Page 179 - Master Handbook of Acoustics

FIGURE 9-5 Graphical presentation of the reverberation time variations of the data of Table 9-1.
The standard deviation, expressed as a percentage of the mean value, shows lack of diffusion,
especially below 250 Hz.

Geometrical Irregularities

Researchers have studied what types of wall protuberances provide the best diffusing effect.
Somerville and Ward reported that geometrical diffusing elements reduced fluctuations in a swept-
sine steady-state transmission test. The depth of such geometrical diffusers must be at least one-
seventh of a wavelength before their effect is felt. They studied cylindrical, triangular, and

rectangular elements and found that the straight sides of the rectangular-shaped diffuser provided the
greatest effect for both steady-state and transient phenomena. Other experience indicates superior
subjective acoustical properties in studios and concert halls in which rectangular ornamentation in the
form of coffering is used extensively.

Absorbent in Patches