Hopefully someone can post some good links, but the basic idea is that bass reinforcement is a result of standing waves between the walls or ceiling/floor of your room. A standing wave happens when the wavelength (or 2, 3, 4.. wavelengths) is equal to the round-trip distance between the surfaces.
You can see where this is going. Speed of sound is ~1130 feet per second (1120, 1135, whatever). Let's assume you have 14 feet between walls, 28 feet round trip. You get a peak at 1130/28 or 40.4 Hz, plus all the multiples of 40 hz (80, 120 etc...).
You can either divide 1130 by the round trip distance (there and back) or divide 565 by the one-way distance. Same thing.
You get dips when the round trip distance is half a wavelength or any multiple. Simple rule of thumb is :
1130 / twice distance gives you the frequency of the first peak, with subsequent peaks at 2x, 3x, 4x... the frequency, each peak being less of an issue. Same for each pair of walls. Angles are hard, ask a pro with a computer simulation
Half the frequency of the first peak gives you the frequency of the first dip, plus the ODD multiples of the first dip
14 feet between walls gives you peaks at 40, 80, 120, 160... and dips at 20, 60, 100, 140...
Do a search for "modecalc" and "download" or I'll post a link tonight.
