Calculation of crosstalk in common ground cable (e.g. 3.5mm)

 Cross talk is roughly the voltage difference made by the resistance of common ground cable.

For example, let's assume AWG 24 1m cable. Single thread of it has R_(CG)=83.4mOhm.

Also let's assume 75dBA listening sound in 105dB/mW, R=47Ohm headphone.

Then, V = 6.856mV = -43dBV = -41dBu 

I = 145.9uA.

The crosstalk = I*R_(CG)/V = R_(CG)/R. (in voltage ratio i.e. dB = 20 log(V/V))

If we aim for -85dB crosstalk in 47ohm headphone, 3.5mm cable must have less than 2.6mOhm.

This is from TI's crosstalk guideline.

83.4mOhm is 32x of 2.6mOhm so -85dB+30dB = -55dB crosstalk in 47ohm headphone with AWG24 1m cable.

One more example. Take best case Silver AWG18 0.5m cable. Cable resistance is 10mOhm. Take 600Ohm headphone. Then the crosstalk is 20log(0.01/600) = -96dB.

Difference between copper and silver is 0.5dB. Best thing to do is to make sure cable thick.