ECU interference on door speaker

Ameer Antar antar at
Wed Dec 13 13:57:21 EST 2006

I removed all the RCA cables from the amps and tried revving the engine, but the sound is still there, mostly on the right front door speaker. I know it's crazy, but I'm still suspecting that speaker wire near the ECU. It only comes over the tweeter which is probably more sensitive to interference. I will try taking out that wire tonight and update you guys.
-------------------- Original Message --------------------
From:Huw Powell [audi at]
To:Ameer Antar [antar at]
Cc:Quattro List [quattro at], Scott Phillips [Scottp at]
Date:12/12/06 8:39:34 PM
Subject:Re: ECU interference on door speaker

>>> Thanks for the info. Unfortunately, I already have everything
>>> setup that way. I have a ground cable directly from the batt to
>>> the a splitter and then onto the amps.
> Could you explain what problems doing that might have caused?

It shouldn't, really. What you are trying to avoid are "ground loops",
where you can find a "circuit" of ground wires. If one portion of this
circuit has any resistance, there will be a current induced in it by any
local RFI etc.

Picture this simple loop: chssis ground to head unit to
grounded/shielded interconnect to amp to another chassis ground. Noise
can be induced in the interconnect, and will get amplified. Hence the
desirability of "directional" interconnects - or separately accessed
shield grounds around two "live" signal conductors (like the XLR plug on
a typical recording mike cable).

> The only component that has a different ground is the head unit.
> Would running a ground from the battery to head unit possibly help?

Even better would be lifting it at the head unit and grounding it only
to the battery, same place as the amp. As someone else noted, watch out
for antenna grounds, as well.

>> It is being picked up in the head unit to amp run, obviously after
>> the volume control. You mentioned a "splitter" as well, I suppose
>> that is between the head unit and two amplifiers?
> Yes, there are splitters for each line, but even after connecting the
> amp directly to main patch cable, it's still noisy. So, I guess I
> could test this by disconnecting all patch cables to the amps. That
> should clarify if it's a power or audiocable issue, right?

Yes, I think so.

>> You might also have a compromised line level cable - one that is
>> not shielded properly, etc.
> I'm using those twisted pair patch cables. Are these any good?

I have no idea what those are. Are they shielded?

> How about those line-level noise filters? Do they affect sound
> quality much?

One kind I am familiar with uses a transformer coupling to break the
ground loop. I have one in my complex building stereo wiring, too many
runs of 50' of interconnect, devices grounded all over the place. I had
to lift a few grounds and break this loop in order to set things up the
way I wanted.

Sound quality is a religious issue so I will make no claims here, you'll
have to read between the lines.

BTW, the ground loop isolator I used was sold to solve a problem like
yours. But see if you can fix it without one, first.

Huw Powell



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