Moved my computer room today, so a bit late on the responses.

E'pin is right, I was just trying to create a simple mental picture of basically what goes on.. Frankly, there is NO way to measure room modes based on calculations alone. It has to be done with a substantial amount of equipment.

I did mean to say the size in ft, not speed in ft, my bad.. and my guess may be off by a foot or two, it was just done from memory.. It still stands that a 55ft sound wave will bounce off flat hard surfaces a number of times before dissipating..

My theater room was designed with 8" thick walls of heavy insulation and when you stand in the room and talk, it is extremely dead, no reflected sound.. There are a number of absorbing an reflecting surfaces that affect the way sound acts in the room.

The best advice I can give is large flat hard surfaces are the worst... Do what you can to break up those surfaces, beams help, soft materials helps, carpet helps and if you have a projector, put in heavy curtains on the front wall. I am still working on those, I don't sow..