Also called standing waves, room modes come in three types: axial, along the axes of a room (front to back, side to side, floor to ceiling); tangential, or any two pairs of opposite surfaces; and, oblique modes which are the product of the reflections of all six surfaces. To calculate the frequency of a particular mode
Where f is in Hertz, c is the speed of sound (1130 ft./sec. or 344 meters/sec.), L is the room di-mension, and n is the order of the mode. It’s not important to know the frequencies of the room mode, just how evenly spaced they are. If they are not uniformly distributed, the room will show a response peak where they are nearly coincident. The most problematic frequency range is 50Hz-150Hz. The golden ratios of height to width to length are: 1.14:1.39:1 or 1.28:1.54:1 or 1.60:2.33:1 (Bolt’s golden ratios), then the modes will be perfectly spaced and low-frequency response is smooth by design. See also standing wave.