Sound Engineer's Pocket Book, 2nd Edition

8  Acoustics

Resonant Frequencies in Rooms

Rayleigh’s formula for the frequencies of modes in a rectangular room:

where n_L, n_W and n_H are positive integers, including 0, L, W and H are the room dimensions and c is the velocity of sound.

Modal density. If the number of resonant modes N below the frequency f is fairly high then a reasonable approximation is given by

where	V is the volume,
S is the total surface area, 2(LW + WH + HL) and
L is the sum of the edge lengths 4(L + W + H).

Reverberation time (RT, r.t. or T₆₀)

This is defined as the ...