Two books by F. Alton Everest should be required reading: (1) The Master Handbook of Acoustics, and (2) Sound Studio Construction on a Budget. In (1), Everest analyzes main room nodes for a room very close to yours in dimensions, and you can see how to do it for yours and maybe change things for the better. (2) is about 10 years newer than (1), and is a lot more up-to-date on RPG-style acoustic treatment. If you want DIY info on those devices, I make them out of Styrofoam and could email you theory-and-practice sheets.
building a room from the ground up...
I'm looking for listers experiences in building their dedicated listening rooms. We will be building down the road and I want to make sure I don't overlook anything easy to do during construction that will aid in great sound after completion. Room will be approx 14' x 20' w/ 9' ceiling. I am already planning separate AC feeds for the room divided into 4 clusters, each on its own dedicated breaker( cluster for Digital, Amps, other audio, and lights.) What I would love is some real world advice on construction technique to make the room extremely solid and relatively soundproof to the rest of the house. Right now, I've heard good things about spacing all support joists and studs closer together that required and varying the distance between them to get different size cavities behind the sheetrock. Double sheetrock has been suggested. Anything that works, I'm willing to experiment with. Bring on the crazy and the not so crazy ideas. Please try to stick to normally available materials (no kevlar walls, etc...). Additionally, I'd like to hear of experiences in how to design a good sounding (natural sounding)room. I've looked at live end dead end, no parrallel walls, etc., but solicit any opinion. Thanks for all responses.