This is one of those persistent myths that is frustrating yet ultimately has a basis
Good quality pure silver wire in its raw state sounds wonderfully transparent and
lucid. Compared to copper it simply appears to have less character - a good way to
describe the sound off copper is that it is a little heavy handed, thickening the
tonality of instruments and lacking the lightness of touch of silver. Silver does
not accentuate the treble but does appear to allow greater appreciation of recorded
room acoustics and ambience.
So where does the bright reputation of silver come from?
Firstly many so called silver cables are actually silver plated copper and in my
experience these invariably do have a brightening effect on the sound and commonly
a lack of continuity between the highest registers and the midband. It is this effect
that is often blamed on the skin effect - where high frequencies travel on the outside
of the cable (in this case the silver) and the low frequencies closer to the centre
(the copper). However whilst this does have a sound basis in physics the effect is
normally considered to happen at frequencies way beyond the audio spectrum (above
1 Mhz). Whatever the actual cause, my listening tests show that I prefer not to use
silver plated wire at audio frequencies wherever possible.
There are many different types of silver wire, with varying properties including
levels of impurities. These elements make a substantial difference to the sound.
I only use very pure 99.99% wire in my own wiring but that specification alone is
not the only important one, the annealing process (heat treatment leading to softening
of the wire with benefits including grain growth) is also critical.
Another aspect was one that I stumbled upon quite by chance. The way the wire is
treated during cable construction is remarkably important - allowing the cable to
become stretched during twisting/plaiting for example changes the sound. What’s equally
fascinating is that the burn in effect that is often heard with cables becomes much
more of an issue if the cable is overly stressed and stretched. Quite simply, the
less the wire is worked the better it sounds, so the key is to be very gentle with
it during cable manufacture. I should add that normal handling of wires by an end
user is not in my experience sufficient to cause a problem.
When making speaker cables and interconnects the type of construction, number and
diameter of strands are also terribly important, but this is an area I will leave
open to your own experimentation to avoid giving away all of my trade secrets.
I’ve left possibly the most important aspect to last. The insulator around the wire!
If you look at the properties of various insulators in a text book you will see that
apart from a vacuum (which is a little impractical for cable manufacture), air is
the best insulator. In terms of man made materials PTFE (Teflon) is the next best.
However this is where I will differ from many (but not all cable manufacturers).
Silver wire insulated with PTFE has a brighter and more synthetic sound compared
to an air insulator and spoils the tonality of instruments.
Interestingly some firms (most notably Atlas Cables) are successfully using microporous
PTFE, which has small air filled voids in it, not entirely dissimilar in theory from
using loose fitting Teflon around silver wire, which is exactly what I use for high
voltage applications as the wire is almost completely in air, with just one edge
touching the plastic. This effect isn’t exclusive to PTFE, all plastics exhibit the
same problems to my ear which is why I prefer to use natural materials as insulators
(such as cotton) for audio level connections - the difference is quite remarkable
and it simply appears to ‘get out of the way’ more effectively than most other types
of cable construction.
Some research in France has been carried out which may go some way to describing
this phenomenon, this theory is called ‘Micro Discharge Interface’. This government
funded research took place in 1997 and claims there is intermodulation distortion
of the audio signal caused by high level ultrasound that occurs during transmission
of alternating current signals. It claims the insulator and wire material both appear
critical to reduce this effect to a minimum.
I feel that the microphonics of a cable are also remarkably critical and often over
looked, but this is something I will perhaps leave for another time.