ABSTRACT
Reverberation is a phenomenon which plays a major role in every aspect of room acoustics and which as yet yields the least controversial criterion for the judgement of the acoustical qualities of every kind of room. It is this fact which justifies devoting the major part of a chapter to reverberation and to the laws which govern it. Another important subject to be dealt with in this chapter is the diffuse sound field. Both reverberation and diffusion are closely related to each other: the laws of reverberation can be formulated in a simple way only for sound fields where all directions of sound propagation contribute equal sound intensities, not only in steady state conditions but at each moment in decaying sound fields, at least in the average over time intervals which are short compared with the duration of the whole decaying process. Likewise, simple relationships for the steady state energy density in a room as will be derived in Section 5.5 are also based on the assumption of a diffuse field. It is clear that in practical situations these stringent conditions are met only approximately. A completely diffuse sound field can be realised fairly well in certain types of measuring rooms, such as reverberation chambers. But in other rooms, too, the approximation of the actual sound fields by diffuse ones is not too crude an approach. In most instances in this chapter we shall therefore assume complete uniformity of sound field with respect to directional distribution.
