It is well known that the acoustic properties of a concert hall have considerable impact on the enjoyment of a performance. There are a number of parameters that have been established as important in determining the subjective acoustic quality of an auditorium. One of the first to be recognised was the reverberation time [1], given approximately by

where A is the room absorption and V its volume [2] A second parameter of interest is the reverberant loudness, which can be quantified by the steady state energy density, obtained when the room is excited with a constant power W_in, [2]

where c is the speed of sound. These two parameters are “coarse”, in that they do not depend on the detailed temporal and amplitude distributions of the impulse response or on the spatial distribution of reflections arriving at a point in the room. Furthermore, they have approximately the same values for any source or receiving position in the room.

More recent research has shown that the fine structure of the sound arriving at a point in the room from a given source position is also important. For example, the subjective impression of quality is related to the amount of lateral energy reaching the listener in the early part of the impulse response; this lateral nergy introduces a sense of spaciousness to the sound [3]. A number of other parameters have also been described in the literature which are related to the temporal and spatial fine structure of the impulse  response [4-6]. These parameters are source and  receiver position specific, and are typically optimised  for sources in the stage area. The challenge for the acoustic designer is to optimise them for all of the receiving positions (ie seats) in the room. It is thus apparent that there are two thrusts to the acoustic design of concert halls; the first involving the control of the early reflection sequence for sources in the stage area and the second involving the non-source position dependent parameters - the absorption and volume - which control the steady state level and reverberation time.