big screen - two channel system enough for dialog?

>If I have a large screen (100"+), will I need a dedicated center channel to hear dialog well??

No.

It may even be more intelligible without a center channel where you don't have an acoustically transparent screen which forces center channel placement above or below the screen where it gets a lower midrange boost due to the boundary proximity.

I turned off my mis-matched center channel in my main system and haven't gotten arround to building appropriate center channels for either main or bedroom systems (where it's on higher on my agenda since I sit off-center in bed which produces image shift, although that does not interfere with intelligibility).

>I am concerned about blu-rays needing to downmix from 5 to 2 channels and with such a big screen and separation of my mains, will two channels just make the dialog more diffuse??

Not with good speakers and setup.

FWIW, I'm speaking from experience here. I ran my 100" diagonal setup with mains 4' off the front-wall, 8' between tweeter dome apexes, center channel off. It's not an issue.

I've done this type of thing before. Personally, I find surround sound annoying. If stereo is your main concern, don't compromise your 2 channel system at all. The first thing you need to do is hook up your video source up to your main system and just see how it sounds. You can probably stop there without changing a thing. If not, you may have to get some separate HT components. At that point, it becomes hard to make a recommendation because there are so many different paths you can take to get the results you are looking for. For example, you may go with a receiver and some passive speakers, or a HT preamp and some powered speakers, or some type of combination. Its possible to use your current equipment and get a HT preamp with a pass through option, or don't touch it at all and just work around it. In the end, whatever you do will have to be based on decisions that you make. For me, as long as I can hear it, its good enough for me. I don't need much more than a TV with built in speakers. Most likely, what ever you choose will be somewhere between my basic needs of TV quality audio and your current 2 channel system.

Here's a couple of things you may want to consider. If you end up going with a centre channel, you may not want to buy one. The reason for this is that I find typical centre channel speakers are almost always over powered by the main speakers. You can always buy your way out of the problem by getting more expensive/powerful/bigger etc.. centre channel gear or just get a regular pair of stereo speakers. Put 1 speaker on each side of the screen and get a stereo amp (Or 2 powered speakers). Feed the same centre channel signal to both channels. Doing it that way makes it so much easier on the equipment. Just think how much more you would have to ask of just 1 centre channel to get similar results. Another benefit is the imaging. Its just like listening to a mono recording. You get a rock solid, stable image, that's very clear. The only other thing I would suggest is not to bother with side or rear channels. Its just not necessary. The system should sound fine with out them.If you like surround, that’s another matter. No reason to buy something like that unless you really want it.

thanks for all the responses so far. i pose the question now because I am building this room from the ground up and am trying to figure out how much wire/conduit to lay, the general layout, and of course budget. from what i have read, there are lots of people who think 2 channel is not only better value, but superior in many ways.

i just worry about the separation of my mains when it comes to dialog as I will be using a pretty large screen and I don't want it to be high up. So that leaves mains spread apart which means they'll have to be well out into the room.

one solution i was thinking of was to use Klipschorns (i am one of those high efficiency plus low power tube kinda guys) in the corners. this would allow my big screen in the middle, at almost any height, maybe with a couple of subs underneath, and the horns off into the corner. This would leave the floor clear, a big bonus since I have small kids.

Zd542, I totally take your comment about centers being too small in many cases. the HT systems I have heard often have this problem, and I think quality two channel might even be better in this case as imaging might be better.

I know I can go with the trial and error method, just want to avoid tearing up walls, repainting, etc if I can.

20' diagonal screen seemed to me the size in Lowes theatres for sub-100 people audience:-)