The effect of wall shape on the decay of sound in an enclosure

A two-dimensional room is considered in which three of the “walls” are straight and the fourth has small, regularly spaced symmetrical projections. The method of Feshbach [1] is applied to determine the effect of the projections on the natural frequencies and normal modes of the room; explicit formulae are obtained for rectangular, circular and triangular projections.

Recent experimental results obtained by the B.B.C. Research Department [2] suggest that studios or halls with rectangular coffering may have superior subjective properties to those having other types of projection with comparable dimensions. The results here given appear to provide a theoretical reason for this superiority of rectangular coffering.