FYI Common Grounds Newer Stereos

[KnottyBuoyz]

I just ran across a situation involving a marine stereo refit. The old boat was wired with a common ground for the rear set of speakers and the fwd set of speakers. In the olden days (1987) when this boat was built it was probably ok or a common practice. The boat had a switch on the dash which disrupted the common ground to shut off the rear speakers.

I wanted to upgrade the stereo with a Jensen 5112 and Remote which I picked up off of e-bay w/4 new speakers for under $200. First time I set it all up using the old wire the speakers would cut out at moderate volume and the unit would overheat. I posted some Q's on another BBS I frequent and got some good info from some audio techs. Here's basically what happened....

Originally Posted by DavidM

You cannot share a common negative between the left and right speaker terminals on modern head units ...they will sense this and shut down when you do this. The reason is that an audio signal is an AC source and there is no phase synchronization between the right and left channels with audio signals...therefore connecting the negative terminals together between the right and left channels would cause problems. I have learned this the hard way. The pos and neg terminals of speakers is only for keeping the speakers in phase with each other..so that none is 180 degrees out of phase with the other. Speakers that are 180 degrees out of phase with each other cause full or partial phase cancellation...basically making them sound like crap, especially at lower frequencies.

Had I not figured it out with help I probably would have ruined the unit. I ran all new speaker wires independently to each speaker and this solved the problem. Trying to trace the old wiring which was pinned between bulkheads and hull was an exercise in futility so new was the best option for me. For a relatively cheap unit (maybe 1 or 2 yrs use out of it before we sell the boat) it'll be fine and sounds pretty good. I especially like the remote at the helm.

FYI

Rick

[Tim B]

Whether you can do it rather depends on way the amp is built. However, if you take a modern push/pull amp, then the black wire going to the speaker is not ground anyway, thus connecting two together is a bad idea.

For op-amps where the output is referenced to 0v. Connecting grounds between speakers will work but it is bad practice.

The easiest solution is to run twin-core cable to each speaker, then connect to the correct +/- on the amp.

There's loads of info on amplifier circuits if you google for them.

Cheers All,

Tim B.