I asked the same question over on AA a little while back. I had seen the formula somewhere, then when I needed it I couldn't remember what site I saw it on:
http://www.realtraps.com/art_room-setup.htm
It's down near the bottom of the page.
If you really want to try something interesting, read this review of Eighth Nerve products, which also discusses Nathan Loyer's speaker positioning method. While I just started using his products, I also use absorption panels (not on first reflection points) and after following his method, the improvement in clarity was quite noticeable.
http://6moons.com/audioreviews/8nerve/8nerve_2.html
http://www.realtraps.com/art_room-setup.htm
It's down near the bottom of the page.
If you really want to try something interesting, read this review of Eighth Nerve products, which also discusses Nathan Loyer's speaker positioning method. While I just started using his products, I also use absorption panels (not on first reflection points) and after following his method, the improvement in clarity was quite noticeable.
http://6moons.com/audioreviews/8nerve/8nerve_2.html