Two mono center TV speakers out of phase?


I would like to use two mono center speakers with one over, and one under the TV to make the sound image appear to come from the TV, not above or below it. My home theater dealer said that he has talked to experts on the subject who told him not to do that because the sound will be out of phase. To me that makes no sense at all, because the mono signal to both speakers is the same, the two speakers are the same, and the two amps are the same. I would much rather hear the sound coming from the center of the TV, but what would cause the sound to be out of phase, or what other problem would this setup cause? This mono center channel is created from the left and right signals and is not a separate third center channel.
redwoodgarden
I don't understand this either. I am not a HT man, I have one but it is a stereo one, but how can 2 mono speakers be out of phase with each other? I don't understand how they can be out of phase with the stereo signal either but as I said I am not a HT expert. Three channel sound was current in the early 60s when I got into audio and I had a Fisher amp that had a separate mono output for a 3rd channel. It worked fine then and a modified version should work now.
Just guessing, but maybe he is referring to phase differences of reflections off of the wall behind the tv set. The path length from one center speaker (say the top one) to that wall and back to that speaker is different than the path length from the the bottom center speaker to that wall and then to the top center speaker. Perhaps that could result in some degree of frequency response irregularity.

Regards,
-- Al
Just guessing, but maybe he is referring to phase differences of reflections off of the wall behind the tv set. The path length from one center speaker (say the top one) to that wall and back to that speaker is different than the path length from the bottom center speaker to that wall and then to the top center speaker. Perhaps that could result in some degree of frequency response irregularity.

Regards,
-- Al
Haven't heard the out of phase comment, but have heard 2 closely spaced speakers playing the same signal can have comb filtering effects (destructive interference affecting frequency response=peaks & nulls) Think your speakers are far enough apart that the effect would be minimal. I use 2 center channel speakers on either side of a 100" diag. screen, helps balance apparent "image size" between stereo front L & R and the center channel.
If the speakers are different distances to your listening position, the sound waves from the two speakers will arrive at different times and can cancel each other out, or amplify each other, at the various different frequencies. I suspect that is what was meant. Even moving your head a few inches can cause this with the higher frequencies.

I don't think that putting mono speakers above and below the TV will make it sound like the sound is coming from the TV. The sound will still come from the speakers above and below the TV. That's what mono is and does. You need stereo, not mono, to do what you want to do.
Good thoughts in the preceding posts, except that I would respectfully disagree with this statement:

I don't think that putting mono speakers above and below the TV will make it sound like the sound is coming from the TV. The sound will still come from the speakers above and below the TV. That's what mono is and does. You need stereo, not mono, to do what you want to do.

There is no difference between a pair of stereo signals with identical left and right content (or in this case, top and bottom), and a mono signal fed to two identically placed speakers. You can easily verify that by playing a mono recording through your system; the result will be a focused image centered between the speakers, assuming the speakers and amplifier are connected in phase, and that there are no significant channel imbalances.

Although in BOTH cases I believe that Hhiggins is correct that if the speakers are too close together, comb filtering effects can occur at frequencies which are high enough to make the effects audibly significant.

Regards,
-- Al
I had an extra speaker when setting up my system. I tried one for the center and two next to each other. The pair sounded much better. I laid them down with the tops facing each other. Ran a Y splitter to 2 channel amp to run the speakers. It worked great for many years.

If you put one speaker up high and one down low, you will get the signals at different times which could muddy up the sound?
"There is no difference between a pair of stereo signals with identical left and right content (or in this case, top and bottom), and a mono signal fed to two identically placed speakers."

This is correct. A stereo signal with identical content left and right is, essentially, a mono signal. And of course, you should get a centre image if everything is set up properly as you would with a stereo pair. Therefore, upon reflection of my earlier comment, I would say that Almarg is correct about the imaging issue. However, proper distancing so that the two mono signals are not interfering with one another remains an issue to watch (or rather, listen) for.
Just do it!
Thanks for your comments. I still don't see why two mono speakers equal distant to the sweet spot using two identical amps will cause a problem. I'm using a 52 inch TV screen so I don't think that distance between the speakers should play a role. Perhaps connecting the two speakers to the same amp in series may have this negative effect, but I'm just guessing. I wouldn't do that anyway. I'll take Cyclonicman's suggestion and just do it.