Minimal length of main cable inside the wall

Posted by: graphoman on 20 February 2002

(from an email to the administration:)

Hi Pauls,

I’m going to publish this query on the forum as well but I don’t expect to get any reliable answer since anyone has only one flat so his experience must be limited. Contrary to Naim Audio that is not limited to one particular flat.

My query is that like speaker cable between specially designed amps and speakers (Naim), main cables along and inside the walls of the flat may have a minimum of length necessary to optimal working (impedance?). In my case the outlet for HiFi is in a distance of only some 2 m from the electric meter of the flat so the effective length of the cable is not more than 4 m. Something says to me it’s not enough.

Any opinion?

graphoman

Posted on: 20 February 2002 by Martin Payne

Graphoman,

in this case, less should be more.

You are trying to achieve two things:-

reduce the mains impedance to a practical minimum

reduce interference from other equipment in the house.

You will minimise the former with shorter cable runs.

Keeping runs to your equipment short will also reduce RF pickup over the cable run. Not sure if longer runs might reject some RF from the rest of the house. Anyone any thoughts on this?

I believe some mains cables (e.g. Russ Andrews) may reject mains-bourne RF from the system? I wonder if there is some minimum effective length if this is in use?

cheers, Martin

Posted on: 21 February 2002 by graphoman

thank you but I still argue that common place argument don’t meet this special case.

graphoman

Posted on: 21 February 2002 by Steve B

quote:
In my case the outlet for HiFi is in a distance of only some 2 m from the electric meter of the flat so the effective length of the cable is not more than 4 m. Something says to me it’s not enough

Why is this not enough?

You could extend this arguement and ask "What is the optimum distance from my consumer unit to my local power station?"

I think Martin is right. Less is better, but it's just my opinion and not scientific.

Steve B

Posted on: 21 February 2002 by Martin Payne

quote:
Originally posted by graphoman:
thank you but I still argue that common place argument don’t meet this special case.

graphoman,

hmm, not sure about this argument.

The amps need to see a certain amount of inductance on it's speaker outputs to work well.

The input to the power supply, though, needs to be of the lowest possible impedance. This can be achieved by the shortest cable runs.

cheers, Martin

Posted on: 21 February 2002 by bam

I agree with Martin.

This reminds me of some other thread that I can only vaguely recall. Someone was claiming that RA had suggested that because mains power cable and speaker cable are part of the same power deivery chain you should use speaker cable for your mains. So I suppose it follows that you should use speaker cable back to the substation and then drape it along hundreds of miles of pylons to your nearest power station. Sensible argument if you are a cable manufacturer but otherwise no more than the feeble, cerebral discharge of pond life.

Posted on: 22 February 2002 by graphoman

don’t misunderstand me, I’m thankful for your opinion but I’ll be more thankful for the experience of somebody who did try it. If it were only a matter of electro-technics – well, you know, the Hungarian schoolbooks are just the same like the English ones.

Presently I have the feeling that no matter how long the cable is, I must not use the outlets on the wall behind my HiFi equipment and speakers (that’s the wall in the proximity of the main electric meter of the flat). The treble quality goes bluey and the whole sound picture gets a sleepy character.

I found that I have to take the main from other outlets instead, from other walls of the room. Since it’s rather inconvenient, I think I don’t do it just because of some superstition.

I don’t want to risk any statement of general validity. I only feel that this whole story has something to do with the praxis suggested even by Naim Audio (and others) that main cables and speaker cables must not run parallel.

And I feel that this praxis has (“common sense” it is) nothing to do with the known rules of electro-acoustics: the science.

graphoman