What are the implications of 3 speakers sharing a ground? I know there is different potential for each speaker, but is it possible and/or practical to run an LCR off 4 conductors?

AFAIK this is not possible.  The receiver will surely go into protection.

It's possible, it's practical if you can't run any more conductors, and it's a bad idea.

Let's say each speaker has, for a moment in time, five volts across it. Let's say each speaker wire, ground included, has one ohm resistance and the speaker is an eight ohm speaker.

You'll have five volts going through 1 + 8 ohms, three times, in parallel. That fourth wire, though, conducts the current of all three speakers. Since it will share equally (in this case), we can call it three wires, each three ohms, in parallel, but each wire in series with a speaker.

Thus we have 1 + 8 + 3 ohms as each channel. Not really that bad, though each speaker will only see 3/4 of each voltage. In this example. Ohmage will likely be lower, so this will have less effect than it looks like.

However, that point where all three speakers join together has an odd characteristic: it's at zero volts when no signal flows. Put five volts on one speaker and it's... let's figure... 1 + 8 + 1 = 10 ohms, so that point will be at 0.5 volts. Let's put 5 volts onto two speakers; we'll have 1 + 8 two times, in parallel, or effectively 4.5 ohms, in series with the 1 ohm ground return. That places that point at 4.5/5 times 5 volts, or 0.9 volts.* In other words, adding a signal at the second speaker caused the ground return of the first speaker to change voltage. Thus a signal of the second speaker changed the first speaker's signal.

This is a cool way to introduce less separation and a kind of modulation distortion. It won't sound like distortion in the sense of clipping or noise, but the levels coming out of the speakers will be wrong and will vary in their wrongitude depending directly on the signals fed to the other speakers.

This will not introduce this problem if all speakers have the same signal.

Do it if you have to. Remember that the ground lead will now be effectively a smaller wire if the other speakers all play at the same time.


*I didn't think that through thoroughly. The idea is right but the voltage may be slightly off.

No, it won't. The negative posts are common and have been for decades on anything that doesn't use output transformers or totally discreet amplifier channels. Technically, it's not the best way to do it because the negative conductor is carrying the current from all channels, but it will work.

Using this scheme for an LCR speaker could make it sound odd but protection shouldn't be an issue.

So that lends the question, if the negative posts are electrically common internally, why would it matter if this is done externally?

Well, when it's done externally, there is a significant distance through which the line is shared. Resistance is proportional to distance so only comes into play when the shared path is long (i.e. External.). I may have no idea what I'm talking about.

crosen, you're right. When separate ground leads are used, there cannot be interaction among the speakers due to the ground voltage varying, as the chassis and wire leads to the common are very low resistance in the chassis. Now, if the original poster had told us that he had three #14 conductors* and one #8 conductor, I'd have zero problems with that! We were left to make the reasonable jump that all conductors are the same gauge.


*I originally typed $14 -- that was a funny typo to look at!

I think alot of guys confuse ground with a common.

The wire is indeed 14/4. Thanks for everybody's input on the matter.

Funny this thread is here right now...just today I looked at someone elses install of 4 outdoor rock speakers....4 wires come from house (nuvo system) to utility area behind pool. Those 4 wires are doubled up, in other words 2 wires into 1 (2 conductor speaker wire) and same with the other 2. Then those 2 wires run about 10-15 ' and then split back into 2 wires.... wtf? Bueller...Bueller...

Zohan,
my most baffling case in the eighties was a similar thing. A customer brought in a turntable from which he was not getting any audio.

I looked it over; all looked good, except that he had lengthened the wiring. I checked that out.

To lengthen the audio cables he had cut the phono signal wires and the ground -- that's two hots, two shields and the chassis ground -- stripped all of them back, twisted them together and soldered them to a length of about #12 single conductor stranded wire. Because he wanted this to work, he dutifully soldered the other end of the #12 to all five conductors.

I was too puzzled and amazed to even laugh!

You can try but I do not believe it will work.

I repaired audio amps and receivers in the 70's through about 2000. A two channel amp was almost always common grounded (left and right grounds tied together) and also connected to the chassis. A few exceptions were some of the cheap Kenwoods that put the speakers in series when A+B speakers were selected.

When 5 and 7 channel amps started appearing, the common ground configuration seemed to disappear.

If you tie together three amps that are normally not connected, I would expect the amp to shut down - perhaps not at lowest volume, but likely when you turn it up and some current starts to flow.

Let us know how the experiment works out.

It will work fine, there could be some side effects, but will be the most part undetectable. Fine for distributed audio or typical theaters? Sure. Fine for a high end system, no.

Also be careful, not all amplifiers' negative leads are ground potential. Some amps, such as Pass Labs amps as one example, run fully differential, so the negative lead is in fact an inverted phase amplified channel. Also if you bridge an amp, then that too creates the same situation.

Something makes me think this is not high end.

No.

Ernie may have a lot to say, and it's always interesting to read, but that does not change the answer.

The answer to your question is NO.