Michael, there is at least one thread with some basic insights on surround over on John's site (should be up sometime today, finally) -
For now, some basic points - according to Thomas, your baffle extensions (the wall surface you see as a finished install) should be quite stiff, NOT hard-coupled to speaker boxes, and several (like maybe 4-5) woofer diameters in any direction if possible. He's stated that speaker boxes tend to put out enough vibrations that they should be decoupled from the "baffle extensions" known as "soffits", or more correctly as "flush mounts" - Ideal, if you were building a super-anal, million-dollar room, would be concrete pedestals isolated from the rest of the concrete floor, with speakers mounted on them on thin pads (to avoid buzzes) - then these isolated "towers of sound" would be surrounded with a fake (but stiff) wall (the flush mount part) that was even with the front baffle of the speaker, did NOT touch the speaker but with less than 1/4" gap, said gap filled with soft fiberglas or similar, and again with the baffle extension continuing in the same plane as the speaker baffle for at least 4 woofer dimensions in any direction.
The large area of baffle extension keeps the speaker from exhibiting a "horn effect" for the woofer, which can narrow the sweet spot - that in turn can make the surround effect spottier than it otherwise would be.
Another aspect of surround that's different from an RFZ, stereo only room - virtually ALL the surround pioneers I've been aware of (Tom Holman, the "TH" in "THX", Bobby Owsinski, head of Surround Professional, to name a couple) - everyone who's publishing tends to make ANY surface that a speaker points toward ABSORBENT, so that surround speakers don't cause early reflections which cause phase smearing and screw up stereo imaging. Then, to avoid too "dry" a sound, they are "putting back" the ambience with DSP.
One method I've considered along this line to "have your cake and eat it too" is movable absorbers of some kind to be placed on front/side surfaces when mixing in surround. I've drawn one method on John's site that uses beveled "rails" to hang absorbers on when needed -
Another point is time delay - you need either all speakers (except maybe subs) to be equidistant from the mix position, or else there needs to be a sub-millisecond accurate delay on closer ones to compensate. Phasing problems again, especially at higher frequencies where (literally) 1/2" can be heard to cause a change.
For the degree you want to use surround for, other than path length (you didn't mention if it's equal) before you go any further I would enlarge your mounts enough to allow for a little more space around the 2020's, and set them on approximately 1/4" pads, softer than the typical neoprene - I've found that most "mouse pads" are a good consistency for isolation without allowing too much "rocking" of the speaker due to low freq cone excursion.
Then, you need enough space around the other sides of the speaker boxes for some "stuffing", as I mentioned - if you keep the actual opening thru the heavy "baffle extension" so that the gap between speaker and baffle extension is 1/4" or less, that will satisfy the need to eliminate diffraction effects of the lower mids "wrapping around" the edge of the speaker - the "stuffing" between speaker and baffle extension keeps this from being a problem with higher frequency, shorter wavelength sounds. For looks, some thin black or charcoal grey foam evenly pressed in around the speaker would keep things flush without showing any of the yellow fiberglas that's alongside the speaker box.
Ventilation for the amps has been drawn by John somewhere on the site, forget where - bottom and top of the flush mount's venting, basically, with absorption "breaking up" the possible reverberant "organ pipe" effect of an air column.
Don't think I missed too much here, but not finished with my coffee yet - If I raised any other questions, fire away and I'll give it a shot... Steve
The more the better. I mean, don't hold nothin back ya hear?
