Originally Posted by JHAz
IMO, absent trable rolloff caused by high capacitance, the only time a cable should have an audible effect is if it is undersized, adding significantly to the effective output impedance of the amplifier.
You seem to have missed the third potential source of audible coloration in speaker wire, being inductance. And the fourth being skin effect.
As practical matters it is very rare for any of the 4 possible sources of treble loss to actually cause an audible difference:
(3) DC resistance
(4) Skin effect of it you will high frequency AC resistance
However, all of them can have measurable effects and under extreme conditions, any might have an audible effect.
And that's only going to make a difference if the amp had a highish output impedance already and the speakers happen to have a difficult to drive (i.e. drops low) impedance.
The output impedance of the amplifier need not be high for speaker wire with high resistance to cause an audible effect. If fine enough and long enough the wire can cause an audible effect all by itself.
For example, 30 gauge wire (hair fine wire) has a resistance of about 0.1 ohm per foot. A 5 foot 30 gauge speaker cable has 1 ohm resistance.
This is the impedance curve of a fairly ordinary reasonably-well designed speaker:
The speaker has a 14 ohm impedance (all resistive) at about 40 Hz. That causes only a 0.7 dB loss. Above about 200 Hz the speaker has an average impedance of about 5 ohms which leads to an loss that is about 1.5 dB. The difference in loss between these two areas leads to a clearly measurable and possibly audible (but probably not) response difference.
Poorly-designed speakers can cause greater response differences. Note that the example is very extreme - nobody in their right mind would use 30 gauge speaker cable. I think the thinnest wire ever sold for the use with speakers is 24 gauge, which has only abouta quarter as much resistance. Of course, if you run a 40 foot 24 gauge speaker cable then things are about twice as bad as my example.