Twisted (was: Re: [sdiy] "Time Winding" in Audio Cables ???)

[JH.]

> Everybody always obsesses about the shield too.  We should just
> remember what the shield is for.  It is a shield against stray
> electric fields, not magnetic fields.

Are you sure? I thought a coax structure is good for electric *and* magnetic
shielding. But it's been a long time since I looked at that.

> That's why we like to
> use balanced lines in studios.  Using a twisted pair that results in
> equal magnetic and electric coupling in both wires of the pair, and
> permits the receiving amp's common mode rejection (either by using a
> transformer or active balanced input) to cancel the coupled signals.
> Actually, the twist is far more important than the shield.

Twisted pair inside a shield is certainly the best solution.
And balanced connection, of course.

I think the problem with magnetic fields and unbalanced coax cables
is not that the coax won't shield the voltage between inner and outer
conductor (differential mode) against the influence of the magnetic field
(I think it does ...), But that the magnetic field will cause common mode
errors along the shield, from one end to the other, the dreaded
ground loops in non-balanced connections.

Does this make sense?

JH.