I couldn't find an impedance curve on the CP6311, but I suspect that its impedance in the top octave either rises to relatively high values, or at least doesn't decrease significantly below the nominal 8 ohm spec. So inductance is probably not all that critical. I'd suggest simply twisting the two conductors together by hand, with three or so twists per foot, and not messing with a drill.
I wouldn't be surprised, though, if the impedance dropped to the vicinity of 4 ohms or so at some frequencies in the bass or mid-bass region, which would tend to increase the importance of having adequate gauge. The resistance of the 20 foot combined length of the two conductors, if they were 18 gauge, would be 0.128 ohms, as can be calculated from this wire gauge table. For frequencies at which the speaker impedance may be in the vicinity of 4 ohms that would reduce your damping factor to 4/0.128 = 31, even if the damping factor of the amplifier were infinite. It could be argued that 31 is more than adequate for this and most speakers, but my instinct would be to increase that somewhat, by going to either 16 or 14 gauge. Those gauges would increase the corresponding damping factor (assuming the amplifier's damping factor is much higher, as it would be for most solid state amps but not for most tube amps) to 50 and 79 respectively.
Enjoy! Regards,
-- Al
I wouldn't be surprised, though, if the impedance dropped to the vicinity of 4 ohms or so at some frequencies in the bass or mid-bass region, which would tend to increase the importance of having adequate gauge. The resistance of the 20 foot combined length of the two conductors, if they were 18 gauge, would be 0.128 ohms, as can be calculated from this wire gauge table. For frequencies at which the speaker impedance may be in the vicinity of 4 ohms that would reduce your damping factor to 4/0.128 = 31, even if the damping factor of the amplifier were infinite. It could be argued that 31 is more than adequate for this and most speakers, but my instinct would be to increase that somewhat, by going to either 16 or 14 gauge. Those gauges would increase the corresponding damping factor (assuming the amplifier's damping factor is much higher, as it would be for most solid state amps but not for most tube amps) to 50 and 79 respectively.
Enjoy! Regards,
-- Al