As I understand it, the black speaker terminals on the amplifier are all “common,” or connected internally, and only the red terminal is unique to each speaker. In other words, if I have 3 front and 2 rear speakers, all of the black wires are connected to each other inside the amplifier. Is this correct?
Yes, the black wires normally connect directly to the ground internally.
The key word is normally. Likewise, typically, more often than not and usually.
There have been some multi-channel amps where “black” is not “common” amonst channels. These amps will usually let you know this by blowing fuses or not playing anything out of one or more channels. A friend of mine had a surround amp that was the latter - he used some shielded twisted pair microphone cable for the rear speakers, thinking he’d have fewer holes to drill. Took him half a day to figure out the goof, but at least nothing was damaged.
Common ground speaker wiring is very uncommon. Has been for quite some time now. In fact, most amps specifically warn against wiring them this way so I would make damn sure before doing it!
The most important thing about speaker wiring is to be CONSISTENT with your black/red wiring scheme. This will ensure that you don’t incur ‘sound cancellation’ problems caused by similar frequencies/intensities being produced by speaker cone motions in opposite directions.
Sounds are created by cone motions causing +/- air pressures. So it is possible to have a ‘plus’ sound cancel a ‘minus’ sound (or at least reduce the overall effect). Sorta like noise cancelling headphones.
I have car audio equipment that specifically mentions not connecting together the “-” wires (not labelled “common” or “ground”). (As for home audio, I’m one of this “vintage” weirdos.)
Here is what you do:
- Read the manual.
- If the manual is not available or not clear, use an ohmmeter (or continuity checker) to see if the commons are connected or not. If they are not connected, don’t hook them up together.