Wiring Home Audio Speakers with Common Ground

[mr_sooty]

Hi, this is not guitar related, but I thought someone here might know the answer.

When setting up my home audio system last night one of the springy clips that holds in the wires broke and I couldn't make a connection for the negative end of the center speaker. I noticed that if I connected the negative wire from the center speaker to one of the other negative inputs the speaker worked. But I also noticed that if I connected it to the sub-woofers negative I got the signals that I would expect to go to the subwoofer - bassy rumbles etc. This seems weird as I would have thought it was the positive that sends those signals and determines what sounds are going to what speaker. This would imply that the negatives are not 'common'. Despite that information, I connected it to the negative of one of the surround speakers. It works but I can't really tell if I'm getting the center speaker signals or the surround signals. Does anybody know if the negatives in a home audio system would be common? I'm a bit fuzzy on the difference between the negative signal of a speaker and the ground of a circuit. It's obviously not just a ground as it makes a spark if you touch the negative wire to the chassis.

[blademaster2]

Although many systems use the power supply negative connection connected to ground (at a single point), and speaker connections also connected there on the negative terminal, I do not think that you can rely on that. Especially battery powered systems might not have this connection and the negative signal is also driven with half of the speaker signal amplitude (this would be a differential output and not single ended), so for those systems connecting the negative speaker output to the ground will short that driven signal out.

Also, seeing sparks is an indicator that these cannot be connected happily.

[reTrEaD]

Jul 24, 2020 9:08:31 GMT -5 blademaster2 said:

Although many systems use the power supply negative connection connected to ground (at a single point), and speaker connections also connected there on the negative terminal, I do not think that you can rely on that.

Agreed.

If you have a schematic, you can determine if the (-) of all speaker connections are tied together. Barring that, you might use an ohmmeter.

'Bridging' outputs, where there are essentially two amplifiers which are 180 degrees out of phase, one for the (+) speaker connection and one for the (-) speaker connection, have become relatively common. Especially so in subwoofer amplifiers. It's entirely possible the amplifier or receiver in question has the (-) speaker connections for the left, right, and center channels all tied to ground and the subwoofer section uses a bridging arrangement. But we don't know that, at this point.