Nice thread for the most part, folks.
My thoughts are that these response models are conceptual. There are many areas of acoustics where we can't actually achieve the ideal, so we do what we are willing to do to get as close as we can. For example, I don't have an AT screen and I don't want one. Therefore my room will be inherently unbalanced - there is little I can do acoustically with a huge portion of my front wall.
When I approached acoustics in my theatre, I made a list of sound characteristics I was looking for and am using that as most of the guide for how I design the acoustics. For example:
(a)I have one main seat, down the middle, that I want to be as good as reasonable for two-channel music. I'm willing to compromise my ultimate multichannel performance for this goal to some extent... at a mix of perhaps 60% multichannel and 40% music.
(b)I want the bass to be even between all the seats
(c)I want the the response to be flat, or possibly with a slight house curve, in all the seats.
(d)I want good dialogue intelligibility from the center channel speaker in all seats
(e)I want the surrounds to sound somewhat "ambient" in all the seats (actually I'm not sure this was on my list but it probably should have been)
I also have some constraints:
(f) I don't want to use more than 2 inches of space on the sides... it is only a 10' wide room. I know this may limit the ultimate quality... that's my choice.
(g) I have some seats close to boundaries. I know that's said to be a good thing, and it might require me to use more absorption than otherwise. Oh well.
(h) I already owned decent smallish speakers which have the typical "normal" dispersion pattern. No horns, no waveguides, no CBT, no d'Appolito action.
And some preferences:
(h) I think I tend to desire a more "accurate" than "spacious" or as it's been put here "pleasing" sound.
(j) I'd like the room to sound larger than it really is.
Note that these aren't complete as I don't have my original notes on hand here - this is just meant as some ideas on one way to proceed.
From there it's simply a matter of figuring out how to accomplish as many of those things as possible, possibly with an order of precedence. for example my biggest priorities probably are:
1) maximum CC dialog intelligibility
2) flat-ish bass response, even in all seats (sort of the same thing anyway...)
3) good (pinpoint) imaging from the front two channels, I think it's useful for both movies and music
The first is going to imply controlled decay time and probably early reflection control. Ideally I'll become able to directly measure this using Speech Transmissibility Index (STI), which is normally considered to be a large space metric but I still think would be fun to play with. I suggested John put this in REW and he said it's on his list but not near the top. He said it's not appropriate for a small space but on the other hand Terry Montlick stated on AVS that he used to use it as part of his alpha certification for home theatres.
The second is going to imply modal control, which I can verify with waterfalls and the various decay measures in REW.
The third is likely to imply control of early reflections from L/R, especially given my speakers - and across a range of seats which does require a fairly broad swath of absorbent in the room - with an end result much like the "thin absorbent almost all the way around" that's been discussed here. Either way it is verifiable with the ETC as has been discussed.
Therefore those three items have been at the top of my acoustical list and the focus of my initial acoustical efforts. Next I'm launching into modal control of the bottom octave, adding subs to even out LF through the room, as well as adding diffusion. An image of my plan is actually on here in the "DIY diffusors" thread and I've sort of come into a "dead height-live height" plan. Will it work well? I think so but who knows... gotta install, listen, measure. I'll measure performance based not only on objective acoustical measurements but how often I say "wow" when I listen to music or watch movies. And by how many times I have to pause and go back to figure out what a character said! (that one better ultimately be never
I should add that a treasure trove of acoustical information is in the GS sticky Acoustics/Treatment Reference Guide
Possibly even more useful would be standards for multichannel mixing rooms. Doesn't it make sense that we would want to hear our media reproduced the way it was intended, and if our rooms sound a bit like the dubbing stages and mixing rooms where it's created then we would presumably achieve that. Plenty of standards are available free online, and avare links to them all in this post
as well as the following one.
I personally think the ideal response model is not the same for all channels in a multichannel setup . As noted before it's not really achievable but my best guess would be Center-NE/anechoic, Left/Right-RFZ, surrounds-ambechoic. As for LF, go for Welti/Devantier/Geddes - which really amounts to ... oh goodness... just make it work.
If you play with the demo of RPG Room Optimizer, it tells you to put absorption at LCR first order reflection points, and diffusers at surround first order reflection points.
I don't claim to be any sort of expert. I have not even yet read Toole's book, the mentioned passages of SSE (though I have read the small acoustical space chapter), or made it through a complete review of the standards in the avare posts above. I look forward to a full review of the Mellor/Hedbeck white paper mentioned earlier which on skimming looked to have some great ideas. And unlike those that Penn mentioned, I actually LIKE to study! It's great to have threads like these around, in fact I'd like to see some further and more in-depth discussion of the ideas. But we also have to face the fact that 99.9% of people on AVS are not at all interested in this depth.