Center channel question?

Does anyone know if there is a practice of limiting the low frequency sent to the center channel from the mixing process? I ask because I see alot of high end center channel speakers that dont go down below 40 cycles, and these are sold in packages with up to 6 matching towers for home theater, so I started to wonder why sell 6 speakers that can dip to 20HZ or below and when it comes to the center make it so "light weight" compared to the others? Is this because material sent to the center typically does not require it? I know it is not because of size because some of these speakers are very large and can be fitted with any driver and cross-over of choice.
Please dont say it is because of the THX 80hz rule because these manufacture's would not be packaging 6 towers with full range performance in the system had that been the case. thanks
Personally I like bass coming from the center , suppose you are playing a 5.1 Audio disc and the singer has a deep voice ? . However most of the newer televisions , Plasma, DLP. LCD, etc have very thin "tops" , therefore it is becomming next to impossible to place any center channel speaker on top of your television.
Chad- I believe that you are correct. Anything below that would be sent to the LFE channel (and the mains if you have selected "large" for speaker size.
Thanks swamp, what I meant to ask is if there is generally
material encoded on the center track that dips into the low cycles......40, 30, or even 20HZ, or is frequencies that low not even put on a DVD center track? Although I am smart enough to know it would be rare, would a scene with a large explosion have 20hz signals in all 3 fronts?
Just because the manufacture sells it, does not mean that it is right. All speakers in your home theater should be the same as your left and right. Center speaker designs have evolved because of the aesthetic idea that they need to be oriented sideways or be physically smaller to look good above or below our TV's. Marketing and sales love this, because now you "need to buy this center channel speaker." It even looks different than anything you have. Oh, and the same goes for these surround speakers. You need some of these too. In the old days, this was true because the old di-poles were supposed to provide a diffused sound field from the Dolby Surround soundtracks. Now we have Dolby Digital 5.1/6.1, dts 5.1/7.1 etc... which requires multiple full range speakers that can image just like your front speakers. Why do manufactures still sell di-poles? For marketing of course.

As far as the mix goes, 50% for the center, 40% for the L&R combined and 10% for the surrounds. So the center channel needs to be equal to the L&R or the best speaker in the system and often it is not. Most horizontal designs have a narrow dispersion characteristic which is not what you want either. The Dolby digital frequency recording spec is 20-20K for all channels. So yes, your 40hz center channel is "light weight" or less than ideal. The sub channel is 3-120hz for special effects.

One thing to keep in mind about home theater vs. 2 channel. The goal in home theater is pretty good sound for the audience (multiple seating locations). In 2 channel we are going for the ultimate image "you are there" experience. Proper speaker choice and set-up can go along way when it comes to home theater. Five or six really good hi-fi speakers and a sub can kick ass on most manufactures "home theater systems."
thanks Steu and Darry
Yes, on a McIntosh preamp you can select for center channel speaker size, small, or large THX.
For a music system the center channel speaker is most important, and should equal or exceed the performance of the others. However, for movies, the center channel is used for dialog, and dialog is more intelegible from a speaker with relatively narrow bandwidth, in particular reduced low bass, which makes male voices "boomy".

I agree with you that the presence and quality of the center channel is more important for music but that's because I (we?) regard music reproduction as more important and critical.

However, I think your description of what's better for movies is incorrect and a bit cynical. I have found that the better the center channel and, more importantly, the better matched it is to the main L/R, the clearer and more intelligible centered speech is (to say nothing about anything else in the center).

In essence, if you get it set up right to do justice with music, the movies will sound great. The reverse is not necessarily true.

Kr4...Optimum voice intelligibility has been extensively researched for applications like air traffic control communications and alarm annunciators, and is achieved with limited bandwidth and shaped frequency response so extreme that no HT theatre speaker could be sold that way. Also, women’s' voices are much better than men’s', probably because of the lack of lower frequencies. Of course, intelligibility and realism are two different things, and so long as you can make out the words a wide range speaker is fine. It's just hard to find a wide range speaker that reproduces the male spoken voice well.
I see what you are saying but do you mean to imply that distinguishing the voice from the background is 'better' than reproducing the voice in correct relationship to the background? (That's what I see in your last sentence, in distinction to what precedes it.) If so, that's a distinction between home theater and PA, not music and home theater.