Why is high capacitance good?

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

Superb post Al.
Learnt a lot.

Al, I have heard that it is always best to keep the speaker cables as short as possible even if it means one has to use longer interconnects to get the power amp closer to the speaker. What is your take on this ? I always thought since IC carries low level signal it should be kept short (especially RCA based IC), but the general thought is opposite. I am sure there must be a scientific explanation for this as well. Please shed some light.

Also, how long an IC is okay to use in a decent hi-rez setup ?

Thanks, Pani!

As you probably realize, there is no one right answer to your questions, because there are many system-dependent variables involved. And as you've probably seen, there have been lots of inconclusive debates on those questions, here and elsewhere. But following are some general guidelines, as I see it.

First, keep in mind that overall system synergy can sometimes be best served by cabling that functions in a non-neutral manner. But assuming that neutrality is the goal:

1)The likelihood that long interconnects will function in a neutral manner is increased if:

-- The interface is balanced (xlr's).
-- Cable capacitance is low.
-- The output impedance of the component driving the cable is low, particularly at high frequencies. (Having low output impedance at low and mid frequencies, as well as at high frequencies, can be important in relation to the input impedance of the destination component, but that is a separate issue).
-- The resistance of the cable shield (or other signal return connection) is low, particularly for rca cables. That is something that is not usually specified, but figures to have some degree of correlation with the overall quality of the cable.

2)The likelihood that long speaker cables will function in a neutral manner is increased if:

-- Resistance is low.
-- Inductance is low.
-- Speaker impedance is high.
-- The speaker is capable of sounding good with an amplifier that does not have a high damping factor. A speaker which is tube amp friendly will generally meet that criterion, irrespective of whether it is actually being used with a tube amp.

Best regards,
-- Al