@goin3wide – I noticed a similar thread on another forum, posted by a Jooobs. If that’s you, you’ve already read it. If it isn’t, you should
have a look at it.
That forum does have more readers and posts. Sometimes that’s a good thing, and sometimes bad. Many posts there agree with the posts here advising you against using two center speakers. In this case, I think the abundance of differing opinions on that forum is clouding the issue. Too many have posted about the difference in impedance between one or two speakers. That’s an electrical problem that may or may not have an impact on your AVR or amp. It is unrelated to the real issue of comb filtering. That’s an acoustic problem, what can happen to sound once it leaves the speaker.
In particular, one poster, dfa973, is mucking things up in several ways. First of all, he tries to dominate others by talking longer and louder. Second, he seems to confuse the commonly used two mid-woofers in sideways MTM speakers with the very different question of two widely separated center channel speakers. And third, he thinks theaters and homes have the same acoustic problems. His idea that “if it works in a theater, then it must be good at home” is wrong. The distance sound travels must be understood in terms of wavelengths and not feet or meters.
His set up has a TV set (of unknown size) with center speakers above and below. Yours has a larger projection screen where you want to do something similar. That poster is confusing his set up with yours – the distance between those two pairs of center speakers will be quite different. And yes, with sound waves, that distance does matter a lot. Comb filtering problem becomes hard to describe without considering the distances between both speakers and the listener,
AND the wavelengths of the sound. At 500 Hz the wavelength is about 2¼ feet, at 1000 Hz about 1.1 feet, 2000 Hz iabout 0.56 feet, etc. The interference of two or more sources of sound varies greatly depending on those distances and those wavelengths. If sound from the top and bottom center speakers arrive at your ears in-phase with each other, they will add together, sounding louder. But if you slump in your sofa lowering your head by a few inches, sounds can easily arrive out-of-phase with each other and cancel. The difference between in-phase and out-of-phase waves is half the wavelength, so yes, it's really a matter of inches. This problem also exists if other listeners are not the same height as you are. It varies greatly with wavelength, and that’s why you see the comb-like teeth on a chart plotting frequency vs. loudness. It's easier to avoid this problem by using a single center speaker. Why would you go out of your way to create this potential trouble?
OK, enough about that. You would do well to ignore dfa973.
You seem to be determined to try using two center speakers, one above, and one below your screen, despite some solid advice from others why you should avoid doing that. Fine, if that’s what you intend to do, go ahead. However, you would not be going about this fairly unless you also compare your two center speaker arrangement to the sound you get from one better quality center speaker. Without that, you can’t compare things, you can’t know which one actually sounds better, and you can't know what you might prefer.
