Not only am I confused about voltage of an audio signal but I just learned that the resistance of copper wire changes as the frequency of the signal changes.
This from bluejeanscable is interesting:
One of the most common misconceptions we run into, on the subject of resistance, is that resistance is somehow irrelevant to audio and video signals because those signals are alternating current (AC), and a wire's resistance is expressed as "DC resistance," which refers, of course, to direct current, not alternating current. So, we are often asked, if resistance is DC but the signal is AC, what could resistance have to do with anything?
Resistance acts upon both alternating current and direct current. The reason resistance is expressed as "DC resistance" on spec sheets is not that resistance is not applicable to alternating current. Rather, it's because of something called "skin effect." As the frequency of a signal increases, the current flow in a wire concentrates toward the outside, or "skin," of the conductor. This means that for any given wire, if we measure resistance at different frequencies, we'll find that the resistance increases with frequency. Resistance is expressed in spec sheets as "DC resistance" because the resistance value of one wire at DC can be meaningfully compared to the resistance of any other wire at DC. In theory, if one wanted to do so, one could specify the resistance of wires at any frequency; we could make up tables of "1 MHz resistance" instead of DC resistance. This isn't done because (1) there isn't any handy "reference" frequency which is broadly applicable to all uses of wire, and (2) it's harder to measure resistance properly at higher frequencies because it is difficult to separate out losses to other factors which become relevant as frequency increases, like capacitance, inductance, and return loss. But make no mistake: resistance converts electricity to heat in a wire regardless of whether the electricity is DC or AC. And, by the way: in the case of a stranded wire, the "skin" in question is still the outside of the bundle; it is not, as people often assume, the skin of each individual strand.