--- In Mike Feldman
<> wrote:
> Rich Peet wrote:
>
> > I have read the stuff they wrote, but for the configuration of
inner
> > wires to matter that means that the shield already has failed and
> > what you needed was a better shield. And so, I don't buy into
their
> > sales stuff on reverse twisting.
>
> My understanding is that it protects against noise currents
> induced by magnetic fields, whereas the shielding keeps out
> electric fields. Why add mu-metal to the cable when geometry
> will do?
>
The 4 conductors in the twisted "star" pattern provides more physical
symmetry of the signal-carrying conductors; this symmetry means that
signals induced along the cable are more completely cancelled out by a
differential input.
About 16 or so years ago I was at an AES talk given by consultant Neil
Muncy (bio: http://recordist.com/ampex/biographies/muncybio.html) on
studio wiring and grounding. In one of his demonstrations he was using
a cheap AC power drill to induce noise into various pieces of mic
cable that I believe were terminated with a typical mic impedance on
one end, and connected to a mic preamp on the other. Inducing into
single lengths of the cable, the star-quad was alot quieter than the
other 2-wire types. He then proceeded to wind a few turns of the mic
cable around the drill; the induced noise in star-quad was quite low
while all the others were rip-your-face-off loud.
Anyway that convinced me that star-quad would be the cable to use in
the most demanding environments. Obviously most nature recording
venues are not usually so hostile.
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