Just wanted to post the results of a long and ongoing process of tuning my room, just so that folks who have small, non-optimal rooms like mine will have hope that they can get really good results. My room is lke 16' long, about 11' wide the ceilings are only about 7' 8". So it's pretty worst case.
Here is the latest measurements I did tonight. This is from 40Hz to 300Hz:
I've drawn a line down it about -10dB. Except for my one remaining, PITA, cancellation around 65Hz, everything is pretty much within about 1.5dB of that line. I could actually set up a Phase Linear EQ preset that would knock down those two small peaks and that would make it flat to within about 1dB other than the one cancellation issue.
I'm not sure what results other folks are getting, but as I understand it, that's pretty dang good. The remaining cancellation, I just don't think I'm going to be able to get rid of. There's no more space for broadband traps. I guess perhaps a tuned trap at the cancellation frequency is a possibility, but they are pretty costly and if it did really nothing for me, I'd be seriously PO'd, and there's not really any good place to put one if I had one, given the room size limitations. The part of it that's down more than 3dB from that line is probably only about 5Hz across, so it would only really affect a few notes badly, but I can hear it of course if a prominent bass line runs down through it the right way.
But, I guess I can live with it. It's still probably overall way better than many more expensive rooms.
It required a pretty bodacious amount of trappage. Just for reference, in case anyone reading this later wants some estimate, I've got:
1. A raw box of 703 on its side on the floor behind the speakers, so that's 12" thick.
2. On top of that, standing up on end, are two sets of 4" ones with a couple raw sheets behind that, so 10"s coming up behind the speakers.
3. A 6" trap on the wall/ceilng corner behind the speakers.
4. There are two 6" traps side by side (so 4x4') as a cloud overhead, but then 5 raw sheets slipped down the middle between them, so 16" down the middle line overhead.
5. In the left/right corners are two raw sheets thick with 4" bagged traps over those, so 8" from floor to ceiling.
6. On the left/right wall/ceiling corners are 6" traps with antoher raw sheet behind them, so 8" there, plus some 703 scraps thrown up in there.
7. On the wall/floor corner to either side are 6" and 4" traps, so 10" each there.
8. And there's a 6" on the wall ceiling corner in the back.
9. 4" ones on the two side walls for the first reflection point.
I don't have rear wall/wall corners that can reflect back to the listening position, so nothing to do there. Note that, other than #8, there's no treatment on the rear wall. It's a big sliding glass door with curtains and blinds, so it would be hard to treat. I could put a couple back there on stands I guess, but they'd be pretty intrusive. And I've stacked up beaucoup trappage back there and it's had no really measurable effect, so I've concentrated it elsewhere anyway.
That's a lot of 703 for such a small space. And huge amount of time spent rearranging them and moving the desk around and trying monitor orientions and positions, since theory doesn't always translate to reality in the complexities of a non-rectilinear room. So I did a huge amount of experimentation, measuring each change. I used a dbx measurement mic and a simple little clean pre-amp for the measurements, and a RS SPL meter to sniff around for energy buildup.
So that's it. I think it shows that you really can get good results in very sub-optimal rooms with enough trappage and enough trial an error. The result sounds fantabulous in terms of the clarity of the low end. The bass is so smooth and full and consistent. It's quite a pleasure to listen to CDs in there now just for fun. I didn't do any listening after tonight's binge. I was too tired and sweating like a pig. So I'll take a listen tomorrow night and it should sound even better than before. I managed to narrow up the remaining cancellation considerably this time and get the rest even tighter than it was.