Please take any and all of my suggestions with a handful of salt. I highly recommend buying "Sound Reproduction" by Floyd Toole.
Originally Posted by jlp1021
1) The Left surrounds
reflect Youngho's suggestions... placing the side surrounds just in front of the door puts the speaker at 60 degrees. The rear left surround is also placed on the side wall at 135 degrees.
I would highly recommend experimentation in situ here. I believe that the best all-around compromise would probably be 90 and 150 for the side and rear surrounds, but you should really consider trying it a few different ways, if you can.
2) The Right surrounds
demonstrate bringing the side surround perpendicular to the sweet spot at 90 degrees (just next to the door on the other side). This would actually also be 60 degrees for the second row of seats. I have left the rear surround on the wall at 150 degrees.
I assume that this diagram is simply illustrating four different possibilities for surround placement (60, 90, 135, 150). I think the situation illustrated by the right surrounds will probably represent a better experience for all listeners compared to the left surrounds. Obviously, you would want a symmetric setup.
3) I should have clarified that the speakers I'm looking at are the Genelec HT206B's which have replaced the HT206's. Nonetheless, these are probably not designed specifically for on-wall mounting... I'm not sure. I'm looking at the Genelec's because they are active speakers (amps and speakers engineered to provide the Genelec character without other influence).
Looking at the Genelec website, it does appear as though they do have a "bass roll-off" control that appears to dial down the bass below a hinge frequency of around 250 Hz, so maybe this would work out okay, assuming that you could do some basic measurements.
4) Youngho made an excellent observation: I plan to use Audyssey to handle problems with the room. If I buy the Genelecs to get a neutral sound (as much as possible), I'd better put some acoustic treatment in the room to avoid EQ'ing as much as possible! I've got some additional research to do in this area. I do plan on placing a curtain on the back wall (and even a pair of doors that can close behind the curtain (if advisable).
Keep in mind that Audyssey will be of relatively little help with the cancellation that will occur at around the frequency calculated by 565 divided by twice the distance from the bass driver to the wall. Boosting a null like this will be frustrating for you and your amplifiers. Looking at the data on adjacent boundary effects in Toole's book, I surmise that wall mounting with at least 4 inches of fiberglass behind and around each speaker will probably help reduce this cancellation (you would need significant absorption below 500 Hz).
Really heavy, thick velour curtains draped at 50% of their flat width, with some air space (say, 4-6" behind them) will provide reasonably broad-band absorption, rolling off below 1 kHz. Having an opening in the back can have pluses and minuses. The opening will change the standing wave patterns and act as a partial "absorber," since not all of the reflections off the rear wall will make their way back into the room. Closing off the room may help make your standing waves a little more predictable and possibly contribute to low frequency gain (cabin gain), assuming that the room is relatively "tight" in terms of air movement.
5) I'm planning on placing a subwoofer in the front wall; off-center. The sub is suggested for a larger room up to 4,000 cu. feet (my room will only have about 2,000 cu. feet), but the next model down is only a few hundred dollars cheeper and apparently disappoints (sales talk I'm sure, but buying two of the smaller ones gets a little pricey... I have to check).
Optimizing subwoofer performance can be complicated. You will definitely want to take measurements and experiment here. Just think about your priorities (deepest bass possible? smoothest bass for multiple listeners?) and future upgrade plans (later add more subwoofers and/or processing like parametric equalizer or JBL BassQ?)
6) A note about partitions in the room. I'm planning these simply because I thought they might help. The front wall makes sense to me to hide the speakers and gear.... the back on the other hand, doesn't need to be there at all if you think it shouldn't. This would increase the room length by another 7 feet.
If you're looking to hide the front speakers gear, maybe you could build a partial partition in the center so that you can hang your television and flush-mount the center channel speaker. You might create large panels consisting of wooden frames with an acoustically translucent cloth like Guilford of Maine stretched across them. These could be placed to the sides to hide the left and right speakers, which would be placed directly behind them. Also, you could hide LOTS of absorption back here.
One thing to consider is that you can construct some of the partitions as large panel/diaphragmatic bass traps. I know that some experts like Terry Montlick argue against it, but Toole describes some of the bass trapping that drywall confers. Also, I believe Earl Geddes (www.gedlee.com
) discusses methods of wall construction in his book on home theater, as well as at www.diyaudio.com
(look for a very long thread about multiple subwoofers in the loudspeaker forum).
With regards to a center rear channel speaker, Toole and Holman argue against it, even though Audyssey seems to incorporate it.