User Manual

CABLE THEORY

Page 9

is not much penalty. On the other hand, inductance is always a problem-a constantly accumulating

problem. Capacitance and inductance are not the only important variables in cable design. However,

it is productive to create cables whose capacitance doesn’t “go over the cliff” while also designing for

minimum inductance.

One theory of cable design holds that the characteristic impedance of a cable should match the imped-

ance of the loudspeaker (When an antenna cable is referred to as 75 or 300, that is the characteristic

impedance). Impedance matching is a valid concept which only applies when the impedance of the

source, the cable and the load are all the same, and when the cable is longer than the wavelengths

of the frequencies to be transmitted. Ampliers do not have 4 or 8 ohm output impedances, in fact

amplier designers try to have as low an output impedance as possible. Speakers are all different and

never have the same impedance at all audio frequencies. Since characteristic impedance equals the

square root of the ratio of inductance to capacitance, very high (over the cliff) capacitance is a neces-

sary corollary of a low characteristic impedance. Such high capacitance can severely affect amplier

performance and should be avoided.

Some of the rst generation of specialty speaker cables had a characteristic impedance of about 8.

These very high capacitance cables sounded better or worse because of their ability or inability to deal

with the problems discussed earlier. However, many of these cables were accused of being extremely

bright and irritating. It was not the cables which were so bright, it was the sound of the amplier,which

had been encouraged into instability by the cables.

Such false conclusions could be avoided if products were judged on their merit and then methodically

analyzed. Consumers, store buyers, and reviewers each need to discover what sounds good. Unfortu-

nately the desire to understand “why” can cause more confusion than insight if not pursued empirically

as well as theoretically.

The Challenge Of Interconnect (Low-Current) Cable Design

If you haven’t read the previous discussion of problems in speaker

cables, then please read that rst. The following is meant to build

on that foundation. The same problems exist in both high-current

(speaker) and low-current (interconnect) applications. However, the

hierarchy among these problems differs.

In low-current cables; skin-effect, electrical interaction, magnetic in-

teraction and conductor quality are still primary problems. The nega-

tive sonic effect of internal mechanical modulation due to magnetic

elds is greatly reduced.

The electrical behavior of the dielectric (insulating material) is much

more important in low level cables. Dielectric involvement (the way

in which a particular material absorbs and releases energy), has a

profound effect on an audio or video signal. Dielectric constant, the most often quoted specication for

insulating material, is actually not very helpful in understanding the audible attributes of different materi-

als. The coefcient of absorption value is more relevant, and the dissipation factor and the velocity of

propagation are even more useful.

The problem is that any insulating material next to a conductor acts like a capacitor which stores and