called rear fill or ambiance. Many of the winning IASCA
    vehicles have no rear high frequency drivers. Also a lot of this has
    to do with system tuning. If rear high frequency drivers are added,
    however, the power level of the rear fill speakers should be lower than
    that of the front speakers, or else you will lose your front-primary
    staging, which is not what you want (when was the last time you went to
    a concert and stood backwards?). The proper amount of amplification
    for rear fill speakers is the point where you can just barely detect
    their presence while sitting in the front seat. Separates are not a
    requirement for rear fill; in fact, you may be better of with a pair of
    coaxial speakers, as separates may throw off your staging.


    5.6 How do I set the gains on my amp? [JSC]
    ==============================================

    The best way to do this is with a test tone and an oscilloscope (*Note
    Oscilloscope::.) Since most people have neither item, the following
    will work approximately as well.

    1. Disconnect all signal inputs to the amp

    2. Turn all sensitivity adjustments as low as possible

    3. Turn head unit on to around 90% volume (not 100% or else
    you'll have head unit distortion in there - unless you've got
    a good head unit) with some music with which you're familiar,
    and with EQ controls set to normal listening positions

    4. Plug in one channel's input to the amp

    5. Slowly turn that channel's gain up until you just start to
    notice distortion on the output

    6. Turn it down just a wee little bit

    7. Disconnect current input

    8. Repeat steps 4-7 with each input on your amp

    9. Turn off head unit

    10. Plug in all amp inputs, and you're done

    If by some chance you do have an oscilloscope (and preferably a test
    disc), you do essentially the same thing as above, except that you stop
    turning the gains up when you see clipping on the outputs of the
    amplifier.

    Note that if you are paralleling multiple speakers on a single amp
    output, you need to set the gains with all of the speakers in place,
    since they will be affecting the power and distortion characteristics
    of the channel as a whole.
    Smell that? ......German leather and palm sweat.

  9. #9
    Join Date
    Aug 2003
    Location
    Tenn-uh-C
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    5,953
    My Cars
    ///Sedan Powered.
    5.7 How do I select proper crossover points and slopes? [DK]
    ================================================== =============

    Basically, this requires a degree of patience. The subwoofer should be
    started off at about 100Hz and adjusted until you are happy with the
    sound. Keep in mind that the higher the crossover point, the more
    power the driver on the high-pass will be able to handle but raising
    excessively may cause the low-pass driver to sound raspy or unnatural.
    The idea here is to first make rough selections to protect the drivers
    and then to fine tune crossover point selections to achieve optimum
    fidelity. It's all a matter of what sounds good to you after that, but
    remember that even *minute* changes in crossover frequency can make
    dramatic differences in the way your system sounds and images.

    As a rule, subs should be crossed over no higher than 120Hz, a 6 1/2
    mid should be able to handle about 90 Hz, a 5 1/4" should be okay with
    about 100Hz, a 4" - about 500Hz, and tweeters vary from about
    3500-5000Hz. These points all assume the use of a 12dB/octave
    crossover ... if you have a steeper roll-off a lower crossover point
    may be chosen. Remember, these are not hard and fast rules but rather
    a rule of thumb to help you get started (and so you don't blow up all
    your speakers when you are setting your gains!).


    5.8 How do I flatten my system's frequency response curve? [IDB,
    DK]
    ================================================== =================

    First, you'll need a good quality equalizer - either a 2/3 octave
    (15-band) or 1/3 ocatve (30 band) equalizer or a quasi- parametric
    equalizer such as PPI's PAR 224 that allows you to choose the center
    frequency and bandwidth (Q) of each knob on the EQ. This will allow
    adjustments to very specific frequency ranges. Next, you'll need to
    get a hold of an RTA (Real Time Analyzer), which is an expensive piece
    of equipment that good shops will usually have. The shops can then
    equalize the system by making a measurement with the RTA, and varying
    the levels on the equalizer in order to make the overall response curve
    flat.

    Unfortunately, most shops will not do this for free, since proper
    equalization can take anywhere from a half hour to many many hours.

    Another method involves buying an SPL meter (available from Radio Shack
    for between $32 and $60) and a test disc (Autosound 2000 makes one that
    runs about $25) that plays discreet frequency ranges - in 1/3 octave
    groups. Then, moving through the range of frequencies, SPL
    measurements can be taken at each range, and you can plot out a
    "response" curve. You'll be able to see what frequency ranges need to
    be boosted and which need to be cut. This process will be time
    consuming (more so than an RTA, which can analyze the entire frequency
    spectrum simultaneously), but should be much less expensive than having
    it professionally done.

    One last note: While a smooth curve will get the most points at an
    auto sound competition, you must NOT rely only on the RTA to tell you
    what sounds good. Use the RTA to get a good start, and then use your
    (better, use someone experienced in tuning systems) ears to do the
    fine-tuning.


    5.9 How do I wire speakers "in series" and "in parallel?" [IDB]
    ================================================== ================

    Wiring speakers in series involves connecting at least two speakers so
    that the first speaker's positive lead is connected to the amplifier's
    positive terminal, and the negative lead is connected to the positive
    lead of the second speaker. If there is a third speaker, its positive
    lead will be connected to the second speaker's negative lead ... and so
    on. The last speaker in the chain will have its negative lead
    connected to the amplifier's negative terminal.

    Speakers that are wired in parallel are all connected to the positive
    and negative terminals of the amplifier. So, when two speakers are
    wired in parallel, you'll connect each speaker's positive lead to the
    amplifier's positive terminal, and you'll connect each speaker's
    negative lead to the amplifier's negative terminal.

    Be careful when wiring multiple speakers in parallel or series so that
    you do not exceed your amplifier's rating. To calculate the effective
    impedance of a number of speakers, use the following formulas:

    Series Connections:
    Z(t) = Z(1) + Z(2) + Z(3) + ... + Z(n)

    That is, add up all of the impedances for each speaker to
    get the total impedance. For example, with 3 4-ohm speaker
    in series, the total impedance is 4 + 4 + 4 = 12 ohms.

    Parallel Connections:
    1/Z(t) = 1/Z(1) + 1/Z(2) + 1/Z(3) + ... + 1/Z(n)

    That is, add up the inverse of the impedance of each
    speaker and invert the sum to get the total impedance. For
    example, with 3 4-ohm speakers in parallel, the total
    impedance is 1 / ( 1/4 + 1/4 + 1/4) = 1 / (3/4) = 1.33 ohms.


    5.10 Are there any alternatives for Dynamat? It's too expensive! [MM,
    PK]
    ================================================== =====================

    In this question, "Dynamat" refers to all commercial products that are
    marketed expressly for reducing ambient noise in the car. Dynamat,
    Stinger RoadKill, _et al._ all have similar pricing, so this question
    is intended to give non-standard options.

    There is a material known as "Ice Guard," which is used by roofing
    contractors. It is similar to Dynamat, both in thickness and density.
    It is self-adhesive on one side, and seems to work very well.
    Unfortunately, it is sold only in large quantities (225 ft^2 rolls),
    and runs about $70 for this much. Perhaps a few people could get
    together for a roll, or it might be possible to get scraps from a
    roofing contractor.

    MCM Electronics (see Section 5.2), sells a product called
    "Sound Deadening Pads" (part #60-2010) which cost $0.90 for each 10" x
    10" square.


    5.11 How many devices can I attach to my remote turn-on lead? [IDB]
    ================================================== =====================

    The remote turn-on lead that most head units will not provide very much
    current (usually 250-300mA), so there is a limit to the number of
    components you can activate with it. Generally, it is safe to hook up
    two devices to the lead without having to worry about problems.
    However, if you'll be activating more components, then you should
    probably use a relay.


    5.12 How do I wire a relay in my system? [IDB]
    ================================================

    There are two types of relays that are commonly used in 12-volt
    automotive applications: Single-pole Double Throw (SPDT) relays, which
    have 5 pins, and Single Pole, Single Throw (SPST) relays, which have 4
    pins. Depending on the application, you can use either of these; for
    remote turn-on leads (see Section 5.11), an SPST relay is fine,
    SPDT relays are often used in alarm installations. Make sure that you
    get a 12-volt relay - this specifies the voltage required to make the
    relay "switch."

    The connections on the two types of relays look like this:

    SPST SPDT
    ===================== =====================
    (87) (87)
    +---------+ +---------+
    | --- | | --- |
    | | | |
    (86) | | | | (85) (86) | | --- | | (87a - center)
    | | | | (85 - right)
    | | | | | |
    +---------+ +---------+
    (30) (30)

    Pins 85 and 86 connect to the coil which causes the relay to switch.
    On both relays, pins 30 and 87 are normally disconnected. When the
    relay is activated (switched) pin 30 and 87 are then in contact. The
    difference with the SPDT relay is that in the "normal" state, pins 30
    and 87a are in contact.

    To hook up a relay (either kind) for a remote turn on, make the
    following connections:

    *Pin 30*
    +12 Volts (Battery +)

    *Pin 87*
    Amplifiers' remote turn-on terminal

    *Pin 86*
    Head unit remote turn-on lead

    *Pin 85*
    Ground

    *Pin 87a*
    No connection (SPDT only)


    5.13 How do I design my own passive crossovers? [JSC, JR]
    ================================================== =========

    A "first order high pass crossover" is simply a capacitor placed inline
    with the driver. A "first order low pass crossover" is an inductor
    inline with the driver. These roles can be reversed under certain
    circumstances: a capacitor in parallel with a driver will act as a low
    pass filter, while an inductor in parallel with a driver will act as a
    high pass filter. However, a parallel device should not be the first
    element in a set; for example, using only a capacitor in parallel to a
    driver will cause the amplifier to see a short circuit above the cutoff
    frequency. Thus, a series device should always be the first element in
    a crossover.

    When like combinations are used, the order increases: a capacitor in
    series followed by an inductor in parallel is a "second order high pass
    crossover". An inductor in series followed by a capacitor in parallel
    is a "second order low pass crossover".

    To calculate the correct values of capacitors and inductors to use, you
    need to know the nominal impedance Z of the circuit in ohms and the
    desired crossover point F in hertz. The needed capacitance in farads
    is then 1/(2 * pi * f * Z). The needed inductance in henries is Z/(2 *
    pi * f). For example, if the desired crossover point is 200Hz for a 4
    ohm driver, you need a 198.9 x 10^-6 F (or 199uF) capacitor for a high
    pass first order filter, or a 3.18 x 10^-3 H (or 3.18mH) inductor for a
    low pass first order filter.

    To build a second order passive crossover, calculate the same initial
    values for the capacitance and inductance, and then decide whether you
    want a Linkwitz-Riley, Butterworth, or Bessel filter. An L-R filter
    matches the attenuation slopes so that both -3dB points are at the same
    frequency, so that the system response is flat at the crossover
    frequency. A Butterworth filter matches the slopes so that there is a
    peak at the crossover frequency, and a Bessel filter is in between the
    two. For an L-R filter, halve the capacitance and double the
    inductance. For a Butterworth filter, multiply the capacitance by
    1/sqrt(2) and the inductance by sqrt(2). For a Bessel filter, multiply
    the capacitance by 1/sqrt(3) and the inductance by sqrt(3).

    You should realize, too, that crossovers induce a phase shift in the
    signal of 90 degrees per order. In a second order filter, then, this
    can be corrected by simply reversing the polarity of one of the
    drivers, since they would otherwise be 180 degrees out of phase with
    respect to each other. In any case with any crossover, though, you
    should always experiment with the polarity of the drivers to achieve
    the best total system response.

    One other thing to consider when designing passive crossovers is the
    fact that most passive crossovers are designed based on the speakers'
    nominal impedance. This value is NOT constant, as it varies with
    frequency. Therefore, the crossover will not work as it has been
    designed. To combat this problem, a Zobel circuit (also known as an
    "Impedance Stabilization Network") should be used. This consists of a
    capacitor and resistor in series with one another, in parallel with the
    speaker, e.g.,

    ________ __
    + o----| |----o-----o + | | /
    INPUT | Xover | R1 | |/
    | | C1 | |\
    - o----|________|----o-----o - |__| \

    To calculate these values, R1 = Re (in ohms) x 1.25, and C1 = (Lces in
    henries / Re^2) * 10^6. See 4.1 for definitions of Re and Lces. R1
    will be in ohms, and C1 will be in uF (micro- farads). As an example,
    an Orion XTR10 single voice coil woofer has Re = 3.67 ohms and Lces =
    0.78 mH. So, R1 = 3.67 * 1.25 = 4.6 ohms. C1 = ( 7.8E-4 / 3.67^2 ) *
    10^6 = 57.9 uF (be careful with units - 0.78 mH = 7.8E-4 H)

    As with the definition of crossover slopes, the above definition of the
    phase shift associated with a crossover is also an approximation. This
    will be addressed in future revisions of this document.


    5.14 How do I build my own passive crossovers? [JSC]
    ================================================== ====

    This section assumes that you have a basic understanding of how to
    solder, so the actual assembly of the crossover is not discussed.
    Rather, tips on choosing the proper types of capacitors and inductors
    are given here.

    To obtain low insertion losses, the inductors should have very low
    resistance, perhaps as low as 0.1 to 0.2 ohms.

    Also, be sure to select capacitors with proper voltage ratings. The
    maximum voltage in the circuit will be less than the square root of the
    product of the maximum power in the circuit and the nominal impedance
    of the driver. For example, a 4 ohm woofer being given 100W peak will
    see a maximum voltage of sqrt(100*4) = sqrt(400) = 20V. Make sure that
    the capacitors are bipolar, too, since speaker signals are AC signals.
    If you cannot find bipolar capacitors, you can use two polar capacitors
    in parallel and in opposite polarity (+ to - and - to +). However,
    there are some possible problems with this approach: the forward
    voltage rating will probably not be equal to the reverse voltage
    rating, and there could be a reverse capacitance as well. Both
    problems could adversely affect your circuit if you decide to use
    opposite polarity capacitors in parallel.


    5.15 Can I split the single pre-amp output from my head unit to drive
    two amplifiers with a Y-cable? [IDB]
    ================================================== =====================

    [This section was written by someone who wishes to remain anonymous,
    but I will field any questions on the subject -IDB]

    Yes. When two loads are connected in parallel (such as with a Y-cable)
    they get the same voltage as each other. They do NOT get the same
    voltage as if only one load was connected because the head-unit has an
    internal resistance (typically around 600 ohms). So, given that the
    amp has a typical input impedance of around 10k ohms then we get
    something like this:

    ----------------------------- ----------------------------
    HEAD UNIT ________ | | AMP |
    ______| |_________Vamp___________ |
    | | R(head)| | | | | _ |
    __|__ |________| | | __|___ |__| - _ |
    / \ | | | | | -___|__
    | Vi | | | |R(amp)| | _- |
    \_____/ | | |______| __| _- |
    |_______________________________|________| - |
    | | |
    ----------------------------- ----------------------------

    for the single amp situation. Please realize that the R(head) and
    R(amp) are internal to the head unit and amplifier and in fact are not
    deliberately added resistors but are characteristic of the real world
    circuits (non-ideal) in the head-unit and amplifier (and eq's, etc.).
    These numbers are typical, check your specific equipment for its
    particular specs. the worst case situation is a high source output
    impedance and low load input impedance.

    So, assuming a typical head unit and single amp the voltage seen at the
    amp (Vamp) is given by (Ohms law/Kirkov's law/1st year EE/high school
    electronics technology class/etc.):

    R(amp)
    Vamp1 = Vi * ------------------
    R(amp) + R(head)

    Vamp1 = Vi * 0.94

    Now, putting two amps in parallel from the original signal, R(amp) is
    effectively halved while R(head) is unchanged. Using the same voltage
    divider formula we get:

    10000/2
    Vamp2 = Vi * ---------------------
    10000/2 + 600

    Vamp2 = Vi * 0.89

    So, for an Alpine 4V preout, Vi in the diagram (the open circuit head
    unit line level output) is 4V. Thus Vamp1 = 3.76V and Vamp2 = 3.56V.
    With two amplifiers' inputs connected in parallel, the voltage is
    reduced from 3.76V to 3.56V or approximately 5%, not a big deal.

    If you had a more typical 1V preout you would get Vamp1 = 0.95V and
    Vamp2 = .89V, also not a noticeable drop.

    This is also why this is slightly more susceptible to noise than a
    direct one-to-one connection. If the noise level inserted due to
    cabling was 0.1V per cable then the noise level in the signal reaching
    each of the two amps would be a slightly higher percent of the signal
    level but not doubled. (this is also why the 4V head unit is favored
    over the 1V unit for noise immunity: 0.1V noise / 3.76V or 3% is much
    less than 0.1V noise / 0.95V or 10% even in a one to one connection).


    5.16 How do I turn a stereo signal into a mono signal [BW]
    ================================================== ==========

    Creating a mono signal is often necessary when you are powering a
    subwoofer by bridging the amplifier. Many people do not realize that
    bridging an amplifier does not always provide a mono signal - many
    amplifiers will simply use only one input channel, which means that the
    subwoofer won't be receiving the full signal.

    Some amplifiers have a switch that will allow you to combine the left
    and right channels into a mono signal. Some signal processors and head
    units provide a subwoofer-out channel that can be switched between
    stereo and mono.

    If you don't have this feature on any of your equipment, you will need
    to provide a mono signal to the amplifier. The common thought is to use
    a Y-adapter to "combine" the left and right channels. However, by
    using a Y-adapter, you are actually summing the line voltages and
    directly shorting the left and right channels at the head unit, which
    could cause problems.

    The correct way to create a mono signal is to cut off the ends of the
    RCA cables, combine the signal grounds (the outer shield), and then use
    a 1 kOhm (1/4 watt, 5% tolerance) resistor to each of the center
    conductors. Solder and insulate the resistors so that you don't short
    them prematurely, and then connect the two resistors together. Connect
    the summed signal ground to the shield of the new RCA plug, and the
    summed center conductor to the center pin of the RCA plug.


    5.17 How do I determine a speaker's polarity? [IDB]
    ================================================== ===

    If you have a speaker and the terminals are no longer marked, you can do
    a simple test to determine which terminal is positive (+) and which is
    negative (-). This test is useful for midrange/midbass/subwoofers, but
    not for tweeters.

    Use a 1.5V battery (AA, C, D) and connect the (+) terminal on the
    battery to one terminal of the speaker, and connect the (-) terminal to
    the other terminal of the speaker.

    If the cone moves OUT, then the battery is connected "properly," i.
    e., the (+) terminal of the battery is connected to the (+) terminal of
    the speaker, and the (-) terminal of the battery is connected to the
    (-) terminal of the speaker.

    If, however, the cone moves IN, the battery has been connected
    "backwards," i. e., the (+) terminal of the battery is connected to the
    (-) terminal of the speaker, and the (-) terminal of the battery is
    connected to the (+) terminal of the speaker.


    5.18 How can I use an oscilloscope to set the gains in my system?
    [AO]
    ================================================== =================

    This section assumes you are already familiar with your oscilloscope and
    will not go into setting it up. If you haven't already, spend a few
    minutes with your scope's manual.

    You'll need a test disc with a variety of test tones. I use the official
    IASCA test disc, but there are some of the "Bass Discs" that have test
    tones as well. You do NOT want to use sweeps, only pure tones. There is
    an AutoSound 2000 disc (#101?) which has a signal which is unclipped for
    20 seconds, clipped for 5, and then unclipped for the last 5 seconds. I
    have never used the AutoSound 2000 discs, but know them to have
    excellent recommendations (as well as all the test tones you could ever
    need). Viewing this track on your scope's display could be useful if
    you've never seen clipping on an oscilloscope display before.

    You start by finding the clipping level of your head unit. Many of the
    better head units will not clip the pre-amp outputs, even at full
    volume, but it's always better safe than sorry. Disconnect the RCA's
    from your head unit. Pop in your test disc and skip to the track with a
    1 KHz tone. If your CD player has a repeat function, set it to repeat
    just this track. That way you won't have to skip back at the end of the
    tone. Set your bass, treble, fader, and balance all to center. Turn the
    volume all the way up. Probe your right and left front (and rear if you
    have them) one at a time. Your scope should show a wave, either a sine
    wave or a clipped sine wave. If you have a standard pure sine wave then
    all is good, and you're ready to proceed. If you have a clipped wave
    then you need to turn down the volume, one click at a time until you
    see a perfect sine wave on your scope's display. Remember this point, as
    this is the highest you can EVER turn up your head unit. After you set
    the level for one of your outputs the rest should be the same, but check
    them all just to be sure. The results will be the same if you leave the
    RCA's plugged into the head unit and disconnect them at the other end
    (from your amp/EQ/processor/whatever) but unless you have a remote
    control you'll be running back and forth to change the volume.

    If your head unit has subwoofer pre-amp outputs you'll need to test them
    using a different tone. I usually test subwoofer outputs at a level
    midway between the crossover points. For example, if your subwoofer
    outputs are crossed over at 80Hz then you would want to use a 40Hz test
    tone. Other than that the procedure for testing subwoofer pre-outputs is
    the same as testing front or rear outputs.

    Once you've found the clipping level of your head unit it's time to
    proceed down the signal chain. If you are using an EQ, preamp, DSP, or
    other processor (NOT including crossovers) test them next. Leave your EQ
    set the way you usually use it. Hook up the processor and probe all the
    outputs of your processors in the same method as you did your head
    unit. You should probe each of the outputs using tones that match the
    bands of your EQ. For example, if you have a 9 band EQ with bands at
    50/100/200/400/800/1.5k/3k/6k/12kHz you would probe your EQ 9 times,
    once with a 50 Hz test tone, once with a 100 Hz test tone, and so on. If
    your EQ also includes a crossover you'll need to follow the crossover
    procedure. If any of these processors are clipping you will probably
    need to turn down your head unit's volume control or make any
    adjustments on that unit that you can. For example, if you are testing
    an EQ and you have any bands excessively boosted, try bringing down
    that band first. That may be causing your clipping.

    To test your crossover you need to probe each output using a test tone
    that is midway between the high and low pass. For example, a channel
    which is crossed over between 100 Hz and 20 KHz (like a front channel)
    would be tested at 9950 Hz. Since you'll be hard pressed to find a 9975
    Hz test tone on your CD use the 10Khz tone. For a rear channel crossed
    over with a lowpass of 3500 Hz you would use a 1750 Hz tone. As you
    again would have problems finding a 1750 Hz tone on a CD use a 2 KHz
    tone. For a subwoofer channel lowpassed at 70 Hz you would use a 35 Hz
    tone. This one you may find on your CD, if not use 30 Hz or 40 Hz.

    Assuming your crossover has level settings you will want to turn the
    level for whatever channel you're testing all the way up and probe the
    output. Assuming the output is clipping, back the level down slowly
    until you see a perfect wave on your scope.

    Now it's time to check your amp's outputs. Hook up your amps and play
    the same test tones you were using on the crossover. Disconnect the
    speakers and then turn the gains all the way up. Probe the first
    channel's output. Adjust the gain the same way you did your crossover.
    Back the gain down slowly until your wave isn't clipping anymore.

    Voila! You are done. You have just effectively eliminated clipping from
    your system. If you turn your bass or treble up, or boost up a channel
    on your EQ you may introduce some clipping. After major EQ work you may
    want to redo this procedure, starting at the EQ.
    Smell that? ......German leather and palm sweat.

  10. #10
    Join Date
    Aug 2003
    Location
    Tenn-uh-C
    Posts
    5,953
    My Cars
    ///Sedan Powered.
    5.19 Why are kickpanels such a popular location for mounting speakers?
    [ES]
    ================================================== ======================

    There is a lot more to mounting speakers in the kick panels than just
    equalizing the path length difference (PLD). Two of which are: on-axis
    response, and angling for pattern control. On-axis response refers to
    the fact that most speakers sound best when listened to on-axis, or as
    close to on-axis as possible. Second, after mounting your speakers in
    the kick panels you can then angle the speakers to take advantage of
    their off-axis response to use output level to overcome any PLD that is
    still present. The pattern control I am mentioning is one of the ways a
    horn loaded compression driver works very well, they not only use
    amplitude to overcome any PLD that is still present they minimize early
    reflections that can destroy imaging staging and spectral balance.

    PLD can be improved more than marginally when you consider the stock
    locations in a lot of vehicles, or the locations most installers choose.
    Measure the PLD between tweeters when mounted high in the dash or at the
    front corner at the top of the door and you will notice its probably on
    the order of 24". This mounting setup requires a lot of amplitude
    adjustment to correct the problems induced by this difference. The
    nearer tweeter is out phase from the opposite side and is arriving much
    sooner and with much greater amplitude due to the fact is not as far
    away. When all these factors are added together, it is very difficult
    for even the most flexible DSP unit to correct. On top of that, not
    many people or installers have access to the necessary tools to properly
    set up time delays using a DSP - TEF, MLSSA or other very expensive
    time domain measuring equipment are required to do the job properly.

    There will always be trade offs involved and deciding which trade offs
    to take can be very hard. A small dropout due to phase cancellation will
    probably not be noticed by most people but most people will quickly
    notice when a vehicle is not imaging properly, and if you can move the
    problem to higher frequency where we determine localization more from
    amplitude rather than phase differences, it will be much easier to deal
    with. Also, if you minimize the time/phase difference it will be much
    easier to correct with amplitude.

    Some people complain that kickpanel mounting gives a low sound stage.
    However, keep in mind that when any stereo system is imaging properly
    the point sources can no longer be localized. When our brains can no
    longer localize the point sources it will then hear things at eye level.


    5.20 How can I build custom kickpanels? [MB]
    ==============================================

    Building custom kickpanels for your car is a fairly advanced task, and
    requires knowledge (and experience) in working with fiberglass. Auto
    Sound & Security published an article in the August 1996 issue that
    covered the basics of working with fiberglass.

    This is kick panels in a nutshell. It takes about 2 days to do this
    right, although it is possible to do overnight (a LONG night) in one
    vehicle.

    Step 1: Cover base area with plastic & duct tape.

    Step 2: Lay fiberglass over the entire area. Don't worry about getting
    the pieces cut to the exact size and shape, you will trim them later.

    Step 3: Build the baffles for your speakers.

    Step 4: After the fiberglass has cured, set the baffles (with the
    speakers properly mounted into the panels and use a backstrap to secure
    the baffle to the panels. Now, spend some time listening to the car and
    aim the baffles until you get the best image and stage in the car.
    Note: Take your time aiming the speakers - once you fix the baffles,
    you won't be able to readjust the speakers. You may want to spend a few
    days listening to different positions to determine what sounds best.

    Step 5: Remove the speakers from the baffle and fill from behind with
    self-expanding insulation foam. This will allow you to mold the baffle
    into the rest of the car.

    Step 6: After the foam has hardened, sand it to the shape you want the
    panel to have.

    Step 7: Lay fiberglass over the foam to form the top panel of the kick
    panel.

    Step 8: After the fiberglass has hardened, sand the surface smooth.
    This may require the use of a little bondo to get things perfect.

    Step 9: Remove the foam by grinding it out from the inside of the
    kickpanel.

    Step 10: Cover the panels with carpet, vinyl, leather, fleckstone or
    other substance of your choice.

    Step 11: Install the kick panels in the car.

    Step 12: Install the speakers in the panels.

    Step 13: Make speaker baffles from Plexiglas, and grilles.

    Step 14: Enjoy.


    5.21 What's worse for a speaker, too much or too little power? [IDB]
    ================================================== ====================

    Problems occur (in everyday operation) when distortion is fed to a
    speaker. This occurs MUCH more often when you are dealing with an
    underpowered system - typically the owner will turn up the volume too
    much or set the amplifier gains too high to try and get more volume
    from the system. These introduce distortion to the signal - this will
    destroy *any* speaker. ((see Section 5.22).)

    When a speaker is overpowered, however, it is not nearly as common to
    have these kind of problems, so speakers aren't blown as much. Of
    course, it is certainly possible to destroy a speaker (thermally) by
    overpowering it, but you'll have a pretty hard time doing this on your
    own, especially with standard car audio amplifiers.


    5.22 Why is distortion harmful to my speakers? [RK]
    ================================================== ===

    Distortion is hard on speakers for two reasons.

    Reason 1: Distortion causes the power spectrum to shift upwards in
    frequency. A bass note, when distorted, will have lots of high
    frequency energy. This will cause mid-ranges and tweeters to fry, if
    the amplifier is operating full range. It doesn't harm woofers,
    necessarily.

    Reason 2: Distortion causes the average power to be much higher.
    Typically, a music signal that never clips has an average power level of
    1/4 the peak power level for even the most compressed speed metal or
    pop. More dynamic music will be 1/8 the peak level or less on average.
    When you clip the amp hard, the average output moves up to the
    full-rated output of the amp or more. The peak to average ratio can be
    less than 2 to 1, with the peaks being at double the rated power of the
    amp, and the average being at the rated power of the amp or higher.

    Thermally, the speaker can handle the average power being 1/4 the rated
    power of the amp (little to no clipping), but it will have a much harder
    time with the average power being the amp's rated power or more (massive
    clipping). As you might expect, this is pretty hard on the amp, too.

    For transients, most speakers can handle a ton of power. But for long
    term signals, the power handling is much less.


    5.23 What tools do I need to cut Plexiglas? [PS]
    ==================================================

    A good quality Carbide Tipped Triple Chip saw blade is preferred when
    cutting Plexiglas. This reduces the amount of chipout on the opposite
    side of the material and produces a smooth edge.

    A Router can be used to cut Plexiglas as well. The Router should be at
    least 1.5 HP or better and with changeable collets for a 0.5" Shank
    quality 2 flute Carbide bit. This reduces the vibration and chattering
    when cutting and will produce a more smooth edge.

    Since Plexiglas is an acrylic plastic (polymer), heat generated by the
    saw blade or router bit when cutting will melt the material and create a
    glazed imperfection viewed from the face if you do not maintain a steady
    rate of cut. It is best that when cutting you do a rough cut first,
    then do the finished size cut to reduce stress on the cutting blade and
    equipment.


    5.24 Are there any other special requirements for working with Plexiglas?
    [PS]
    ================================================== =========================

    Check the protective paper covering for any rips, tears or folding at
    the time of purchase. In most cases if visual inspection is not done
    at the place of purchase, it's very difficult to prove product defects
    or damage done by the seller.

    Inspect all surfaces that will come into contact to reduce tearing and
    scratching of the protective paper covering and the Plexiglas finish.
    Make sure that the protective paper covering remains in place until all
    machining and milling tasks are finished.

    6 Competition
    ******************

    This section describes the competition branch of the car audio world -
    what it is, and how to get involved.


    6.1 What is IASCA, and how do I get involved? [JSC, HK, IDB]
    ================================================== =============

    IASCA is the International Auto Sound Challenge Association, a
    sanctioning body for car audio competitions held throughout the world.
    Competitors earn points at each competition, and those that perform the
    best each year can advance to the finals. Prizes (trophies, ribbons,
    and sometimes cash) are usually given out to the top competitors in
    each class at every competition.

    IASCA memberships can be purchased at your local car audio retailer, if
    they are an IASCA member. You can call IASCA at 602/437-4678 to get a
    list of IASCA shops in your area.


    6.2 What is USAC, and how do I get involved? [HK]
    ================================================== ==

    USAC is another sanctioning body, similar to IASCA. However, USAC
    places greater emphasis on SPL measurements than IASCA.


    6.3 What are the competitions like? [HK, CD, IDB]
    ================================================== ==

    [HK writes:]

    They are much like loud car shows: a lot of cars parked with their
    hoods/doors/trunks open showing their audio systems. There are two
    types of judging styles: 1) drive through - where competitors drive
    their own vehicles to judging stations to be judged, and 2)
    walk-arounds - where the teams of judges will walk around the event
    site and judge vehicles that fit within their judging assignments.
    Typically SPL is done first with the mic stand in the driver's seat and
    the competitor in the passenger side adjusting only the volume.
    Hearing protection must be worn. After SPL measurements are completed,
    RTA measurements are performed by playing pink noise. When the volume
    level is within the specified "window" around 90db-110db, the RTA judge
    will signal you out, and at that point you must exit the vehicle for
    the actual scoring measurements. The next area for judging should be
    sound quality where two judges will sit in your car and judge the sound
    quality based on IASCA's reference CD/tape. The next area is
    installation judging where the competitor has 5 minutes to explain and
    show the installation of his/her vehicle. It is very useful to have a
    picture book/album of photos of the installation that may not be
    visible to prove that items not visible do exist. When that is
    completed, the competitor can park the vehicle and show spectators the
    vehicle. These procedures may differ from show to show, and at the
    regional/final levels they are very strict in what can and can't be
    done, e.g. a judge will make sure no adjustments are made after SPL
    until after sound quality judging is over, ear protection, etc.

    [CD writes:]

    Most involve a lot of waiting around. Thus, they are perfect for
    meeting other people interested in car audio, and seeing some
    installations which may give you some ideas. They're also perfect for
    listening to some cars that sound a lot better and a lot worse than
    your own. In IASCA competition, the cars are judged on:

    * Installation Quality (187 pts possible)

    - Wiring (40 pts)

    - Source Units (15 pts)

    - Amplifiers (25 pts)

    - Speakers (25 pts)

    - Other Devices (25 pts)

    - Overall Creativity (30 pts)

    - Attention to Show Details (20 pts)

    - Security and Convenience Features (7 pts)

    * Sound Quality (248 pts possible)
    - Tonal Accuracy and Spectral Balance (100 pts)

    - Soundstage and Ambiance (65 pts)

    - Imaging (50 pts)

    - Sound Linearity (30 pts)

    - Ergonomics (+/- 3 pts)

    - Noise Adjustment (up to -20 pts)

    * Frequency Response - RTA (40 pts maximum)

    * Sound Pressure Level - SPL (1 point per dB)


    6.4 Should I compete? [CD]
    =============================

    You should compete if:

    a. You have an okay sounding stereo

    b. You have an okay installation (i.e. no amps/changers sliding
    around in the trunk)

    c. You'd like some pros to comment on your system

    d. Your feelings won't get hurt if you don't get first place

    e. You've been to a contest and talked to competitors about it

    f. You've read the rule book

    g. You've listened to a test disc in your car, and understand
    what the sound quality judges are listening for

    You can compete even if you don't do all of the above, but the
    recommendations will help you understand and gain the most from
    competing.


    6.5 What class am I in? [HK, JSC]
    ====================================

    This section is mainly geared toward IASCA.

    [HK,JSC write:]

    There are three classes: novice, amateur, and pro. The novice class is
    intended to be an unintimidating level where beginners can start out;
    however, a competitor may only be in the novice class for one year, at
    which time he is automatically moved to the amateur class. Most
    competitors stay in the amateur class indefinitely, unless they become
    affiliated with a car audio shop or manufacturer, at which point they
    are moved into the pro class.

    [CD writes:]

    Are you or were you employed by a car audio manufacturer or dealer?

    _Yes:_
    You compete in pro

    _No:_
    Is this your first year of competing?

    _Yes:_
    You compete in novice for the first year

    _No:_
    You compete in amateur

    Note that modifying your amplifiers, buying your equipment below
    retail, or being sponsored by a manufacturer or dealer will get you
    kicked into pro.

    Also note that any home built active gear in the signal path (e.g.
    custom built equalizers, crossovers, or noise gates) will get you
    kicked out of novice.

    Once you know what group you are, you next need to know what power
    category you are in. Add up the 4-ohm non-bridged rating of all your
    amplifiers, including your head unit if your head unit is powering
    speakers (rather than exclusively feeding amplifiers). Then, find the
    category you fit into:

    Novice 1-150 151-300 301-600 601+
    Amateur 1-150 151-300 301-600 601+
    Pro 1-150 151-300 301-600 601+
    Expert 1-600 601+

    Thus, if you had a Rockford Punch 4040 (20Wx4) and a Punch 60ix
    (30Wx2), with a head unit that put out 6Wx2 (powering, perhaps, a
    center channel) you're in the 151-300 class. It does not matter if
    your amps are bridged down to .002 ohms; it's only the 4ohm rating that
    counts. If you no longer used your head unit to power speakers, you
    would be in the 1-150 class.

    Competition is usually most vicious in the 151-300 and 301-600
    categories at typical contests.


    6.6 Where can I find out when these Sound-Offs are? [IDB]
    ================================================== ===========

    The best way to get the most current list is to call either of the
    sanctioning bodies (IASCA or USAC). They can be reached at
    602/437-4678 or 601/939-7828, respectively. You can also visit the
    Official IASCA and USAC pages on the web at the following URLs:

    IASCA - <http://www.iasca.com>

    USAC - <http://www.soundoff.org>


    6.7 How do I get sponsored by a manufacturer? [CM]
    ================================================== ===

    Ah, the green grass on the other side of the competitor's fence;
    sponsorship. Sponsorship is not the easiest thing to obtain. And it
    might cause more problems than you anticipated. Obtaining sponsorship
    really depends on how much dedication you show for competing and finding
    the right manufacturer sponsorship deal at the right time.

    Keep in mind that car audio manufacturers consider sponsorship a form of
    advertising. Each manufacturer has a different policy concerning
    sponsorship. They are looking for a competitor that has shown they are
    committed to competing for a long time. They want someone that has
    shown that they know how to win, but also, how to handle defeat
    gracefully. They want someone that is well known in competition
    circles, someone that new competitors can come to and ask questions
    about the system and the manufacturer's products. They are basically
    looking for people that will put their product out there for people to
    see and help sell the equipment.

    As a competitor, you must show that you are committed by to going to as
    many shows as possible. You must open up your their vehicle and show
    off the system. Manufacturers want a show system, which often means
    turning your vehicle into a "trailer queen." That may require you to
    buy a trailer and tow the vehicle to the shows you compete in (this also
    means that you may need a new daily driver). And of course, if your
    bought equipment below retail or were given the equipment, then you will
    be forced to compete in the Pro or Expert class.

    There are different levels of sponsorship. It usually starts with
    manufacturer technical support. The manufacturer will give direct
    technical assistance to the competitor. At larger shows, they may
    reserve a space for you in their "tweek and tune" area.

    Next, the manufacturers may let you buy equipment from one of their
    dealers or the factory and a discounted price. This will definitely put
    you into the Pro or Expert class. Some manufacturers will let you mix
    and match equipment from different manufactures. Others want you to use
    their equipment only.

    Then the manufacturer might start giving you equipment and providing
    some or all of the installation costs.

    The holy grail of sponsorship is when the manufacturer provides the
    equipment, installation, and pays some or all of your competition
    expenses. It takes a lot of money to travel to shows. By the time
    someone reaches this level, they are frequently hired as an employee of
    the manufacturer. This is a good way of making the car audio business
    your career.


    7 Literature
    *****************

    This section describes various literature which you can read to brush
    up on your car audio skills, or to keep current, or to see other
    people's installations, or whatever else you'd like.


    7.1 What magazines are good for car audio enthusiasts? [JSC, MI,
    NML, JR]
    ================================================== =================

    Car Audio and Electronics $19.95/year
    P.O. Box 50267 (12 issues)
    Boulder, CO 80323-0267 800/243-6400
    <CarAudio@ix.netcom.com>

    Car Stereo Review $17.94/year
    P.O. Box 57316 (6 issues)
    Boulder, CO 80323-7316 303/447-9330

    Auto Sound and Security $28.95/year
    P.O. Box 70015 (12 issues)
    Anaheim, CA 92825-0015 714/572-2255

    Car Sound Buyer's Guide $17.95/year
    939 Port Washington Blvd. (Quarterly)
    Port Washington, NY 11050 516/944-5940
    <carsound@aol.com>

    Car Hi-Fi #23.60/year
    Freepost (8 issues)
    TK660 081 943 5943
    Leicester KE87 4AW

    Bilstereo Forlags AB Skr ??
    Box 230 84 (? Issues)
    104 35 Stockholm 08-34 29 70
    Sverige (Sweden)
    <bilstereo@public.se>


    7.2 Are there any newsletters I can read? [IDB]
    ==================================================

    Unfortunately, AutoSound 2000 Tech Briefs is no longer in publication,
    and as a result, there are no more newsletters currently in publication.


    7.3 What books can I read? [JSC, JW, TT]
    ===========================================

    _Loudspeaker Design Cookbook_
    by Vance Dickason
    Published by Audio Amateur Press
    ISBN 0-9624191-7-6
    $25-$30

    _Designing, Building and Testing Your Own Speaker System_
    by David Weems
    Published by McGraw Hill
    ISBN 0-8306-3374-X
    $16.95

    _Killer Car Stereo on a Budget_
    by Daniel L. Ferguson
    Published by Audio Amateur Press
    ISBN 0-9624191-0-9
    $19.95

    _The Car Stereo Cookbook_
    by Mark Rumreich
    Published by McGraw-Hill
    ISBN 0-07-058083-9
    $24.95


    7.4 Can I contact any manufacturers on-line? [IDB]
    ================================================== ===

    Yes, there are a number of manufacturers who have started to use the
    Internet and can offer advice for component selection, installation and
    advice. A list of these manufacturers is available on the WWW, at the
    URL:

    <http://www.mobileaudio.com/intdir/>
    Smell that? ......German leather and palm sweat.

  11. #11
    Join Date
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    ///Sedan Powered.
    :

    That's all folks. I did not do this writeup, but i had some contribution to it in a few area's. The people that were involved in this one are some of the worlds best. I think they did a great job answering questions. Hope it helps

    i did write this one though
    http://www.bimmerforums.com/forum/sh...hreadid=166776
    Last edited by one; 01-15-2004 at 11:30 PM.
    Smell that? ......German leather and palm sweat.

  12. #12
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    ///Sedan Powered.
    :
    Smell that? ......German leather and palm sweat.

  13. #13
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    Damn, Knowledge is Power!

  14. #14
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    99' Cosmos ///M3
    make this a sticky up here.

  15. #15
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    Bumping this so I can find it later.

    Veery nice.
    97 Alpinweiss M3/4 5spd

    Tho' much is taken, much abides; and tho'
    We are not now that strength which in old days
    Moved earth and heaven, that which we are, we are,
    One equal temper of heoric hearts,
    Made weak by time and fate, but strong in will
    To strive, to see, to find, and not to yield.
    - Tennyson, "Ulysses"

  16. #16
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    someone should make this sticky.

  17. #17
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    consider this stuck...
    Let me get this straight... You are swapping out parts designed by hundreds of engineers that get paid thousands of dollars for something you bought at Pep Boys because your buddy who doesn't have a job told you it was 'better'?!?

  18. #18
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    Is it possible to download and printout hte whole text file?

    EDIT: I found a direct DL link! http://www.zjstech.net/~library/234/Car%20Audio.doc

    Maybe you'll want to add it to the top of this page?
    Last edited by Whatup1049; 02-05-2004 at 07:39 PM.

  19. #19
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    dang.
    blahosidfnsd

  20. #20
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    Removal instructions for most bmw's audio


    http://carstereohelp.com/strbmw.htm

    Just incase noone has that link. Another good one.
    Smell that? ......German leather and palm sweat.

  21. #21
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    best thread....EVER
    1997 328ic
    1999 528i

  22. #22
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    for the most part very good information for the majority of people.But outdated.

    But being the SQ guy that I am--i am compelled to provide a further definition of a few terms.

    Soundstage-refers to the imaginary stage which the performance is percieved to originate. It can be rearward or forward, but ideally it should be foreward (how Often Do you watch a concert backwards?)
    Aspects of soundstage are stage width, height and depth.
    Stage width is very obviously how wide does the stage seem to be in relation to the physical boundries of the vehicle. Does the stage extend apillar to apillar, is it inside the pillars. does it extend beyond the physical boundries of the pillars?

    stage height refers to the percieved height at which the stage seems to appear. the height should be stable at all frequencies. Ideally it should at or near eye level for most people or at the horizon line when looking out the windshield. Many vehicle will have a rainbowed stage where it will be higher in the center at upper and higher freqs and pull downward at lower midrange on the sides.

    Stage Depth refers to the realism of the media being reproduced. It should have a 3D effect and have a definite sense of space and positioning. There shoudl be "air" amound each image.
    Stage depth really does not refer to how far foward or deep the stage seems to originate, this is soudnstage relative to listening position.

    Imaging is a term to to describe the ability of a system to individually place certain instruments, vocals and sounds in their correct placement and proportion on the soundstage. Vocals are not always centered on the soundstage, they can be left of or right of center or placed anywhere else on the stage. Often the lead vocal will be center on the soundstage.
    Typical band placement will be vocal more foward in center of teh soundstage, drums will be positioned behind the vocalis, Lead Guitar on the left side of the stage and bass on the left--all dependent on how it was recorded and mixed.
    a vehicle with a center mono speaker CANNOT image perfectly--it can produce a center image but will not be able to reproduce the correct placement of any other images on the soundstage. there is much much more to imaging then reproducing a center image.

    also, center channels aside from Dolby reproduction is more or less dead in car audio. afterall its called STEREO not Trereo. 2 speaker stereo reproduction with proper speaker placement can reproduce a very stable and focused center image without the need for any additional speakers.

    next,
    Infinite baffle and Aperiodic can be achieved in hatchbacks or just about any vehicle as long as the basics of enclosure design are achieved. In both instances the subs must vent to an area larger than the VAS of the driver and the front and rear waves must be completely isolated from each other. I have an Integra (featured in 7 magazines internationally and featured in Autosound Secuirty May 2002) which had Idmax in IB config. I have also been competing with my Eclipse which had 4 10s originally and then 2 12s in the spare tire well in finite baffle. I simply cut out an 8" hole in the bottom of the well. Then used a PVC drain cover, which was then covered in a gortex type material to fill in the hole and protect the subs from moitsure and road debris.
    gortex is a breathable material that is water proof and moisture resistant.

    also, many of the magazines are no longer in existance-AS&S is gone. Car Stereo Review is now called Mobile Electronics.

    also the IASCA and USAC Classes have changed dramatically--they are now broken into 1-600 and 601+ power classes. names for the classes have changed as well. USAC has a much larger power class break down as well.
    DIYMA Sound Quality Team. TEAM JL AUDIO/MSE
    2010 MECA SQL Extreme World Champion
    2010 Elite Summer Nationals Extreme and SQ2 champion
    2009 MECA SQL Extreme 2nd
    2006 IASCA Steel Valley Regional Champion
    2006 IASCA SQC2 SVR Champion
    2005 IASCA Wold Champion Pro Street 601+
    '03/'04 IASCA World Finals 2nd Pro Street 1-600
    '02 USAC Spring Break Nationals Champion
    2003 ISQC Team Japan Top 5 SQ

  23. #23
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    Also I noticed that the write-up said that .6 % THD may be noticeable. You can BARELY hear 3% on a test tone, let alone real music. 6% is usually most noticeable. When you typically hear distortion it is in the 12-20% range.

    -Nate
    1995 M3 - Gone
    2007 335i Sport - Euro Delivery - Gone
    2009 335i Sport - Gone
    1995 M3 - Gone
    1998 4Runner - Current

  24. #24
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    dats a big piece of knowledge dude..
    www.CarAmpsonline.com - your one stop shop!
    Visit us for cheap car stereo deals
    www.carampsonline.com

  25. #25
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    Is this a custom write up? Or taken from someplace else? You mind if I post it someplace else? Trying to reduce the amount of audio questions, or at least educate.

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