Room modes

Resonating sound wave in a closed room 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 f ≈ 2000 T / V {\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. Mechanism of room resonances Room modes between two hard walls. There must always be a sound pressure antinode at the walls. The input of acoustic energy to the room at the modal frequencies and multiples thereof