Originally posted by gonk:
I haven't done much with this sort of thing, although I've done enough acoustical calculations to know that it's in many ways more dark art than science. Your comment about the link to RAF's site reminded me of an old 6-part (edit: OK, 5-part plus photo gallery and addendum...) article on dvdfile.com that you might enjoy: Mr. Blandings Builds His Dream Theater . It gets into a lot of the room design and construction stuff that you are asking about.
Is your 5 speaker setup similar to this? And where would you position the 6th and 7th speakers?:
3.4 Surround placement for DVD-Audio listening
The multichannel music programs on DVD-Audio discs are mixed under different circumstances from movie soundtracks. Films are mixed in large rooms called dubbing theaters that are sized and configured like actual cinemas, while DVD-Audio music programs are typically mixed in much smaller recording studios.
As shown in Figure 13, dubbing theaters (and cinemas) use multiple surround speakers arranged along the sides and rear, mounted high to create a diffuse, enveloping surround soundfield. The advice we've given so far for placing surround speakers is aimed at duplicating this effect at home. In most DVD-Audio mixing facilities, however, there are five identical speakers arranged at ear level in a circle around the mixer.
Figure13
Figure 13: Film soundtracks and DVD-Audio music programs are mixed under different conditions.
Chances are that you will be pleased by the sound of multichannel DVD-Audio programs with your surround speakers optimally placed for movie playback. However, if you wish to more closely replicate what mixers hear when preparing music for DVD-Audio releases, you have two choices. One is to effect a compromise by lowering your surround speakers to a height of four or five feet from the floor to split the difference between the diffuseness desired for film sound and the more direct radiation preferred for surround sound music.
The other alternative is to install and switch between two pairs of surround speakers, one optimized for film playback, and the other, identical to the front speakers, placed at ear level for optimum DVD-Audio playback. This purist (and potentially costly) approach is facilitated on some A/V receiver models by the inclusion of connections and switching for two pairs of surround speakers. However, while this approach may optimize the effect for a listener in the center "sweet spot," those seated off-center may hear too much of one surround speaker or the other.
(I am unable to paste photo, here is a link, and scroll down to fig. 13
http://www.dolby.com/ht/Guide.HomeTheater.0110.html#s3.1 DMC