# Surround sound wiring

• posted

I installed wiring for surround sound speakers in an addition I built for a couple and their uncle is upset because I didn't make the two rear connections with exactly the same lenth of wire. He is concerned that the two different lenths of wire will cause a malfunction with the receiver or amplifier. My thoughts are that sound travels fast enough, not to be hindered by fifteen feet of wire. Can anyone shed some light on this situation?

• posted

it would take an extreme difference in length to cause a problem, so much so that it would be most impractical to even simulate. putting that aside, even if there was a miss balance there wouldn't be any malfunction other than maybe the sound not on phase while your listening to it. the only problem you need to worry about is the gauge of the wire on long runs.

• posted

It's not the speed of sound you have to worry about. It is the speed of light, or closer, about 2/3 the speed of light - which is approximately the speed the electrical signal representing the sound travels down typical wires.

Guestimate 200,000,000 meters per second, figure no signals over 40 kHz are meaningful, and do the math. There is no problem if you have a length of wire less than about 1/8th wavelength (ok - I'm really guessing here. 1/2 wavelength difference will switch polarity of the two signals, causing potential cancellation between the two speakers. But if any audiophile can prove he/she can detect 18 degrees phase shift, I'll take back everthing. So, 1/8th (45 degrees shift at frequencies about twice the highest normally heard) should be undetectable.

200,000,000 m/sec X 1/8 X 1/40,000 = 625 meters, or over 2000 ft.

Resistance of the wire enters into the equation way before the signal delay times. I'll leave that analysis to someone else. :)

But, please don't try to squeeze sound waves down those little copper pathways.

-Howard

fr> I installed wiring for surround sound speakers in an addition I built for a

• posted

Even minute phase differences between channels are audible, since they affect the apparent source location. To be on the safe side, reuqire no more than 1 degree phase shift due to cable length difference. This is on the order of phase distortion found in the recording and reproduction amplification chains.

However, assume 20KHz as the highest frequency of interest, anything but a ridiculously huge length difference will still be immaterial.

-- Ron

• posted

Good point, Ron. I'm so much older than stereo, I forgot!

Let's approach it from the time domain:

Assume your ears are 0.2 meters apart. Assume the sound source is 5 meters from your head. Assume the speed of sound at your location is 345 m/sec (ref. Wikipedia)

Now a displacement of 5 degrees of the sound source left or right will create a relative displacement of the source to your ears of +0.00971 and -0.00772 meters, or a total relative displacement of .0174 meters.

Given the speed of sound, that translates to about a 50 microsec displacement.

I'm sure golden-ear audiophiles will claim to be able identify sound sources to a much greater accuracy, but I really could not give a darn if the clarinet section all moved one or two seats to the left.

But, back to wire length. Assuming about 200,000,000 meters/second, 50 usec translates to about 10 km. That backs up what you said, Ron.

Analysis in the phase shift domain at 20 kHz will give different answers, if you assume small acceptible phase shifts. But, the wave length of 20 kHz is so short, (about .017 meters, or 1/10 the distance between your ears) that it is, for all practical purposes, impossible to locate a 20 kHz source with your ears. Have you ever tried to trace the source of, say, a 15kHz squeel?

-My two bits,

-Howard

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