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Thread: Engine/electrical noise through speakers - how to remove?

  1. #1
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    Engine/electrical noise through speakers - how to remove?

    So I've noticed it for years, but it's starting to drive me insane - the engine noise (rpm-dependent) when I have the music down really softly.
    How do I remove this electrical interference noise? Is there a sort of suppressor I can fit to the wiring/loom behind the headunit to alleviate this?

  2. #2
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    There is a huge capacitor on my '91 located on front left wheel well next to strut mount and the guys on here said it was for radio noise suppression. Its wired to the + battery post and ground.

    IMG_20171114_100214988.jpg
    IMG_20171114_100144556.jpg

  3. #3
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    leave it off...... no need for in an 8-series.....haha

    Oem radio or aftermarket with seperate amp in the back ?

    Oem works on high voltage outputs (to prevent interference). Aftermarket usually 1.0v outputs.... they pickup interference (all kinds off solutions for this..... best is to re-route the cables).

    Or use OEM headunit on high voltage to 3e party amp that accepts high voltage inputs (using the existing wiring).
    BMW 850 CSI march 1994 (EU spec), SOLD. https://www.classiccars-forsale.com/...94-bmw-850csi/
    BMW 850 CSI november 1994 (EU spec)

  4. #4
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    Aftermarket headunit with stock amp and wiring.

  5. #5
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    Quote Originally Posted by tangcla View Post
    Aftermarket headunit with stock amp and wiring.
    Most likely it is the way the aftermarket head unit was installed but some times it can be issues with the ignition wiring/engine grounding.
    1) With the aftermarket headunit make sure the head unit is grounded and wired as per the original BMW wiring diagram.
    2) The BMW OE amp in the 8 uses a differential high level input (bridged amp speaker level +/- inputs) from the headunit. If the headunit was installed as a line output (typically 1V) or single ended high level speaker output by grounding one of the inputs to the amp then it provide an opportunity for the grounded input or the twisted pair unshielded wiring between the headunit and the amp in the trunk to pick up ignition noise.

  6. #6
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    Is there any real benefit in using the stock amp? Should I just connect the inputs and the outputs at the boot, and run it direct off the headunit?

    - - - Updated - - -

    Quote Originally Posted by m6bigdog View Post
    Most likely it is the way the aftermarket head unit was installed but some times it can be issues with the ignition wiring/engine grounding.
    1) With the aftermarket headunit make sure the head unit is grounded and wired as per the original BMW wiring diagram.
    2) The BMW OE amp in the 8 uses a differential high level input (bridged amp speaker level +/- inputs) from the headunit. If the headunit was installed as a line output (typically 1V) or single ended high level speaker output by grounding one of the inputs to the amp then it provide an opportunity for the grounded input or the twisted pair unshielded wiring between the headunit and the amp in the trunk to pick up ignition noise.
    1) The new headunit is connected via a BMW to DIN ISO harness. No additional wiring was added (with the exception of the antenna-on bridged to +12V ACC as the headunit doesn't seem to drive the amp...)
    2) Because it's wired using the ISO harness, I'm sure the speaker outputs are driving the amps that way. is there anything I can do (preferably a simple fix!) that can correct this?

  7. #7
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    My noise issue was caused by the way my amps wiring was configured, I needed a larger gauge and all was well, Crutchfield helped me to diagnosis my issue,

    Here--->https://www.crutchfield.com/S-uaG97Z...ion_guide.html

  8. #8
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    Here is your answer:
    1. Turn radio off
    2. Drive faster
    3. Roll windows down

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  9. #9
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    Quote Originally Posted by tangcla View Post
    Is there any real benefit in using the stock amp? Should I just connect the inputs and the outputs at the boot, and run it direct off the headunit?

    - - - Updated - - -

    1) The new headunit is connected via a BMW to DIN ISO harness. No additional wiring was added (with the exception of the antenna-on bridged to +12V ACC as the headunit doesn't seem to drive the amp...)
    2) Because it's wired using the ISO harness, I'm sure the speaker outputs are driving the amps that way. is there anything I can do (preferably a simple fix!) that can correct this?
    Is the noise present in the AM radio, FM radio and CD player or just one?
    Also, using the fader & balance evaluate to determine if the noise is present in all 4-channels or just one?



    The simple fix! is the one that works, unfortunately, it's complicated by the effort of finding it! Somewhere during my 50 years in electronics engineering I learned that!!
    That is; sometimes the simple/effective fix takes a lot of effort...
    It is possible simply installing a noise suppression filter across the +12 and ground at the head-unit will solve the problem but if that doesn't work it gets much more complicated.

    I would suggest taking a look at the Crutchfield "Noise suppression guide" as there is some good troubleshooting advice.
    But first, if the headunit manufacture suggest a chassis grounding wire make sure it is installed as recommended.
    Also, If you have access to a stock head-unit you may want to test to see if the noise is present with it installed! Make sure the "antenna-on bridged to +12V ACC" wiring modification is removed.

    The speakers in the 8 cannot be directly driven by a 4 channel headunit and replacing the BMW OE 10-Channel amp is not as simple as it would seem and the problem may have nothing to do with the OE amp. If you suspect the OE amp I would just swap in another OE amp to see if that fixes the problem.
    The BMW amp has an equalizer and electronic crossover ahead of the 10 individual audio amp channels to distribute the 4-channel headunit (stereo front & rear) to the individual speakers.
    The equalization is custom-tailored to the interior of the 8 and the electronic crossover is designed to divide up the audio bandwidth based on the capabilities of the individual speakers!!
    The 6 front amp channels include a right & left - tweeter, mid-range and woofer.
    The 4 rear amp channels include a right & left - combination tweeter & mid-range channel and woofer.
    Yep it is complicated, it's an 8.

  10. #10
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    Does this capacitor make a difference? Have you tried disconnecting it?

    Quote Originally Posted by JDP530 View Post
    There is a huge capacitor on my '91 located on front left wheel well next to strut mount and the guys on here said it was for radio noise suppression. Its wired to the + battery post and ground.

    IMG_20171114_100214988.jpg
    IMG_20171114_100144556.jpg

  11. #11
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    Quote Originally Posted by BMSman View Post
    Does this capacitor make a difference? Have you tried disconnecting it?
    I don't think I have this.

  12. #12
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    Quote Originally Posted by BMSman View Post
    Does this capacitor make a difference? Have you tried disconnecting it?
    I have not tried the stereo without the capacitor disconnected, but I will try that and see if it makes any difference. The stereo is original and sounds really crappy so I hardly ever listen to it. My car has only been on the road since Feb after working on it several months.

  13. #13
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    Quote Originally Posted by tangcla View Post
    I don't think I have this.

    Engine noise in the audio is typically either due to a ground loop or induced.
    One more test:
    With the volume turned all the way down is the engine noise present?
    If the noise is present with the volume turned down the noise is a ground loop issue (ground wiring) between the headunit and the amp.
    If the noise is present only with the volume turned up (noise level changes with volume level), then the headunit is amplifying/picking up the engine noise.

    The 1994-end of production 840/850 have the same audio system components and wiring harness.
    My 1997 850 doesn't have the noise filter cap.
    I upgraded my system to the CD43 headunit and E36 Top-HIFI amp and sound switch.
    Absolutely no engine noise with the stock headunit and amp or with the upgraded components!!

  14. #14
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    If aftermarket headunits are used, some headunits are more susceptible to electrical noises than others. I've been down this road many times before. On my very first revamping of the stereo system, I had zero interference noise. Due to being so picky with audio quality, I have had a number of iterations of stereo install...all high-end components used. Some of those installs were plagued with slight electrical noises. As m6bigdog has explained on a couple posts above, he's dead on with the culprits. Make sure your ground connections are clean, your RCA or high level speaker cables are separated as far aside from the power cables as possible. Your antenna connections can also pick up noises as well. A lot of factors that play into the entire scheme of radio installation on the 8.

  15. #15
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    Quote Originally Posted by m6bigdog View Post
    Engine noise in the audio is typically either due to a ground loop or induced.
    One more test:
    With the volume turned all the way down is the engine noise present?
    If the noise is present with the volume turned down the noise is a ground loop issue (ground wiring) between the headunit and the amp.
    ah, I forgot to mention this. When volume is turned all the way down, I can hear the noise. Sounds like my car is supercharged!

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