A Guide to Subwoofers - Blu-Ray Forum - Part I - Characteristics, Placements, Adjustments, etc.

Part II - Standing Waves & Room Modes

These are both very good posts and refer back often to Dr. Toole's research on the topic. (advance warning, they're both long posts and get fairly technical at times)

Charles - there is some good info in the second post about using and setting up multiple subs that you might want to read through.

Jason

Epic 80-800: HG Cherry