Speaker Cable Different for 8ohm vs 4ohm

The 4 ohm speakers may draw more current than 8 ohm ones so larger cable and/or shorter runs may help. I have never seen any difference myself with decent speaker cable but could make a difference in some circumstances.

The magnitudes of whatever sonic effects the resistance and inductance of the cable may cause, if any, are dependent on the relation between those parameters and the impedance of the speaker.

The higher the resistance of the cable in relation to the impedance of the speaker, the greater the possibility that it will be sonically significant. The higher the inductive reactance of the cable (the inductive form of impedance, which is directly proportional to frequency) in relation to the impedance of the speaker at high frequencies, the greater the possibility that it will be sonically significant.

Therefore lower speaker impedance makes it more important that cable resistance and inductance be kept low.

Resistance and inductance (as well as capacitance, which is generally a less important parameter for speaker cables but may affect amplifier performance if it is extremely high) are all directly proportional to length.

Regards,
-- Al

A p.s. to my last post.

See this Wikipedia writeup on the voltage divider effect, and in Figure 1 think of Z1 as being the combination of the cable's resistance and inductive reactance, and Z2 as being the impedance of the speaker. That may help clarify why it is the relation between the two that is important.

Regards,
-- Al

So, 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?

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