However, the formula is in Robert Harley's book and should be available on Amazon. I do recall that he rates dimensions from best to worst and I was a little surprised as how small the ideal room size would be.

I have had very large, large, medium and small room systems....the smallest had the least problems to deal with acousticaly.  Maybe 20x16x8 might do it, with seating along the opposite long wall to minimize standing waves.

I am satified with my current room dimensions which are:  22'L x 13'W x 8'H. If I were to change anything, it would be the height of my room. I would like 12' ceilings will strategically placed ceiling diffusers in a T- pattern above my listening position.

http://www.cardas.com/content.php?area=insights&content_id=41&pagestring=Listening+Room+Dimensions

http://www.cardas.com/content.php?area=faqs&content_id=7&pagestring=Listening+Room+Design

20 feet in length Jeff.  I sit across from the speakers, with my back against the opposite wall, something John Dunlavy turned me on to.  My systems have never sounded better since Ihave  used his long wall placement suggestion.

I'm probably gonna butcher this, but in F. Alton Everest's book on acoustics, he mentions the "golden" ratio, or something like that.  Seems it was about 2.2:1.6:1 or there about...which could translate to a room dimension of 22x16x10...or 17.6x12.8x8...or if you have 12' ceiling, 26.4x19.2x12.