[RFI] NOISE GADGETS

[Jim Brown]

First, audio cables are too short and the wavelengths of audio signals too long for 
transmission line behavior of audio cables to be a factor. The mfrs of exotic cables 
would have you believe that is not true, and engage in all sorts of gobbledegook and 
double-talk to sell their snake oil.

Second, the only factors about audio cable that DO apply are those you would expect 
from thinking through the basic physics.  

1) you want cables to be as "beefy" as possible if you want good solid bass. This is the 
old "damping factor" issue. If the resistance between the power amp and the woofer is 
very low, the amplifier controls the woofer and you get solid bass. If the resistance is 
high, the woofer flops around on its own and the bass is mushy.  There is an excellent 
AES paper by Prof Emeritus Richard Greiner (U of Wis at Madison) that studied a 
bunch of the exotic cables and found their benefits to be non-existent, with a single very 
special exception that applies ONLY with a very unique and rarely used type of 
loudspeaker. You can download his paper from the AES website, and you can find it in 
any decent EE library that has back issues of the Journal of the AES. 

2) You want ALL audio cables, including loudspeaker cables, to be twisted pairs. Why?  
Again, the laws of physics tell us that twisted pair cable helps reject external fields, 
including both low frequency magnetic fields and high frequency radio interference. It is 
quite well known that parallel wire cable is quite effective at coupling RF into power 
amps, and once inside, the feedback loop couples it to an earlier stage where it is 
detected.  Simply replacing what is really nothing more than glorified zip cord with 
twisted pair cable cures a LOT of RFI problems.  Magnetic coupling is a big deal with 
power line stuff getting into line level and mic level signals, but rarely with loudspeaker 
wiring. But RF getting into loudspeaker wiring is a VERY common problem if the audio 
gear is around big transmitters (or very close to smaller ones), and it's a problem from 
the AM broadcast band all the way up through VHF-TV frequencies. Why is this a 
problem with loudspeaker level signals?  Simply because a lot of audio designers don't 
think about or understand RF and avoiding RFI. 

It's quite interesting that almost none of the exotic cables are twisted pairs. Prof Greiner 
found that twisted pairs of POC (Plain, Ordinary Copper) were as good as any of the 
exotic loudspeaker cables of equal wire gauge, with that single very special exception 
(and it was a twisted pair). 

You can download and read a lot of great practical info about audio wiring and 
interconnections from the Jensen Transformers website, all written by Bill Whitlock. 

Jim Brown K9YC

On Tue, 9 Nov 2004 14:17:24 -0700, Howard Lester wrote:

>Jim,
>
>For my own edification... I've never believed in any of this "Monster Cable"
>nonsense from the first day it was put on the market.  We know that, with
>RF, coax cable exhibits greater losses the higher the frequency, the longer
>the transmission line, and the worse the SWR. Thinking along similar lines
>(if one can compare RF to AF), how are audio frequencies affected by the
>cables used?
>
>Howard Lester N7SO
>Tucson, AZ
>
>----- Original Message ----- 
>From: "Jim Brown" <jim at audiosystemsgroup.com>
>To: <rfi at contesting.com>
>Sent: Tuesday, November 09, 2004 1:47 PM
>Subject: RE: [RFI] NOISE GADGETS
>
>
>> On Tue, 9 Nov 2004 13:01:10 -0600, EDWARDS, EDDIE J wrote:
>>
>> >It reminds me of the whole "Monster Cable" industry.  Now that's a
>> >rip-off.  Then again, I'm not an audio guy so what do I know.
>>
>> Ah, but you understand the laws of physics rather well!  You've correctly
>identified it as
>> 100% serpent lubricant.
>>
>> Jim
>