putting speaker vertical or horizontal?

Horizontally-arrayed drivers which are farther from each other than 1/2 wavelength, based on frequencies which both play (for example, at crossover), will result in a pattern of cancellations and reinforcements in the horizontal plane. This results in varying frequency response as one moves even slightly off dead-center. Besides, both ears cannot be dead center at the same time, anyway.

Kal

Kr4...I understand what you say, but it doesn't always seem to work that way. Suppose you had two drivers spaced 6 feet apart...wouldn't they (ideally) image as one driver between them? Now, put the tweeter at that spot. As a point of interest, just about every speaker designed for center use is of the MTM configuration.

Would they image? Possibly or we would not have stereo, would we? OTOH, that is with slightly different signals. If you compare a mono signal over the pair with a mono signal over a single centered driver, you can hear the difference in terms of image stability with respect to head movement.

As for the ubiquity of MTM centers, that is a model supported by its visual, rather than its sonic, impressions for accomodation to those with the common space constraints. The only good centers have vertically stacked tweeters and mid-ranges. A standard speaker configuration is even better.

Kal

Kr4...I absolutely agree that a physical center speaker is better than the best imaging stereo pair. I use a center speaker identical to the front left/right...a MG 1.6 with a subwoofer. Nevertheless, imaging does work. Some people with HT systems use a pair of center speakers flanking their video screen.

Perhaps also if interest...I am old enough to predate stereo, and I remember state of the art systems back then which used two speakers positioned as we do today for stereo. This eliminated the sensation of listening through a hole in the wall.