Matching Speaker Wire Lengths

[EdR]

<font color='#000000'>I've heard it both ways about the importance of matching speaker wire lengths.  Now if I remember correctly, the signal propagation speed in copper wire is about a third of the speed of light, or about 3 nanoseconds per foot.

This would seem to imply that if you split a signal from a signal generator, running one directly into a fast oscilloscope and running the other through a hundred feet of speaker wire, then into the scope, and overlaid the two signals, then you'd see about a 300 nanosecond delay between the two regardless of the frequency within the audio range.  This is assuming that other factors didn't preclude you from seeing such a small difference.

Now this would correspond to a frequency in the range of 3 Megahertz, far beyond anything we'd be concerned about for audio work.  If the difference was only ten feet, then it would be more like 30 megahertz.  This would seem to imply that matching the lengths of speaker wire makes no difference at all.

Do I have this right?  Has anyone with a scope tried this?</font>

 

[Rip Van Woofer]

<font color='#000000'>No, I haven't tested it but funny you should ask anyway. There is a discussion of how wire transmits signals on the Elliot Sound forum and a physicist chimed in with this:

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">rough collection of relevent speeds:
 
Speed of a signal propogating on a wire: 2*10^8 m/s (.7 c)
RMS speed of a conduction electron in copper: 10^6 m/s (.003 c)
drift speed of electron current in copper at 1A/mm^2: 0.1 mm/s.
 
For almost any case, only the top number matters.  The others are only relevent if you want to (for instance) derive the resistivity of copper.</td></tr></table>

So, you see, it's even faster at nearly 3/4 the speed of light (.7 c)

Of more concern (I suspect) with speaker wire relative length (maybe the biggest one) is impedance. But I suspect it takes a really gross mismatch to make much of an audible difference there, too. Easy to measure, though.

Elliot Sound forum thread link</font>

 

[Az B]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>

Rip Van Woofer : Of more concern (I suspect) with speaker wire relative length (maybe the biggest one) is impedance. But I suspect it takes a really gross mismatch to make much of an audible difference there, too. Easy to measure, though.

Elliot Sound forum thread link

It depends on the gauge. Larger gauge wire (14AWG+) should see almost imperceptible differences in impedance with realistic lengths.</font>