[BC] audio cable termination

[Glen Kippel]

On Jan 5, 2008 7:11 AM, Ron Youvan <ka4inm at tampabay.rr.com> wrote:

>   Terminating any cable also lowers the overall impedances and reduces the
> crosstalk
> from other nearby circuits and RF in general.
>   600 Ohms was also the impedance of the twisted AWG 19 cotton covered
> twisted pairs
> in the original lead covered telephone cables.  I was told it exceeds 900
> Ohms by a
> Verizon engineer with the current AWG 24 (or smaller) with polyethylene
> insulation.
> --
>
I suppose the 600-ohm standard came from the telephone industry, and was
generally adopted by US broadcasters.  I recall reading an article in db
Magazine in the late `60s or early `70s about the European method, using a
really low source impedance and a high impedance on the device being fed.
It was stated that it made it easy to connect several devices to one source,
just like if you want to plug a lamp. toaster and hot plate into one AC
outlet, you just use a cube tap -- you don't worry about
impedance-matching.  So, this has now carried over into products used here,
probably because these same devices are used all over the world now.