Is diffusion in concert halls a property of the volume or of the surface?

For nearly a century, the principal concept of the theory of concert halls has been that of a nearly uniform field of energy, generated by many reflections, that varies but slowly with time. This supposed uniformity and isotropy gave rise to the term “good diffusion,” a property of the volume; it is difficult to quantify. An alternate approach is to apply the photometric concept of diffuse reflection at the surfaces: This is readily quantified, permits calculation of intensity at the audience, and posits nothing about the properties of the volume. Microcomputer programs to implement the concept are at hand and have been applied to a study of Boston Symphony Hall, renowned for its highly diffuse ceiling and walls. Modeling techniques, also borrowed from photometry, are available too: 1/50th scale architectural models are eminently suitable; note that models employing mirrors—specular reflectors—are not accurate representations of good concert halls.