Speaker Cable Different for 8ohm vs 4ohm

What values of resistance and inductance put a speaker cable in the 'low' category. What measured value should you look for? Also, does that mean good 12 guage is better than a good 14 guage when connecting to a 4 ohm speaker?

12 gauge will have lower resistance, and so it is "better" in that sense. However, depending on the length it may be overkill.

Assuming you want the cable to be as neutral as possible, the basic ideas are that:

1)You want to limit the resistance of the cable to a very small fraction of the minimum impedance of the speaker across the audible frequency range.

2)You want to limit the inductive reactance of the cable to a small fraction of the impedance of the speaker at upper treble frequencies (inductance might be a significant factor at those frequencies, but will not be significant at low frequencies).

Resistance and inductance are both directly proportional to length, as I indicated earlier.

You can calculate resistance from a wire gauge table such as this one. For a 4 ohm speaker I would try to keep the cable resistance in the area of approximately 0.05 ohms or less. That would be the resistance of the cable length x 2, reflecting the total length of both conductors. 0.05 ohms corresponds to the round-trip resistance through both conductors of a 10 foot run of 14 gauge wire.

For a speaker having an impedance of 4 ohms at high frequencies, I would try to keep the inductive reactance of the cable roughly in the area of 0.5 ohms or less at 20kHz, as calculated by the formula 6.28 x 20,000Hz x L, where L is inductance in Henries (for the combined inductance of both conductors in the cable, which is sometimes referred to as the "loop inductance"). A ten foot run of most and perhaps nearly all decent quality speaker cables will meet that requirement. Inductance is more likely to be an issue for speakers such as electrostatics, whose impedance may drop to very low values at high frequencies, and/or for run lengths that are particularly long.

Once those requirements are met, IMO what remains are effects that are pretty much unpredictable and/or unexplainable, that have to be addressed by trial and error.

Regards,
-- Al

Thank you for excellent information. I am using Magnepan 3.6's at the moment with six foot runs of DH Labs Silver Sonic Q-10 Signature biwires. The Q-10's use one run of smaller wire for the tweeter/midrange and a heavier run(12gauge I think) for the woofer connection. I've used this cable for years with no complaints. I believe that it is solid copper with a very thin cover of silver.

I am looking at the new Magnepan 20.7's and if I go there I will have to change the speaker wire since they are not bi-wireable as a result of the new crossover design. Also, I will probably want to extend the speaker cable length to around eight feet. The six foot runs are a bit tight.

I may just go with DH Labs single runs but I am open to sugestions for a really top notch speaker wire that works well with the 20.7's.

I find that using shorter speaker cables lessons the ability of the cables to actually physically reach to the location of my speakers, resulting in a distortion-free, low noise, utter lack of any sound at all.

So that is what a dead short is! I always wondered.

Al, your voltage divider example does clear things up I think.

Let me just clarify one point, is the goal for Vin and Vout to be equal (ie in perfect world where the speaker cable would have no resistance or inductance) such that the voltage output by the amp (Vin) would be the same at driver (Vout)?

Thus in the real world as Z1 increases then for a given Vin the Z2/(Z1+Z2) ratio decreases and reduces the value of Vout.

Thanks