Second topic: cable resistance for analog audio signals.
Cable resistance and the cable driver output (source) impedance work as a voltage divider against the load impedance at the destination receiving the signal.
Most often, the destination is a fixed value and resistive for audio frequencies, such as 10 KOhm or 600 Ohms resistive load.
The cable itself behave as a constant impedance (fixed resistance, capacitance and inductance) so we end up with a constant voltage divider. Even 1000 feet of 18 gauge wire is only 6.4 Ohms (12.8 for a "round trip") which does not cause much loss against 600 Ohms or higher load.
However, speakers are not a constant load. Speakers impedance does vary over the audio frequency range. The speaker designer may attempt to make the end result behave as a constant resistive load, but the end result is often far from constant, and certainly not resistive over the frequency range.
The question is: what is the effect of the varying load impedance (over the frequency range) against the constant cable resistance? This question requires a good model of a speaker. Many such models are available, and vary from speaker to speaker. For the sake of generality, let me simplify the problem to model a speaker as a resistive load. Let me assume a speaker that varies over the frequency range between 3 Ohms and 30 Ohms. The question is: What would such load variations do to flatness response?
Given that we are talking about speaker wire, let us take the following wire gauges (AWG):
00 with diameter of .36 inch
2 with diameter of .25 inch
4 with diameter of .2 inch
6 with diameter of .16 inch
8 with diameter of .13 inch
10 with diameter of .1 inch
12 with diameter of .08 inch
For the 7 wires, the deviation between 3 and 30 Ohm load is plotted below (in dB voltage loss) for distances between 10 and 50 feet of a speaker wire pair.
A 50 feet of 12AWG cable may cause about 0.4db deviation in voltage (.2dB power deviation). The same 12AWG wire at 10 feet length will cause about 0.08dB voltage attenuation (.04dB power). A 10 AWG wire at 20 feet is good for .1dB voltage deviation.
Clearly I am not stating where the deviation occurs, and the argument is built on an assumption that the load varies by a factor of 10 to 1 and is resistive. I will take some time to model the behavior of real speakers, but this ball park exercise shows that the deviations in flatness response due to speaker wire are very small compared to the fluctuations in flatness response of the speakers themselves, where a few db deviations over the frequency range is rather common.
From resistive analysis point of view, for most speakers, a reasonable length (say 20 feet) of 12AWG wire would do very well.
I would not rule out that one can pick differentiate between say 50 feet of 12AWG and 50 feet of say 6AWG. A 0.4dB voltage loss at the frequency where the speaker resistance drops to 3 Ohm may be noticeable in an ABX test. At 20 feet with say 10AWG, the deviation is only .1dB.
The lion share of the problem of deviation from flat response is the speaker itself. The cable resistance is nearly a non issue.
I will post the results of a more accurate model in the near future.
Regards
Dan Lavry
www.lavryengineering.com