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in article <1075@grivel.une.oz.au>, scampbe1@metz.une.oz.au (STEPHEN  CAMPBELL) says:
> I'm looking at wiring in my speakers this weekend, and I thought I'd 
> give solid core electical cable a go. My question is, what is the
> optimum cross-sectional area. I've noticed 1mm, 1.5mm, and 12 gauge (2.0 mm)
> all mentioned in previous articles. 
> Is it just a matter of the largest bit of copper you can afford is best ?

Despite a lot of deep misunderstanding of the 'skin effect' there is really
no 'optimum' size for speaker cable.  The skin effect is an electromagnetic
effect that results in non-uniform current density across a conductor as a
function of frequency and material conductivity.

All this means is that beyond a certain thickness, it is pointless making a
conductor thicker for a given frequency because all you're doing is wasting
copper that won't carry much current (ie you won't decrease the end to end
resistance/impedance at that frequency by making the copper fatter).

For pure copper, the skin depth is 14.78 mm at 20 Hz and 0.47 mm at 20 kHz.
This means it is pointless making a conductor of radius greater than 15 mm
for audio because the central part of it won't carry much current at 20 Hz or
higher.

Note that the skin effect does *not* mean that you necessarily lose by making
a cable *thinner*!!!  Making a conductor with a radius less than or equal to
the skin depth means you have essentially uniform current density across the
conductor, hence you're only concerns are the *passives*: inductance,
capacitance, and resistance.

A caveat to that is that the resistance *is* related to the conductor cross
sectional area, but the question you have to ask yourself is what is the
*most* resistance you can get away with?  For a speaker lead, any DC cable
resistance under about 10 milliohm/metre is pretty good and is probably
'transparent' for audio purposes.

For pure copper, that can be achieved with a single conductor of radius of
0.74 mm (area = 1.72 sq mm = 14 gauge??).  Try it.

Once you have low resistance (and there are much cheaper ways of doing that
than by getting Klyster Hyperlitz - just use 12 gauge wire!) then you need to
consider the inductance and capacitance of the cable, and how that interacts
with the speaker impedance.

There is no mystery to that either.  If you can characterise your source and
load, and determine what overall response you want, you can design a cable
with appropriate conductor size, spacing and dielectric (ie passives) to give
you the R, L and C to give you the response you want.

Black Magic cables are a rip-off and take advantage of those who refuse to
accept that electromagnetics in conductors is an extremely well understood
science, especially at ultra-low frequencies (ie audio).  There's no magic
at all.  Dispersion and skin effect issues are irrelevant at audio
frequencies.

It's all just R, L and C.

(Two years ago I did an extensive characterisation of three types of audio
cables.  I can repost it if people are interested).

-- 
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