Help with rear surround speaker options/placement (2 Viewers)

[John E F]

I recently bought an Onkyo 898 and am running NHT SB-1's all around for 5.1 with a Paradigm PS1000 sub. I want to add the two rear surrounds but the couch is against the rear wall. Adding two more of the NHTs won't work as there is a window behind us and they would be far too big. There is room above the window for relatively small speakers. I am wondering if it would be beneficial or I am out of luck due to the seating position? Are they any small speakers that might work, angled form the ceiling perhaps?

 

[Harold_C]

I have the same kind of room setup with both the couch and the surround speakers against the rear wall.
I don't believe that adding center back surround speaker(s) will be a significant improvement with that room arrangement and it is possible that it will actually hurt your surround sound performance.
Here's how you can judge the effect it will have:
Play a Dolby Surround stereo source decoded with Dolby Pro Logic -- either from a VHS tape or from the Dolby Surround 2.0 channel soundtrack on a DVD. Now, switch your center channel setting from ON to NONE, basically going from a derived center channel signal to a phantom center channel. Notice how the sound image "collapses" to the center speaker when it is active and is much more "diffuse" with the phantom center channel? This is pretty much exactly what you can expect at the rear of the room when you go from two surrounds to a derived center back channel. On Dolby Digital recordings, the mechanism for extracting the center back channel signal is essentially a Pro Logic decoder working on the surround channels and the extra speakers become essentially a center channel for your surround speakers.
The extrra center channel localization is definitely what you want in the front of the room because you want the dialog to be strongly locked to the TV screen. However, in the back of the room, particularly when you are sitting close to the speakers, I'm not sure that you want the strong localization on center back channel speaker(s). The more diffuse surround effect from your current two surround speakers and a "phantom" center back channel may well be preferable on the vast majority of surround material. It will certainly be preferable on ambient surround effects where you really don't want to localize a particular sound.
It is my guess that center back speaker(s) will be most desireable in large rooms where the surrounds are essentially at your sides and the center back speakers are some considerable distance behind you. Even then, there are people who really object to the way the Dolby Surround EX decoders collapse the soundfield and prefer the way some alternate 7.1 channel decoders distribute the surround effects more evenly.
If you go from your current optimum set-up with five identical speakers to a system that adds two significantly smaller and different center back speakers located directly above the couch, I think you run a reasonable risk that the system won't sound as good. Before popping for additional money, I would see if the store won't loan you a pair of speakers to play with on one evening or over a weekend. Run some speaker wire across the room and get a ladder or some other way of temporarily putting a speaker up there and see whether you like it better or not.
I could be wrong. You might love it. But remember this: just because the consumer electronics industry feels an overwhelming need to sell you a NEW feature (i.e. taller tailfins or more chrome) every year, doesn't necessarily mean that you must have, or will even benefit from, that new feature. Make sure that you are buying a benefit, not just a feature.

 

[John E F]

You are probably right. The room isn't that big and I certainly don't want diminish the soundfield at all. I bought the Onkyo 898 for other reasons than DD-EX/DTS-ES capability. A new house with a bigger room will have to be the next upgrade. This one will actually be easy to talk the wife into