Re: James Randi Posts $1M Award On Speaker Cables

On Fri, 05 Oct 2007 23:28:54 -0700, Jeff Liebermann <jeffl@xxxxxxxxxx>
wrote:

ChairmanOfTheBored <RUBored@xxxxxxxxxxxxxxx> hath wroth:

On Fri, 05 Oct 2007 08:12:26 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Fri, 05 Oct 2007 03:45:17 -0700, ChairmanOfTheBored
<RUBored@xxxxxxxxxxxxxxx> wrote:

On Thu, 04 Oct 2007 22:02:11 -0700, Jeff Liebermann
<jeffl@xxxxxxxxxxxxxxxxxxxxxx> wrote:

Silver plated for reduced skin effect? Great for RF frequencies, but
kinda useless for audio, where the skin depth is about 8 mm at 100Hz.
I don't think anyone can afford 8mm of silver plating thickness.
<http://en.wikipedia.org/wiki/Skin_depth>

I don't need a primer on the subject.


It has nothing to do with skin effect. Silver conducts better. D'oh!

The ohms per foot is lower. Lower is better in this realm.

The plating is micro-inches on top of a copper wire that's mils in
diameter. And silver conducts only a little better than copper. So the
net effect of silver plating on wire resistance is unmeasurable.

Absolutely incorrect.

There are no absolutes. Everything is relative.

SPC has a lower resistance than bare copper or TPC. It is right there
in the specs.

SPC? TPC?
11th Commandment: Thou shalt not abrev.

Specs? Where?

Let us grind some numbers. From:
<http://www.epanorama.net/documents/wiring/wire_resistance.html>
Resistivities at room temp:
Element Electrical resistivity (microohm-cm)
Aluminum 2.655
Copper 1.678
Gold 2.24
Silver 1.586
Platinum 10.5

That makes silver slightly better than copper or:
(1.678 - 1.586) / 1.678 = 5.5% better
However, that assume we're comparing equal amount of silver and
copper. With silver plated 12AWG copper speaker wire, there's
considerably more copper wire than silver plating.

Grinding some more, 12AWG copper (solid) wire has a cross sectional
area of 2.053 square millimeters for a radius of:
2.053 mm^2 / Pi * r^2
r = 2.54 mm radius

Assuming a typical silver plating layer, but as thick as possible, of
50 micro inches or 0.00127 mm of silver plate. That's a cross
sectional area of:
Area = Pi * (r2 - r1)^2 = 3.14 * ((2.54 + .00127) - 2.54)^2
Area = 3.14 * .00127^2 = 0.00001 sq mm silver

That's about 2.053 / 0.00001 = 200,000 times more copper than silver
for 12AWG solid wired based on cross sectional area.

I'm too lazy to work out the parallel resistance of the silver plating
and the base copper. Suffice to say that 0.00001 sq mm of silver is
not going to have much of an effect on the resitance of 2.05 sq mm of
copper, when the resistivity is only 5% different. If we switch to
stranded wire, there will be some more silver plating, but not enough
to make much of a difference. (It's also almost midnight and my brain
is rapidly turning to mush.)


Since silver only conducts 5% better than copper, most of the
reduction in resistivity results from the silver plating simply
increasing the diameter of the wire a tiny bit. In the case of #12,
the diameter increased from 80,000 uin to 80100 uin, ratio 1.00125, so
the area increased by 1.0025, so the conductivity improves by about
0.25%, not too impressive when you consider that the tc will be 0.4%
per degree C.

For fine-strand wire the plating is relatively thicker so the effect
is larger. But wire manufacturers are no fools, and I wouldn't be
surprised if the draw the copper a bit smaller when they know that
they're going to plate it back up.

Since copper is a lot cheaper than silver, if you want conductiviry,
buy bigger wire.

John


.

Relevant Pages

  • Re: Surprises about electrical conductivity
    ... It was copper, not plated with anything. ... indeed 9 or 10 gage solid copper wire. ... The bridge was part of the test board, where the test guys could patch into the various circuits - and isolate them from traffic. ... If it *is* silver, it is a marvelous idea, because sposedly the bulk of the current density in a conducting wire lies on the surface of the wire. ...
    (rec.crafts.metalworking)
  • Re: James Randi Posts $1M Award On Speaker Cables
    ... I don't think anyone can afford 8mm of silver plating thickness. ... And silver conducts only a little better than copper. ... net effect of silver plating on wire resistance is unmeasurable. ...
    (sci.electronics.design)
  • Re: diff in coils between c_poise and vertload ??
    ... My point was more about the effects of copper oxide on inductor Q. It ... silver will form all those salts. ... since silver has the highest conductivity of all metals. ... Chipman is obviously assuming a pure silver plating. ...
    (rec.radio.amateur.antenna)
  • Re: diff in coils between c_poise and vertload ??
    ... My point was more about the effects of copper oxide on inductor Q. It makes me think that the best way to prevent the build up of oxide is to use some kind of low-loss insulating material on the surface of the copper. ... silver will form all those salts. ... "For many years it was thought that silver was necessarily the best plating material, since silver has the highest conductivity of all metals. ... Chipman is obviously assuming a pure silver plating. ...
    (rec.radio.amateur.antenna)
  • Re: James Randi Posts $1M Award On Speaker Cables
    ... where the skin depth is about 8 mm at 100Hz. ... I don't think anyone can afford 8mm of silver plating thickness. ... And silver conducts only a little better than copper. ... net effect of silver plating on wire resistance is unmeasurable. ...
    (sci.electronics.design)
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