No, of course not. You will hear about things not matching, etc., but really no 3 speakers will sound exactly the same in 3 different locations in a room.
I stressed over this for about a year or two until I got a pair of NHT SuperOnes to go with the Zeros I was using. For kicks I put one of the zeros on center duty and listened for a match. No match at all. I switched in and out all 4 of my NHT's and never did the center sound like the mains.
So I got a real NHT center, the VS1.2. It sounded just like the Zero side by side, but on the set it sounded different.
So I said screw it. Got my $200 back, went out and got a cheap BIC 62 CLR. It actually comes closer than any NHT I tried when it's on the tv set. Pure luck I guess, but I'm happy as a clam.
If you can, try to match the tweeter design / material.
If you put two different brands of speakers together they will explode, leaving a gaping hole in space-time.
I've always heard that it is not in your best interests to mix different brands, as the drivers won't match very well. Given that three speakers in a non-perfect space will sound different, it could be claimed that you might as well have three different speakers. I think that in the interests of minimizing that difference, the speakers should be as similar as possible.
If you use a totally different speaker for a center, the home theater police aren't going to give you a ticket, but it might be worth looking into getting a matching center. Of course, listening will always tell you if something sounds good or bad, so stick with your ears!
ColinM, even though no 2 speakers will match exactly, there are certain traits of speakers that will sound similar, call it "character" or whatever you like. Speakers based on similar drivers, design or crossovers will generally match better than those that are not. At the extreme end, put a $10000 pair of mains together with a $100 center speaker, and I'm sure you won't like the sound.
Yeah, I know. That's why I suggest sticking with the same type tweeter. The BIC and NHT's use silk (textile), so they are more likely to sound similar vs. a horn tweeter, etc..
I used to run a sealed 6.5x2 + 1" titanium center, thinking the sealed charachteristics would mate with the sealed NHT's. In fact the tweeter made the bigger difference, since the BIC is a 2x6.5 ported...bass below 100 goes to the sub anyway, and the tweeters sound very similar.
The BIC is ~93db efficient, whereas the NHT's are 86. My trims are all over the place, but the soundfield is fantastic!