Cables for high efficiency speakers?

I agree with Stan. I can't envision any reason why high efficiency speakers as a class would be best served by any particular kind of cable. Higher efficiency = less current flowing in the speaker wires, which (assuming everything else is equal) should reduce sensitivity to cable differences if anything.

Regards,
-- Al

I would not use a thick gauge wire because a high efficiency speaker will react adversely to skin effect.

The degree to which skin effect may be audibly significant is controversial and highly debatable.

I don't want to get into a debate on that issue, but I think that the following facts may be relevant to Kenny's selection process:

1)What skin effect essentially does is to increase the impedance of the cable at high frequencies, relative to its impedance at low frequencies. If both impedances are negligibly small in relation to speaker impedance, however, the effect will be negligibly small.

2)Differences in inductance among various cables can be demonstrated by calculation to easily outweigh the effects of skin effect on upper treble frequencies. If the cables being compared have a similar physical configuration and differ only in gauge, the heavier gauge cable will normally have lower inductance.

3)The significance of both effects is dependent on speaker impedance at high frequencies. The higher the speaker impedance, the smaller the effects will be.

The bottom line, IMO: Don't put avoidance of skin effect among your primary selection criteria.

Regards,
-- Al

How do you evaluate/measure skin effect?

It would take me several pages to go through the detailed calculations, but this is a summary of the methodology:

Alternative I:

A)If the cable consists of a single conductor for each leg (plus and minus):

1)Start with a wire gauge table such as this one, which shows, among other things, resistance per unit length for the various gauges.

2)Calculate the total resistance for the length of the cable multiplied by 2, reflecting the two-way round-trip that the signal has to make.

3)Calculate the corresponding signal attenuation at 20kHz (that would occur in the absence of skin effect), which (as a worst case approximation) will be dependent on the ratio of total cable resistance to the sum of total cable resistance and the impedance of the speaker at 20kHz.

4)As explained in this reference, make the simplifying approximation that the skin depth that will be utilized by high frequency signal components is equal to the depth at which the current density of the highest frequency of interest (20kHz) is attenuated to 37% of its value at the surface, which for copper at an exaggeratedly worst case temperature of 70 degC is in turn equal to 2837/(square root of 20000 Hz) = 0.02 inches.

5)Calculate the cross-sectional area of the conductor.

6)Calculate the cross-sectional area of the central part of the conductor that is bounded by the effective skin depth.

7)Subtract no. 6 from no. 5 to get the approximate cross-sectional area that will be utilized by the 20kHz signal.

8)Using the wire gauge table, calculate the resistance of the gauge that corresponds to the cross-sectional area calculated in no. 7.

9)Calculate the resulting signal attenuation at 20kHz, which (as a worst case approximation) will be dependent on the ratio of the cable resistance calculated in no. 8 to the total of that figure and the impedance of the speaker at 20kHz.

10)Subtract the number of db calculated in no. 3 from the number of db calculated in no. 9. The result will be a reasonable approximation of the high frequency loss due to skin effect.

B)If the cable consists of multiple individually insulated conductors, that are all equal in gauge:

The calculations are similar to those described above, except that resistances are first calculated for one of the individually insulated conductors, and the two resulting resistance numbers are then divided by the total number of conductors to get the overall resistances.

C)If the cable consists of multiple individually insulated conductors, that are not equal in gauge:

The calculation is similar to (B) above, except that the resistances of the multiple conductors combine as the reciprocal of the sum of the reciprocals of the individual resistances.

Alternative II:

Don't bother with any of the above and accept various published statements, by people who should know, that under typical circumstances skin effect losses at 20kHz will be on the order of a fraction of a db, and considerably less at lower treble frequencies.

Regards,
-- Al

If not a single conductor then must go with Alternative II?

No, I was not implying that. The calculations for cables that employ multiple separately insulated conductors just become a bit more complex, as I described.

BTW, cables that employ that type of construction, typically in sophisticated braided patterns, will usually have much lower inductance than cables that have only a single conductor in each leg (whether solid core or stranded). If the cable length is long and the impedance of the speaker at high frequencies is on the low side, the low inductance resulting from that type of construction will be far more likely to be beneficial to high frequency extension than minimizing skin effect would be, IMO.

On the other hand if speaker impedance at high frequencies is high, and the cable length is short, I doubt that either effect would be significant. And of course improved high frequency extension may not always be subjectively preferable, depending on the rest of the system, the room, the source material, and the listener.

Regards,
-- Al