Page 182 - Master Handbook of Acoustics

FIGURE 9-7 Polycylindrical diffusers, when properly designed, are very effective at providing
wideband diffusion. (A) A polycylindrical diffuser reradiates sound energy not absorbed through an
angle of about 120°. (B) A similar flat element reradiates sound in a much smaller angle of about
20°.

It is important that diffusing elements be characterized by randomness. A wall lined with polys, all

of 2-ft chord and of the same depth, might be beautiful to behold, but is not very effective for
diffusion. The regularity of the structure would cause it to act as a diffraction grating, affecting one
particular frequency in a much different way than other frequencies, which is counter to the ideal of
wide-frequency diffusion.

Plane Surfaces

Geometrical sound diffusing elements made up of two flat surfaces to give a triangular cross section,
or of three or four flat surfaces to give a polygonal cross section, may also be used. In general, their
diffusing qualities are inferior to the cylindrical section.