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by John L. Murphy

Subject:  The Effect of Speaker Cable Lengths

(posted 29Jan01 to Bass List)

C. asked:

> To keep from curling up the speaker wires at one of my speakers, I'd like to
> use unequal speaker wire lengths.  One will be about 10' shorter than the
> other (20'v.30').  Does this really matter?  Am I better off using equal
> lengths and folding up the extra wire?

P. responded:

> Without resorting to mathematics I would guess that 10 feet of 12
> awg wire is about equal to 1 -5 mm of positioning error. Error
> includes movement of head.

Luc then responded:

> Sound = 340 m/s, electromagnetic waves = 300,000,000 m/s or roughly a
> million times faster. 10 feet = 3 m, so the delay accoustically will be
> about 3 millionth of a meter or 0.003 mm. In cables the speed of electrical
> signals is slightly slower due to the insulator having a dielectric constant
> of greater than 1, so maybe the accoustic delay would equal about 4
> thousands of a millimeter. Nothing to be concerned about I think. The
> difference in signal level, because of the extra resistance of the 3 meters
> extra cable, would be much bigger, but also way below the hearing threshold.

I am pleased to report that, using mathematics and physics, I can confirm
Luc's calculations.  A 10 foot difference in the length of a speaker cable
is approximately equivalent to an acoustic delay corresponding to 0.003 mm
of displacement.

Given that a (my) human hair has a diameter of about .05 mm we can conclude
that C. could use speaker cables that differ by MORE than 100 feet (ten
times greater than he asked about) before the cable length difference would
approach the acoustic effect of moving the speaker (or listener) just a
hair's width.  In other words there would be no chance of this ever being
audible...unless you are certain that you can hear the difference in moving
one speaker one tenth of a hair's width.   :-)

But...the difference in DC resistance of C.'s unequal cables might begin
to approach audibility thresholds depending on wire gage and the impedance
characteristics of his speakers.  I still wouldn't worry about it unless
this were a serious research project where the results were intended for
publication and would be subject to (razor sharp) anonymous peer review.

For any of the popular audio magazines, on the other hand, you could say
anything you wanted...mystical explanations are quite welcome in the popular
press as they constitute a smoke screen of disinformation behind which
dishonorable manufacturers hide to sell fantastically over priced products
with a straight face...and buy lots of ad space.  As always, the joke is on
the unsuspecting consumer.

My advice to all audio consumers is to be suspicious of unsubstantiated
advertising claims, ...be VERY suspicious.



John L. Murphy
Physicist/Audio Engineer
True Audio
Check out my recent book "Introduction to Loudspeaker Design" at Amazon.com

Also See:

The Potentially Audible Effect of Speaker Cable Resistance

The Potentially Audible Effect of Speaker Cable Inductance


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