Here is the deal. I have a farily elaborate aftermarket stereo. The problem at hand if you didn't catch it from the title of this thread is that I have some nasty alternator whine coming through my mids and highs.

I am sure your first instinct is to tell me that I have my signal lines and power lines too close together, but I don't beleive that s the case. The basic setup of the system is as follows:

The headunit is an in-dash flip out dvd player, with the processing unit installed behind the interior panels in the trunk all the way in the passenger corner of the car with the signal lines between the monitor and the processor run down the passenger side of the car. The car has two batteries. The the second battery is behind the back seat of the car on the drivers side. The power line between the stock battery and the Optima is a 1/0 gauge wire run down the drivers side of the car. The amplifiers are centered in the trunk. The Optima Battery has it own ground about a foot from it's negative terminal. The amplifiers share a ground through a distribution block with maybe 3 feet of wire between the amps and the ground. Except for right at the amplifiers, the signal lines never even come close to the power lines so I am not sure what the source of this whine is.

Any ideas as to what to do?

 

I've got a theory...

In car stereo competitions, some competitors like to score extra points by having mulitple batteries, but then have the batteries be empty shells - this is usually because the multiple battery setups are a lot more likely to have noise issues, from ground loops. The ground for the car is 12v negative, and though we call it a "ground", it's actually the source of electrons for our electric equipment, as electrons carry a negative charge. Now, because your batteries are grounded to different points, and thus get their electrons from different parts of the car's body, you'll have variances in resistance between the two grounding points, which causes electrons to flow easily to one point, but have more difficulty in getting to a second point. It's this electron "strain", sometimes referred to as VSERP (valence *something electron repulsion *something*) that causes that whine you hear. It's more commonly called Alternator whine because when your car is running, it usually has two sources of electron flow, the battery and the alternator - usually with different points of grounding. Because of the additional battery, you now have 3 different points of electron flow while the car is running, and the resistance variance has more than tripled. you have the variance between the main battery and the second battery, the main battery and the alternator, the second battery and the alternator, and the sums of two batteries and the alternator, the main battery and the altornator vs. the second battery, etc.

IASCA judges, therefore, will always verify that any additional batteries in a competing car system are real, in the circuit, and provide between 12v and 14.4 volts to the audio equipment.

Is there an easy fix? Probably not. Do you have a true discreet switch between the batteries, where the secondary one will only join the circuit if the car is not running? That's one solution, if you're really just looking for added time to run your system with the car parked. Even the thickets guage of wire, if you were to connect all the -12V points of the batteries and alternator will provide an amount of resistance - it's a tough thing for fix.

Wow, my answer was pretty complicated... Sorry about that.

 

I do have an isolator between the two batteries. I am going to purchase a ground look isolator and install in o the siglan lines between the monitor unit and cpu and see what that does for me. If that doesn't work I will install the ground loop isolators also betwen the cpu and amps. If that still doesn't solve the problem I am considering running a common ground in the form of a single 1/0 gauge wire the full length of the car and using that ground for both batteries and amps....hmm...just thinking outloud now.....ground loop isolator first

 

Yeah, those signal-level Ground Loop Isolators work by inhibiting the flow of electrons along a signal path, but some purists say it also degrades the audio signal flowing through them, which it does. Another thing for you to test would be removing the shield from your signal cables, or shielding the line-level cable directly to the car chassis. By taking components out the chain, you can usually figure out what area to fix.. for example, if your head unit is off or disconnected, does the whine go away? If so, its between the head unit and the amps.. if it doesnt, the noise is somewhere after that point.

 

Adam

You got the right idea. Tie all the grounds together to assure yourself similar potential and bonding. Might want to look at it from a HIRF point of view.