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.
I don't use matching rears. When I've tried it heard no difference. You are right, as long as the sound effects channels are competent, good enough for me.

I suppose if you want a visual match, that's OK.

Perhaps those with a really high end system, and listen to a lot of multichannel music would be better off matching. For the rest of us...
Not one manufacturer has yet to produce a completely neutral speaker. Not only do different designer/manufactures deviate from neutrality differently, but even models from the same manufacturer deviate differently from each other. With that said; it is more likely that a given designer/manufacturer will more likely have more consistent design priorities, and even perhaps shared components within a given line, and therefore greater sound similarities. There is good reason to match sounds as closely as possible. Different variances from neutrality can add quite a bit of distraction from the semblance of reality. While perhaps not as important as matching left and right channels, the same reasoning for doing so, holds true for matching front and rear channels.
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.
It is an interesting theory, but a very bad way to allocate your budget. Lets say you have $20K to spend on those four speakers. Your options are spending $5K on four identical speakers. Alternatively you can spend say $9K a piece for mains and $1K a piece for surrounds (or $8K/$2K - whatever) . If like most of us you spend most of your time listening to either stereo, movie soundtracks with most information on the center channel and the occasional discrete MCH misc source with lots of information on the surrounds, you are far better off spending a lot more on mains.
Edorr, your dismissal of the previous advice and subsequently offered advice, is predicated on assumptions and qualifications that have not been provided by the OP. Even if what you suggested were true for the OP, very often the budget allocation could permit the less expensive surrounds to come from the same manufacturer, which would more often than not, be a better match with the mains.
The question is about 4 identical speakers (not same manufacturer). I totally agree that getting the same manufacturers speakers is typically a good idea. But I stick by my opinion that in most applications getting 4 identical speakers is not. (Exception would be an avid classical music listener with extensive MCH SACD collection).
Edorr, I suggest you read past the title of OP opening thread opening. The other obvious exception is for those that have separate audio and HT rooms.
Interesting thoughts all, and perhaps my topic was a tad too broad?

I can now see a definite merit for same speakers if I were listening to classical music via MCH SACD... I am not. Clearly this would be ideal for those that do.

For me, I listen to various forms of music including rock, modern jazz, pop, and r&b among others, which I run through 2 channel via an AH! cd player.

I also like concert videos, and movies in 5.1, via DTV(HD), or a Panny Bluray.

My modest system includes a Rotel 1077, NAD T175, Mirage M7si - MC2 - PS10, and early Paradigm's for the rear.

I'm not talking about a major investment in picking up another set of M7sis, but for those of us with similar listening habits, do you feel the change would make a significant improvement, or not worth the effort?

IMO, for not making a major investment, I feel the change would be a significant improvement and worth the effort.
Purpose of using same speakers for surround? TIMBRE.
I just saw Mission Improbable at an Imax theater. While I couldn't tell exactly what speakers they were using for the rears they were very large PA looking. I don't go in much for today's shoot-em-ups but the previous MI's were at least somewhat believable, well subjectively anyway.

The sound track had some moments were the rears were at a very high volume with almost nothing coming from the front. Seldom used, the effect was very dynamic. Numbed by the shear excessive use of what's become one note explosion low frequency the audience was clearly startled by this massive discrete jolt from the rears.

Is this an indication that film audio is beginning to get over the ridiculous? Maybe not.

In my previous 5.1 system using "surround" speakers the effect was novel compared to my current 7.1 using matched speakers. As a reminder, 7.1 is not about room size. It works very well in a small room.

If your combining two channel and HT you need to bias the quality of one or the other. IMO two channel is simply too delicate. That said, matched speakers are worth it.

OK... so I'm using M7's up front. I can pick up another set of M7's for the rear. Per your recommendations, this solves my 5.1 dilemma, but there is no way I'd be adding a 3rd set for 7.1 LOL! It's a good size room, but not THAT big, and the wifey would probably pull the trigger if I tried having 6 of those towers in my bedroom!!! Guess I'll be with 5.1 for quite a while, but that's my mo anyway. The closest I ever get to new is new old stock :)
BTW, is there even 7.1 material out now?
I still think it's best to have all identical speakers, but if you have to have the rear different from the front, the rear should be a bit more laid back and less bass output vs the front so the rears won't call attention to themselves.
Baxter, is there a small version of your M7's with similar drivers? I think if you pole people using matching speakers they're usually small bookshelf sized speakers with a subwoofer.

Matching floor standing speakers might be overkill and difficult to locate within your room compared to wall mountable speakers.

Titles using 7.1 is small but growing. Most modern 7.1 receivers have the ability to matrix 5.1 into 7.1 with very good results creating a more discrete surround effect in most any size room. You won't find many 7.1 users going back to 5.1

I'll do a little research and try to find out what the bookshelf size speakers from that family were. Obviously the speakers are older and harder to find, but that can work out in a huge price discount too (small budget).

That (using M series bookshelf speakers) was my original plan, but one keeps reading about same speakers all around for best sound (yes that's hard with towers), hence my post.

I honestly love what I have, since moving a Proceed amp3 to a stereo setup and adding a Rotel 1077, the Mirages came alive, not in an obnoxious brighter way, just much more detailed and open which I didn't expect with the amp3 being a nice piece to start with. Then replacing an old Yamaha receiver (used as a pre) with an NAD T175, and holy &^(-... I've seen the light of day!

One thing I have learned from the knowledge of the people on this site, is that it isn't the name on the pieces, but how the pieces you have work together. After years of wanting and waiting, I'm pretty damned happy right now :)

Now, if I can tweak it up just a bit more for minimal cost, by matching the rears, and possibly going to 7.1 I'll be good for a while.
If there are any members that would share with me the appropriate model #'s in the "M" series I should be looking for, it would be helpful :)
So I emailed Mirage and got this for a reply:

"The original and former Mirage M Series models would have been engineered and designed from the former Canadian based Audio Products International (API) group which ceased to exist in or around 2006. Klipsch Group, Inc. USA acquired Energy, Mirage, Athena brands including all remaining replacement parts and limited product data for some of the older models (I have included some of the older PDF copies of any information I could still find for the older M7si and MC-2 models. There is no specific manual available for the former MC-2)."
"I am very sorry we would not be able to make any further recommendations to accommodate the expansion of your system using these older model speakers."

They say they can not offer any recommendations for the older speakers... I know there are members that claim to have sold Mirage in the past, perhaps one of you could help me out with model #'s that would timbre match my fronts?

There's lots to consider for balancing things out to maximize the "team effort", which is a system. The more you do RIGHT, the better chances you have of attaining a quality effort, and great results.
Sure, you can get buy, and probabaly be just fine doing mix match. And, yes, the rears arent' as critical to the peformance of the system, as what's happening up front...you absolutely MUST match the front 3 speakers to produce a believeable, coherent soundstage with unifor tonality there. And this is the bulk of your pressentation.
Heck, I use two speakers, and sometimes not even a sub to watch on my big screen/receiver setup these days. But then I'm a bit lazy with all of this right now, and don't really care so much. I know..sad isn't it.
Still, if you want to add another properly balanced ingreadient to your mix, and keep the quality level of the system up, and be ambitious about it, you really should get the matching speakers ALL AROUND in the system, to maintain coherence and integrity, and so your soundstage has the potential to be transparant, and so you can just dissapear into the sound, and the gear gets out of the way of the playback chain.
What often happens is people end up listening to a collection of "gear", with limited fidelity potential and realism to the perforance of the audio. It can just end up being sound coming from different directions...and not really great sound, at that.
Think of it as taking the time to carefully spice a dish your cooking. Yes, you can be happy with just "ball parking" it. But heck, why not just throw anything in there, if better quality can't be had matching everything in the first place? Cause you're just not gunna end up with anything SPECIAL from the sytem, otherwise. Nothign you can't get from a better home theater in a box effort, if you just throw it together, really.
Just some thoughts

Considering that I am extremely happy with my front 3 speakers (and how they perform with my other equipment), I don't believe I would be throwing some "gear" together by going with bookshelf speakers for the rear, so long as they have the same drivers as the fronts. This would give me a timbre match, or am I wrong here?

If I am incorrect in this understanding, please let me know. I do not profess to being up to date or overly indulged in electronics... that's why I come here to ask you guys that are more involved.

Also remembering that on 12-17 I posted this comment:

"I can now see a definite merit for same speakers if I were listening to classical music via MCH SACD... I am not. Clearly this would be ideal for those that do."

Thus, I believe the bookshelf speakers from the "M" series with the same drivers would achieve my goal. If I am incorrect in my assumption here guys, again, please let me know!

So, unless I get responses informing me I am wrong, and need the larger M7si for the rear (considering my use), what I really need is someone that knows the Mirage "M" series well enough to recommend a suitable bookshelf speaker from that series, so I can begin my search.

Thus, I believe the bookshelf speakers from the "M" series with the same drivers would achieve my goal. If I am incorrect in my assumption here guys, again, please let me know!

I think everything in the ballpark of approximately 80-20kHz should sound as similar as possible, with a sub carrying the bass below that.

It would be nice to out if they did have a full surround system with your speakers used. I searched the web, and can't seem to find any system reviewed with your speakers used for the front. I'm guessing there are smaller speakers made by them that would sound similar, or "house sound."

The new owner should provide this info IMO.