running dedicated ground wire, worth it?

So I've had an alternator whine coming through my speakers for quite some time. It changes with RPM, and gets louder with the headlights on. Car is a '96 Mazda Miata (so therefore has the battery in the trunk). I have two Eclipse amps in the trunk. One running the door speakers, one doing the tweeters.

It's beginning to get cold, and once the hardtop goes on, this whine will become that much more noticable and annoying. The RCAs going from the HU to the amps in the trunk do at one point pass into the trunk on the same side as the main positive cable going from the alternator to the battery. However, the noise doesn't seem to get any better or worse moving the RCA cable a little closer or further from the positive cable, and frankly, I'm just not buying that that is causing the problem.

I've tried two different ground loop isolators on the RCA cables with no luck. I've heard that sometimes it's necessary to run a dedicated ground wire from the HU to remote mounted amps to avoid engine noise through the speakers. Is there any electrical basis for this idea? Is it worth it? I just need to get rid of this whine somehow.

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'96 Mazda Miata

I have always tried that as one of my last tests. MOST of the time it has done nothing. Refresh my memory...what kind of radio are you using?

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Pioneer head unit perhaps?  If so, replace it.  Sometimes alternator whine is a symptom of problems in the vehicle's ignition system.  Have you replaced your spark plugs, wires and distributor cap lately?  How about  upgrading the big 3?

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Simple things how long is your ground? Is it grounded to bare metal no paint is your ground and powe wire the same size?

Head unit is an Alpine CDA-9811. I doubt anything is blown inside it that would be causing it. The only thing I should mention is I once did have an L-Pad in the system, and it did something odd once. I had installed a new Eclipse XA2000 amp, and for some reason it acted oddly when I turned the L-Pad for the tweeters all the way down, not like the old Eclipse 3122 I did have in there. It made sort of an odd pop/squeak out of the tweeters that also ended up damaging the L-pad itself. I really can't explain it any better than that, which is why I haven't mentioned it. It almost seems like things started making noise around then, but it's really hard to say.

However, it's very important to note that since then, the system has been totally changed around aside from the HU. Different speakers, different crossover, and the old 3122 amp is back to powering the tweets (which are what makes the noise, my crossover pretty much filters it out of the woofers). There's no way any kind of short caused by messing with the L-pad downstream from the amp could go through and take out something in the HU, which is of course on the other side of the amp from the L-pad, is there?

As far as the other questions... Like I said, it's a Miata, so the amps in the trunk are wired directly to the battery terminals both positive and negative. Positive and negative power wires are the same wire and about the same length. Both the plugs and wires are factory parts with less than 10K miles on each. Car has electronic ignition.

Upgrading the big three would be a little daunting in this car as upgrading the alternator positive to battery positive means running a heavy gauge wire the whole length of the car. I guess I could try the other two without much issue. I guess it would help if I knew exactly what causes the alternator whine to get picked up by the amps. I'm a little confused exactly what induces it into the whole system.

I think one thing I'll eventually have to try is to isolate the HU entirely from the chassis and run a ground wire straight back to the battery, effectively taking the chassis out of the system entirely as an electrical conductor.

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'96 Mazda Miata

How is the resistance between your headunit's ground lead SPECIFICALLY, and the RCA shield on the cables heading back to the amplifier? Test that with a multimeter, with the RCA's disconnected from the headunit, and check the DC resistance between the headunit's chassis or RCA shield, and the shield on the RCA's coming from the amplifier. After you check the DCR, turn the car on, and check for voltage, both AC and DC at/between the same points.

Anything over about .1 ohms, or ANY AC voltage, or about 1VDC, could indicate a poor bond between the battery and somewhere on the body. Most accessories are grounded to the body, and in all (as far as I know) a uni-body design is used, and with one common battery bonding point, there's probably a bad or dirty connection.

AC voltage might indicate a diode going bad in your alternator.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Ok, so let me clarify, you're saying check the resistance and voltage between...

1) Ground wire going into HU and outer barrels of RCA cables plugged into HU... With RCAs uplugged at HU.

2) Head unit chassis or RCA shield (what is the head unit's RCA shield?) and outer barrel of RCA connectors at amp... Is this with them plugged in or unplugged at the amp and HU?

I guess you just said too much right there for me to pick apart exactly what to put each lead of the meter on, and what should and shouldn't be plugged in. Again the problem is I don't know how sound works its way into the system, so I don't understand what I'm looking for, otherwise the tests would make logical sense to me.



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'96 Mazda Miata