Got engine noise?
Alot of people, most actually, that enjoy car audio have tried chasing down engine noise, and heard all the "tricks" to fixxing this. (Grounding together, or all at battery, or use triple shielded RCAs etc etc)...all are false or half true at best. Below is a reply from audio guru, and king of 12 v knowledge Richard Clark describing why noise happens, and how to keep it from happening, or minimizing its effect in the car. Its a long read, but faster than ripping a set of RCAs out.
"Let me give an abbreviated explanation of how a signal conductor usually picks up alternator wine------if you are familiar with a transformer you know a few basic things-----current flows through the primary winding and creates a magnetic field in the core-----this magnetic field in turn causes a current in the secondary winding since it also is looped around the magnetic core------the way alternator whine is injected into a signal conductor of a car is exactly the same way-------in a car we don't have a primary winding but we do have current flowing through the conductive chassis/body of the car because all of the electrical components in the car use the chassis as a negative conductor------this flow of current creates a magnetic field within the confines of the car-------any wire that forms a loop within this area will have a current induced into it-----a loop would be defined as a any part of a complete circuit run between two components-----any wire run through this area will have noise if current is flowing in the chassis-------its impossible for it not to have noise-----the goal in a scientific install is to minimize the "loop area" so the noise is below audible levels-----in any system installed in a car with enough gain applied or sensitive enough test equipment there WILL BE NOISE IF CURRENT IS FLOWING IN THE CHASSIS------the larger the loop the more the current and the more loops the more the voltage----------a single RCA run through the car will pick up very little of this noise because the loop area is minimal but it does exist--------a stereo pair of "RCA" will have even more loop area------a comolded pair will have less loop area than a seperate pair of wires------smaller wires will have less loop area than larger wires--------big fat "triple shielded" wires are the worst for noise---------when a pair is run down one side of the car and another pair is run down the other side it is an invitation for disaster since the loop area between opposite sides of the car is gigantic------the best course of action is to keep both pairs of conductors together as close as possible (taping or using loom) so the loop area of the 4 conductors is as small as possible--------of course it varies from car to car depending on actual current paths in the chassis, actual amount of current, vicinity of the wire to the chassis and other factors------BUT the most important thing to understand about this VERY COMMON type of noise is that shielding is TOTALLY ineffective to reduce it---------thats why in the toughest autosound noise cases the quietest wire is extremely small UTP (unshielded twisted pair) as long as there isn't a source of electrostatic noise (such as sparkplug or switching transients) that can only be stopped by shielding----------home stereos don't have this problem since homes are usually made of non conductive wood and we run neutral return conductors for the electric loads-------in homes we have to worry about the actual transformer cores in the individual components, light dimmers etc..........................RC"
Hope this helps, its like being told how to build a watch when asking what time it is, but some of us gotta know "why?!"
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Originally Posted by Allstar3.8T
