high end audio

The Challenge Of Speaker (High Current) Cable Design
While there are many physical, electrical and magnetic phenomena responsible for distortion in cables,
there are really only a few basic mechanisms which account for the majority of the performance variations
between cables. After considering the following information and evaluating even a small variety of
different cable types, you can acquire the ability to look at a cable’s design and know pretty well whether
it deserves your further attention. Please don’t close your mind to new possibilities, just develop an
educated skepticism.
Skin-Effect is one of the most fundamental problems in cables. It is useful to think of a metal conductor
as a rail-guide. Electric potential is transferred as current inside a metal conductor and as a magnetic
field outside the conductor. One cannot exist without the other. The only place that both magnetic field
and current density are 100% is at the surface of a conductor. The magnetic field outside a conductor
diminishes at distances away from the conductor, density is 100% only at the surface of the conductor.
Something similar is true inside the conductor. Skin-effect means that current density diminishes at
distances away from the surface on the inside.
There is some disagreement as to whether skin-effect is relevant at audio frequencies. The argument
concerns whether skin-effect causes damage other than simply power loss. Since the 3dB down point
(50% power loss) for a certain size strand might be at 50,000Hz, not everyone understands the mechanism
by which skin-effect is a problem at audio frequencies (20-20,000Hz). However, the problems are
very real and very audible. This is because well before skin-effect causes a substantial power loss, it
causes changes in resistance and inductance. Skin-effect causes different frequencies to encounter
different electrical values at different distances from the surface of a conductor.
If a single strand is too large, skin-effect will cause each frequency component of an audio signal to
behave differently. Each frequency component will exhibit a unique current density profile. The result
is that some of the delicate high frequency information, the upper harmonics, will be smeared. We
hear sound that is dull, short on detail and has a flat sound stage. The energy is there, the amplitude
(frequency) response has not been changed, however the information content of the signal has been
changed in a way that makes it sound as though the midrange notes have lost their upper harmonics.
There is a textbook equation which describes the reduction in current and power density at any depth
from the surface of an electrical conductor. For copper the equation is: 6.61 divided by the square root
of the frequency (Hz) equals the depth in mm at which the current density will be 1/e. Since 1/e is 37%,
this equation tells us the depth at which the current density has been reduced by 63%. For 20,000Hz,
current density is only 37% at a depth of 0.0467 mm, which is the center of a 0.934 mm (18 awg)
conductor. Conventional use of the above formula falsely assumes that it is acceptable to have a 63%
reduction in current flow and an 86% reduction in power density at the center of a conductor. However,
this formula does not by itself describe at what depth audible distortion begins. Listening (empirical
evidence) shows that audible distortion begins at somewhat lesser depths.
There is a solution to skin-effect-using a single
strand of metal which is just small enough to push
skin-effect induced audible distortion out of the audio
range. Simple evaluation of multiple sizes reveals
that audible skin-effect induced anomalies
begin with a strand (or conductor) larger than 0.8
mm. A much smaller strand yields no benefits but
encourages the problems discussed below.
A common misunderstanding of skin-effect results in the claim that "the bass goes down the fat strands
and the highs go down the little strands." The surface of a fat strand is just as good a path as the surface
of a thin strand, only the fat strands also have a core which conducts differently. In cables with fat
strands which are straight and little strands which take a longer route, the path of least resistance at
higher frequencies is actually the surface of the fat strands. Since the lower frequencies are less subject
to skin effect, they travel everywhere in all the strands.