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


It goes back to cable manufaturars, mostly provide no relevant data! to sales and the users. None will answer this!
Whay do you think that you own now the optimal cable to your setup?
I think I've figured it out. 


128x128b4icu
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b4icu- Here is a link to a interview with a amp designer. At the 22 minute mark he discusses they have designed a speaker cable that is the correct impedance for their Ion digital amplifier . Your statement above and now watching this video , this is the first I have ever heard anyone mention this . You are onto something here . 


https://www.dagogo.com/exogal-interview/
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!
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@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.