No one actually knows how to lculate what speaker cable they need

Mr. geoffkait

Your say about hearing only the 1/2 wave in AC is not supported by anyone. It is absolutely incorrect.
The only way doing that, is by placing a diode on the line. That will eliminate any current the opposite direction.
If that is done, you will really get only 1/2 the wave, 1/2 the voltage and also 1/2 the power. For sound, you will get 50% distortion.

Showing now the FR swipe on a Spectrum Analyzer, would present a whole different thing than without that diode.
Even the speakers motion, is on both directions (pushing out or pulling in) must be done by a signal (Amp. forced) and not like a door with a spring that close automatically. 

Sorry, if you are an Audioquest sales guy. 
As for power cords, please leave it out. We are talking about speaker cables on this chat. 

None of the above, is on the subject, of how to fit (calculate) the right cable for your system. Unfortunately, Audioquest can't tell you that. 

I mentioned Audioquest since power cords are obviously in an AC circuit. No, I’m not an Audioquest sales guy. Would that make a difference? Do you think Audioquest is lying? I’m talking about all wires, obviously. To be honest, I’m not sure you are understanding what is meant by cable or wire “directionality.” It doesn’t mean wire acts like a diode. What I’m saying, don’t put words in my mouth, is that AC current travels in both directions, but you only need to worry about the current traveling toward the speaker. That’s why reversing speaker cables, interconnects, fuses is audible. And why power cords should be controlled for directionality like any other cable. Even though directional differences in resistance are very small, they are not entirely symmetrical, differences in sound are quite audible and often quite pronounced. Even for a teeny tiny little fuse. This is not my first rodeo. 🤠

Mr. geoffkait
Please don’t worry about any direction of the AC current. They are both well. No other area in electricity (from consumer to space) ever dealth with such a thing as directivity in condutors. In audio, it did. Not because it is any different nor more important (than medical life supporting equipment), but because that crowd is willing to buy that story and pay for it a lot.
There is no such thing, except in audio. Sales guys who take us as NAIVE as it gets.
By the way, if you drink EVIAN mineral water, you might be one of them...