Purpose of using same speakers for surround?


So, I'm wondering why I've heard it is best to have 4 identical speakers for fronts and surrounds? Since the rear (or surround) speakers are only giving out a limited amount of information to fill in details, I see no real reason that any reasonably competent speaker that reproduces down to 80hz wouldn't be just as effective?

In my case, I have been using matched Mirages across the front, with a pair of Pardigms for the rear. I keep thinking about wanting to get another set of Mirages for the rear, but unless there would be some marked improvement, I don't see the point?

Your thoughts would be appreciated.
baxter178
Not all multichannel music limits the surround channels to ambience. I have TACET CDs of chamber music which assign different instruments to different channels. I realized that I needed to upgrade the surround speakers when the viola had more robust sound than the cello.
All five channels are capable of the full 20-20kHz bandwidth, according to Dolby Digital.
IF they all sound similar, it makes it easier to tweak teh rest of the system for optimal performance.

If they dont', it may well sound good or not, just perhaps harder to tweak to get to a desired result.
For space reasons I have in-wall speakers for the rear which work fine. Plus I didn't spend a ton of money and concert DVDs sound pretty good.
Some room correction software will give you a visual of the performance of your individual speakers and their locations. Some programs will match to the weakest speaker. Given some work in their placement a matched set will need much less correction if any.

It's difficult to appreciate the potential of your system until you can compare it to being properly setup. As digital film production improves and with Blueray audio looms on the horizon the quality of your multi channel will become more important.