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

Remember guys, don't feed the Trolls.......

Any MULTI strand 99.5% pure copper (NOT clad) wire will work.
The thicker the better.  12 gauge and thicker will easily 
handle up to 1000 watts/channel rms with no problems.

Simple rule, the thicker the better, the purer the copper the better.
12/10 gauge & thicker will easily handle up to 1000 watts rms amps 
with no problems.

Simple math. Take into account the power demands of the speakers to achieve the desired SPL. Then the power output of your amplifier, and subtract the two. This gives you the margin that can be lost to resistance in the speaker cable, P=I^2*R. You know the power needed to drive your speakers, and you know the speaker average impedance, which gives you the amount of current by plugging in the power and approximating resistance with average impedance. Take the power margin from above, and thus current value and use the same equation to solve for resistance of the cable. Divide this resistance by the distance in feet to obtain maximum ohms per foot of cable, and go shopping!

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