Room modes

Room modes are the collection of resonances that exist in a room when the room is excited by an acoustic source such as a loudspeaker. Most rooms have their fundamental resonances in the 20 Hz to 200 Hz region, each frequency being related to one or more of the room's dimensions or a divisor thereof. These resonances affect the low-frequency low-mid-frequency response of a sound system in the room and are one of the biggest obstacles to accurate sound reproduction.

Discrete room modes dominate only at low frequencies. Above a transition known as the Schroeder frequency, the modes overlap so densely that the room response is better treated statistically than as a set of separated resonances. This frequency is commonly approximated by

{\displaystyle f\approx 2000{\sqrt {T/V}}}, where T is the reverberation time in seconds and V is the room volume in cubic metres; for typical rooms it falls in the low hundreds of hertz.