Page 158 - Master Handbook of Acoustics

FIGURE 7-8 Diffraction occurs around a solid sphere about the size of a human head. For sound in
the 1- to 6-kHz range, sound pressure is generally increased in the front hemisphere and reduced in
the rear. (Muller, Black, and Davis, as reported by Olson.)

Diffraction by Loudspeaker Cabinet Edges

Loudspeaker cabinets are notorious for diffraction effects. If a loudspeaker is placed near a wall and
aimed away from the wall, the wall is still illuminated with sound diffracted from the corners of the

cabinet. Reflections of this sound can affect the quality of the sound at the listener’s position.
Vanderkooy and Kessel computed the magnitude of loudspeaker cabinet edge diffraction. The
computations were made on a box loudspeaker cabinet with front baffle having the dimensions 15.7 ×
25.2 in, and depth of 12.6 in. A point source of sound was located symmetrically at the top of the
baffle, as shown in Fig. 7-9. The response from this point source was computed at a distance from the
box. The sound arriving at the observation point is the combination of the direct sound plus the edge
diffraction. The resulting response is shown in Fig. 7-10. Fluctuations due to edge diffraction for this

particular experiment approached ±5 dB. This is a significant change in overall frequency response