Newsgroups: comp.dcom.cabling
Subject: Re: Coaxial vs CAT 5
References: <[email protected]>   <[email protected]>   
Robert Redelmeier  writes:

> James Knott  wrote:
> > One thing pointed out by Larry Klien, was that for most
> > purposes, ordinary lamp cord was fine for connecting speakers.
> > Anything else is a waste of money. 
> 
> It is.  

You are right on this. 

> My slight concern with lampcord is it can pick up 60 Hz
> hum from any nearby powerfeeds (even in wall).  So it should be
> kept away from power, cross at right angles or be lazy-twisted.

You shoud no concern much on this. 
Even a normal lamp cord used as speaker cord is very resistant 
to nearby powerfeed interference. The reason for this is 
that the speaker circuit is very low impedance circuit 
(amplifier sub ohm impedance, speaker 4-8 ohms). This kind 
of low impedance circuit is very resitant to outside interference 
pickup when wired with cable where the wires are quite near 
to each other (does not need to be twisted pair, just wire pair). 
The noise picked up by this kind of wire from external sources 
(electric and magnetic fields) becomes mainly common mode 
noise, which gets canceled by the floatign speaker load 
(speaker reacts only to differential signal between speaker wires). 
And the last thing is quite lof efficiencly of speakers 
quarantee that even if some microwatts gets coupled to 
the wire, those low power cannot generate audible amount of noise. 
This is the normal case. 

Generally unless you put the speaker wires to the same bundle 
with the high current carrying power wires, you don't have 
to worry about interference problems, at least on 60 Hz interference. 
And generally even if you have the amplifier power and speaker 
wires as one wire bundle, you generally do not get any problems.

If you have something to worry with speaker wire noise 
pickup, that problem is most often RFI. The speaker wires 
can pick up RF interferences. It is very rare that the 
amoput of RF picked up by the speaker wire itself could 
make much noise to the speakers. The bigger problem is 
that the RFI can get through the speaker wires to inside 
amplifier, near noise sensitive parts. There the RFI 
can cause all kinds of cross modulation products, 
can get demodulated and amplified etc.. The results 
of those problems when amplified by the amplifier 
electronics can sometimes be heard. The problem 
can be seen when you are near radio transitter and 
the amplifier you use is not well shielded against 
interference. Typical problems that canbe heard are noise 
humming/buzzing noise when using GMS cellular phone near 
speaker wiring or "click" noise when pressing "talk" button 
on walkie-talkie radio near stereo equipment.

> > However I'd suspect using telephone cable or CAT 5 might
> > have resistance loss issues, when handling low impedance
> > loads, over significant distances. 
> It does.  Do not use Cat5 for low-ohm speakers if you want
> decent volume.

You are right on this. 

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/