Originally Posted by Jim1961f
I've read soooo much conflicting info ("you'll love the sound of the phantom center" / "NEVER use a mismatched center" / "It doesn't matter if it's mismatched as long as it sounds good to your ears", etc.)
Well, everybody has different priorities, as well as sensitivities to various issues.
Phantom centers should sound fine if you're sitting in the sweet spot, but those who are sitting to either side of the center will get some "phasing" in the center channel content, which negatively impacts clarity. While some degree of this is unavoidable in the general case, what an actual center speaker offers is dialogue that virtually always (with some exceptions, as with anything) comes from a single speaker, which helps improve dialogue intelligibility for movies. While this is negated somewhat by the horizontal MTM configuration of most center speakers, they still work significantly better than phantom centers in this regard.
There is also the issue of the soundstage shifting to the side on which one is sitting, with sounds being imaged in the wrong locations/directions relative to the screen--having a center speaker does not eliminate this issue entirely, but it does substantially improve things. Some folks may not be very sensitive to (or even aware of, since they normally sit in the middle) these issues, so they may consider center speakers superfluous, while others find these issues bothersome, and recommend using a center speaker whenever possible.
Originally Posted by Jim1961f
If I do go looking for a mismatched center, is there anything in particular I should be trying to "match"?
The goal is for a center speaker to match the "timbre" and the capabilities of the left & right front speakers. Without going into great detail, "timbre" is basically how a speaker sounds, and it involves more than just frequency response. All three front speakers having the same (or sufficiently similar) timbre allows them to work together more seamlessly, and precisely place sounds across the soundstage and even in front of the speakers, to your perception (known as "imaging"), without calling attention to any particular speaker. Mismatched speakers image poorly, resulting in what some would call a broken soundstage.
As with the issues of phantom centers, perhaps some folks aren't as sensitive to them as others. I suppose that it is also possible that low-end systems could benefit overall from devoting more of their limited budgets to a significantly higher quality, albeit mismatched, center speaker. Such systems may image poorly to begin with, for example, so you wouldn't be losing much while gaining higher quality sound for a very large portion of most movie soundtracks. Then again, it could be argued that it would be better, given a limited budget, to forgo the center speaker entirely so that you could spend more on the left & right fronts (and use a phantom center, of course).
Which option would be the best overall depends on the individual case. Hopefully the overview here gives you some idea of the factors involved, though.