Jim Brown, Audio Engineering Society past committee chair on EMI/RFI writes:
Output Wiring is Important Too! It is well known, for example, that RF interference is often coupled
into the output stage of audio equipment – for example, the power amplifiers that feed loudspeakers
or headphones. There is always feedback around that output stage, so RF present at the
output will follow the feedback network to the input of a gain stage, where it will be detected and
amplified. This problem is made much worse when parallel wire cable (zip cord) is used to feed
the loudspeakers or headphones, and can usually be solved simply by replacing the zip cord with a
twisted pair of POC (plain ordinary copper). [Pseudo-scientific advertising hype for exotic cables
notwithstanding, it was shown nearly 30 years ago that #12 copper twisted pair (or #10 for very
long runs) is a nearly ideal loudspeaker cable.] As we will discuss later, the twisting of a pair greatly reduces the
level of RF that the wiring couples to circuitry.
This is from (don't let the title fool you, this started a a audio system paper then he added lots of Ham information.
"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing"
by Jim Brown K9YC
Audio Systems Group, Inc.
Audio Systems Group, Inc. Home Page
Audio Systems Group, Inc. Publications
The basis of this tutorial is a combination of my engineering education, 55 years in ham radio, my
work as vice-chair of the AES Standards Committee working group on EMC, and extensive research
on RFI in the pro audio world where I’ve made my living. That work is documented in technical
papers and tutorials that can be downloaded from the publications section of my website.
more at:
http://www.audiosystemsgroup.com/RFI-Ham.pdf
