Room Modes & Standing Waves
Room modes are resonant frequencies where wavelengths match room dimensions, creating standing waves with pressure antinodes and cancellation nodes. The first axial mode occurs at f = c/(2L) where c is 343 m/s and L is the room dimension in metres.
Types
Axial: between parallel surfaces, strongest. f(n) = nc/(2L). Tangential: four surfaces, half energy. Oblique: six surfaces, quarter energy. General formula uses all three dimension indices.
Schroeder Frequency
fs = 2000 sqrt(T60/V). Below fs, individual modes dominate. Above, statistical behavior. Small rooms: 150-300 Hz typically.
Distribution
Bonello criterion evaluates mode density per 1/3 octave. Ratios like 1:1.26:1.59 minimize clustering. Cubic rooms are worst.
Treatment
Bass traps in corners (all axial antinodes converge). Membrane absorbers for specific frequencies. Quarter-wavelength depth minimum. Multiple subwoofers reduce excitation via spatial averaging.
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Measure low-frequency room behavior