Once in a while I see threads concerning the use of two center cahnnels. The usual answer from a few is a problem with comb filtering. They say two speakers with the same information will cancel out certain frequecies and enhance other frequencies causing problems with the sound. This makes absolutely NO sense to me. If the two speakers are close (within a few inches) to each other, I can understand that. Two drivers playing the same frequncies that are closer than the wavelength of the sound will cause comb filtering. But, using two centers would put them far apart (as in one above and one below the screen). Why would this be a problem? If I listen to a mono sinal on my two front mains, I don't get any adverse effects. I hear a single sound at the midpoint between the speakers, no matter what. Why would two centers be any different? I know putting them above and below or left and right would not make a difference. It's still a mono signal. Can someone give me a valid reason why this would be a problem? P.S. I will be posting this question in some other well-known forums for more responses. TIA for your replies.