room acoustics question

Was reading the latest TAS or Stereophile and got to thinkng about room acoustics (again) and I have a couple of questions that the readers might be able to help with.
1) Is there a math formula that can be used to calcultae the arrival time (and hence help with room tuning) for driver responces? This may be even more difficult as I use Apogee Slant 6s and the radiation is bipolar. 2) Should the back of the room be kept "dead" or should I be using diffusion or reflection to increase the staging and depth? Currently the back of the room has somewhat thick curtins with 1 48" Room Tune opposite the right speaker, I also use 3 additional 48" Room Tunes (the use of them has been a huge help) behind the speakers as well as 4 Corner Tunes in my system, sound is quite good but I am looking to increase my over all experience when listening. I listen to Blues, soft Rock and New Age. (full system info can be seen in my listing). Your opinins would be helpful and naturally I'm trying to be cost effective as well with my choices. Thanks---Ray
Sound travels about 13500 inches per second. So if your dipoles are 4 feet out from the wall, the backwave's arrival is delayed by roughly (4*12*2)/13500 = 7.1 milliseconds relative to the frontwave, not factoring in angles.

I prefer diffusion of the backwave rather than absorption, unless your room is extremely live, and/or unless you are forced to place the speakers very close to the wall behind them.

My understanding is that a round-trip path length for the backwave energy sufficient to impose about 10 milliseconds time delay is desirable from a psychoacoustics standpoint. But this isn't a hard and fast rule; if you can't achieve that much delay, still get as much as you can.

In my experience if you are unable to place dipoles more than about two and a half feet out from the wall, absorption of the backwave (or switching to monopoles) starts to make sense.

Thanks for that info Duke that is a real help! I measured the distance from ribbon to front wall and it is approx 36-38 inches each. My right speaker has a coner placement and I have the 48" Room Tune approx 28" from the ribbon for diffusion, the left has 2 48" Room Tunes placed apporox 22" and 32" to form a quasi corner for that speaker and helped to bring the bass into much better definition and focus after many hours of moving and tweaking them into position. (I have since marked thier placements with tape on the rug). My further question comes into play concerning the back wall where it is deadened by the curtins. Should I also consider diffusion and or reflection for better staging and depth preception? If so I like the Room Tune products as they have been so easy to use yet so absolutely effective in thier performance (other product suggestions are also welcome). I am going to try to figure the wave responce thru your help with the formula provided to see if I could further improve the performance (Thank you for that!). So far it's been a lot of hours of tweaking and changing angles and spacing and beleive me when I say as much as 1/16" makes a very hearable difference when moving Room Tunes. Again Thanks very much for your observations and help so far.
A time delay of ten milliseconds or less is likely to be experienced as smeared sound. A fifteen millisecond time delay would be ideal for many people -- the brain will process it as if it were room or hall ambience.