just to make clear, this is mearly a question - i dont have a problem or anything of the sort!

remove the alternator from this equation also...

does DC volts (ie, those supplied around the usual car system) induce EMF into adjacent cables?

i have a limited knowledge on electrics, but from what i do know, EMF is generated on the CHANGE of a voltage (ie: AC volts).

so, why do car ICE installers run the power and speaker wires down opposite sides of the car if the above is true? is it purely down to alternators dont fully irradicate their AC signal fully, and thus showing as alternator whine through speakers?

 

All wires - signal & power have irregularities and minor imperfections in their 'stream'.

Placing them away form one-another reduces the probability that one will interfere with the other.

 

Short explanation is that running massive amounts of power (hundreds of amps of current) through non-shielded wire is capable of inducing current into other adjacent wires (this is EMF - Electro-Magnetic Field/Force/etc.). That current is a varying DC current that is replayed by the speakers as a hum, buzz, etc (voice coil is being magnetized by the induced current, not just the music signal current).

Shielding on a wire (such as RCAs) carries that induced current to ground by intercepting it before it reaches the center conductor, blocking it (or at least most of it) from affecting the low current signal from the source to the amplifier (i.e. center conductor doesn't pick up as much stray current as the shield dissipates most of the stray current to ground, keeping the audio signal clear).

 

as long as you have a current flowing through a conductor, you have emf It does not matter whether it is AC or DC. The plastic little toy cars use a DC motor, remember?

and back to the topic, because you have a varying dc current that is being pulled by your amplifier, you have a varying emf. That emf, which introduces a varying current on adjacent conductors, will then produce varying current in the conductor. Result, you get AC introduced to that conductor (does not matter if it is AC + AC or AC + DC) thus causing whine