Data on the performance of five different types of structures for use in echo‐free (anechoic) chambers are presented. The best one of these structures is shaped like a wedge and manufactured from glass fibers held together by a binding agent. When mounted in the room, the wedges are spaced out several inches from the walls, and the dihedrals of adjacent units are turned through 90°. Generalized specifications for the optimal design of structures made from glass fiber wedges are presented in terms of either (a) lowest frequency at which 99 percent or better absorption is desired or (b) maximum depth of treatment which may be installed in the room. The application of these specifications to two rectangular rooms is shown and inverse square law measurements performed in the two completed chambers are presented. In the larger chamber the deviations are within ±0.3 db out to 10 feet and ±1.0 db out to 30 feet from a point source of sound. In the smaller, the deviations are within ±1.0 db out to 10 feet.

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