Suppose, many years ago, I had a couple of bare-ended electrical cords embedded in the walls of my TV room specifically for the purpose of powering rear speakers for a prospective home theater. Now suppose that said cords are plain black without any labeling or other indication of “polarity” as represented by the black (negative) and red (positive) jacks on the receiver and speakers.
Therefore, when I connect the rear speakers under such conditions, I’m only guessing, assuming that wrong connections will be obvious when I listen to the output.
So imagine my pleasant surprise, as I resurrected a neglected home theater this past week, when not only did I guess the easily discernible left and right channels on the first try, but I also apparently nailed the red and black jacks because the output sounded just fine.
Suspicious of such good fortune, I switched the black and red wires on one speaker to see what would happen, and it sounded exactly the same. Likewise for the other speaker.
My question is this: What the heck is going on here?
What happens when you wire them incorrectly (black positive on one speaker and negative on the other) is that they become out of phase. Thes means the sound waves produced are not in synch and the bottom end tends to cancel itself out. You often lose the center sound image as well. The results are variable though and depend on the sound source and your listening position.
This site has a speaker test that allows you to test left, right and phasing.
Since it’s only the rear speakers the OP is unsure of, though, I’m not really that surprised that the difference isn’t noticeable. I don’t think they have much bass.
It’s also pretty easy to test the wires, and then mark them with a piece of colored electrical tape at each end, so you know which is which. A simple continuity test with any kind of a voltmeter, or even a light bulb & an extension cord.
And are you sure they are unmarked? Many plain flat pair cords actually have a raised ridge or stripe on one of the conductors to mark them. You might have to look closely, or even feel the cable to notice this.
To elaborate a bit on the physical meaning of this:
If you put a signal on two speakers, but with reversed polarity on one of the speakers, you’ll have a situation where whenever one speaker is moving out from its rest position, the other is moving in. If you think of your speakers as pistons, pressurizing and depressurizing your listening room, an out of phase hookup will always result in zero net change in the pressure of the room, no matter what the signal (for monaural signals). OTOH, speakers hooked up properly maximize the pressure differences imposed on the rooms’ atmosphere.
In a big enough room it can be hard to tell the difference between the two hookups, especially with stereo sound, but you might notice some dead spots when playing a monaural source.
Some people do this on purpose to hear things that are normally buried in the mix. The idea, as I understand it, is that when speakers are out of phase, stuff that’s in both channels tends to get canceled out, allowing you to better hear the rest. Here’s an explanation:
Please note that polarity does not equal phase. Phase is about the time relationship between 2 waves, whether light, sound or otherwise. Polarity is about electrical positive and negative.
As others have said, hooking 2 speakers up out of polarity will mean a loss of low end and a loss of imaging. You can reverse this by flipping the wires on one side. As for how to test it, a multimeter would work, or with the wires connected to the speakers and disconnected from the amp, and the grills off the speakers, touch the wires to the terminals on a 9-volt battery. The cone will move either in or out depending on how it is wired. Note which wire was hooked up to the negative terminal on the battery and mark it somehow, a piece of tape, a sharpie, something. Do the same for the other speaker and switch the wires so that the speakers move the same direction if needed. Now reconnect the speakers to the amp, putting the marked wires on the black or - terminals and the un-marked wires on the red terminals. Now your speakers are hooked up in the correct polarity.
To adjust phase, move one speaker forward or back, keeping in mind that this move will only affect a small range of frequencies, and, more likely than not, negatively.
By golly, you’re both right! When I looked at those cords again in broad daylight, I noticed not only very fine ridges on one side, but also very small, faint white lettering on the other. Both of these features were obscured by white paint, drywall dust and the dimly lit room when I first made the connections.
Of course now I won’t rest until I again subject my body to the contortions required to ascertain the connections behind the wall unit, a mission only slightly complicated by the six feet of regular speaker wire I had to splice in to reach the receiver. I have a feeling I’m about to enter the desperate head-scratching depths of polarity hell.
In any case, thank you all for the assistance and education.
the reason they sounded the same is because speakers are essential electrical plungers. You apply current to the (voice) coil and the cone moves forward. In your case the cone moved backward. Speaker cones are suspended so the voice coil can float back and forth over the magnet in both directions. The vibration of the cone moving back and forth is essentially the same regardless of which direction the current is applied. There are speakers that don’t use voice coils but that is the general nature of most of them.
This becomes a problem if it’s an isobaric set up with one speaker driving directly behind another. They would fight each other in this instance.