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

Mr. stevecham
I would not recomand of a "1 inch square (cross sectioned), or other rectangular profile, six nines, pure copper bars". It is not flexible at all. What is your guide to end up with that kind of wire? What amp, speaker and distance?
Getting a thicker than 12-14 AWG connected to the amp and peaker, requires a short wire that would fit into a banana plug.
Ther are such, that can use up to an 8 AWG wire (better than 12-14 AWG).
Such ending, can be done for up to 4xo AWG (214 mm2 = 0.33170066340133 sq in). Thats a lot!

@steve cham -- true.  But if the solder or soldered connector  brittle, cracked or oxidized, the pins are oxidized or wobbly, or the metal mismatched then you can get plenty of degradation in sound.  It's happened to me and some serious  pros in a neurobiology lab.  Tens of dollars isn't going to beggar anyone.

Mr. maplegrovemusic
Thanks. They do not get specific, of what that resistance is or what is the cable length. 
However, digital amplification (D class) have a different nature of it's output model (electronics) than A/B Class amplifiers, that are most common. 
Tube amplification is also very different, mostly have high output resistance (relatively to A/B class) or low DF.
Athe calcualtion also do not apply to non coil speakers (as ribbon or electrostatic).

I have tried many cables to drive modified Magnepan MG IIIa’s with a Pass Labs 250.5.  The best so far are DIY five foot cables made with 16AWG .999 pure solid silver inside 1/4” poly sleeve connected directly without termination to amp and speakers.  The two leads per side are keep 2 1/2” apart from each other in a ladder design.  Every 12” a three each piece of plastic plumbers strap is fixed to the cables with zip ties to keep the cables apart.  Total cost: under $7 per foot ($70 for for two five foot cables).  The sound is holographic.  Best bass these speakers have ever produced.  Very revealing mids and highs, particularly with DSD recordings.

Happy listening.