Speaker on its side as a center?

You might check with B&W to see if there is any concern from their end. If the speakers have any ferrofluid cooling that may prompt you to rotate the drivers. I had a freind that did it with his old Kappa &'s and the Emit tweeter failed about 3 mos. later. Upon reading the manual Infinity instructed the user to rotate the tweeter when laying the cabinet on it's side. Just a thought.

Not a good idea. You'll be relying on the speaker's "vertical" dispersion, which is usually much worse than its horizontal dispersion. Of course, most people use horizontal center speakers, which suffer from the same problem. The best center speaker is another of the front speakers, mounted vertically just like the others.

In my view, all center speakers are compromized by their position above or below the TV. However, most of the material played by the center is dialogue with some special effects. The best position is to get it as close as possible to the height of the mains with the tweeters at the same level. Being on its side is less important than any other factor. Good luck!

I use 6 identical speakers for my 6.1 system. I was laying the center on its side for esthetic purposes, but tried standing it up to hear the difference. There definitely was one. Tweeter dispersion patterns and all, I believe.

Only way to know is to try it out and see what works for you, your room and your speakers. I would certainly give it time in any position to see what you think. It's not really an A-B in 5 minutes type of test IMHO.

Enjoy,
Bob

its geerally for dialogue.....no big deal