Why is high capacitance good?

To get rid of any negative effects of capacitance, inductance etc - Spectron Audio use "Remote Sense" speaker cables, see - http://spectronaudio.com/cables.htm.

Basically they take full advantage of their ultrafast feedback loop and include speaker cable into it - making amp/speaker the single amplification system.

Does anybody else use the same concept?

Thank you

Al- thanks for the detailed (and fascinating) response. How high are radio frequencies that you mention? Some of these particular cables may actually attenuate high frequencies (MIT with Wilson seems to be a popular combination because of it) so perhaps you are right.

KeithR

Hi Keith,

RF transmission line effects, including characteristic impedance and vswr/reflection effects due to impedance mismatches, become significant when the length of the cable becomes a "significant" fraction of the wavelength of the signal (which is inversely proportional to frequency).

What is "significant" is a matter of degree, of course, and depends on the particular application, and for audio it would seem appropriate to define tolerances more tightly than for most other applications.

But to provide some perspective, the wavelength of a 20,000Hz signal propagating through a wire is in the rough vicinity of 6 miles. The wavelength of a 20Hz signal propagating through a wire is in the rough vicinity of 6,000 miles. The length of a typical speaker cable would certainly seem to be utterly insignificant in relation to those numbers.

The long-wave radio band is commonly thought of as beginning at around 150kHz, so it might be reasonable to consider some point between say 50 and 150kHz as a conservatively drawn point of demarcation between rf and ultrasonic frequencies. Long-wave transmitting antennas, btw, are HUGE, due to the long wavelengths they are transmitting.

DIGITAL audio signals, btw, have frequency components that extend well into the rf range, and rf transmission line issues are therefore very much applicable to connections between transports or other digital sources and dacs.

Best regards,
-- Al

Hi capacitance cables may be used to 'tune' a too bright system. Too bright a system may be fixed in other ways.

I think that's a bad approach. I personally try to find low capacitance cables, when such spec's are known.
Many cable companies don't advertise such things, do they?

Hi capacitance cables may be used to 'tune' a too bright system.

That is true in the case of interconnects, especially if the output impedance of the component driving the cable is high. It is not true, though, for speaker cables, at least to the extent that cable effects are explainable by generally recognized science (and assuming that the cable does not include a network box of unknown design).

The reason that interconnect cable capacitance can roll off high frequencies is that it interacts with the output impedance of the component driving the cable to form an RC low pass filter (the "R" term corresponding to the output impedance, and the "C" to the total capacitance of the cable). The 3-db bandwidth of the filter (the frequency at which the signal is attenuated by 3db relative to its amplitude at low frequencies) equals 1/(2 x pi x R x C).

In the case of a power amplifier, output impedance is near zero (a small fraction of an ohm for solid state amps, and at most a few ohms for nearly all tube amps), so that effect will not be significant for audible frequencies.

High inductance in a speaker cable, on the other hand, can reduce brightness to some degree, by introducing an impedance that rises at high frequencies and that is in series with the speaker impedance. The inductance of even an average cable can have that effect, if cable length is long and speaker impedance at high frequencies is low.

Best regards,
-- Al