Patrick Stewarts voice-over at the beginning of X-Men will help with smoothness and clarity, and I guess the Matrix has a pretty busy centre channel if you wanna check it under 'stress'
Well, the center speaker carries ALL the dialog of a movie, and the special effects and the music/soundtrack.
This is a difficult task for any single speaker to do well.
So I would advise you to find chapters of movies that have male/female voices, special effects and music.
When I searched for the best center speaker, I would disconnect the L/R and rears so I could focus on just the center.
I became very familar with some chapters of DVD's and took them to every audition.
These were:
Star Trek:First Contact - Ch 2 This is the Borg Battle scene at the beginning. In about 7 minutes it has nearly every kind of sound you can imagine.
Air Force One - Ch?? The chapter where they hijack the plane. Has lots of special effects & sounds.
When I tested, I tried several things:
- Closing my eyes and turning around several times. Then try to locate the speaker by sound alone. (I wanted to avoid speakers that acted like a point-source of sound).
- Listening to the speaker while sitting on the floor, sitting in a chair, standing and moving off-axis. (For my family, having a narrow sweet-spot is a bad thing).
Note: Many speakers sound good with movies, but Music will often uncover flaws in a speaker that are ignored with a movie soundtrack. For this reason, you should bring a favorite music DVD with you to the audition.
An ordinary CD can be used, but these are NOT designed to send music to a center-speaker. So you are relying on the receiver/processor to route some sounds. So if a otherwise good center sounds funny with a CD, is it really the speaker, or the electronics doing something funny? You cannot tell. So bring a music DVD with you as well.
Note: In my price range, two center speakers stood out:
Definitive Technology CLR 2002 (I bought based on this center)
Energy AC-300 (This was a close second)
Hope this helps.