TABLE OF CONTENTS Diffusion problems are most troublesome in smaller rooms and at the lower audio frequencies. The problem with small spaces such as the average recording studio, control room, or music listening room is that modal spacings below 300 Hz guarantee a sound field far from diffuse (Chap. 15).
Even though unattainable, it is instructive to consider the characteristics of a diffuse sound field. Randall and Ward1 have given us a list of these:
The frequency and spatial irregularities obtained from steady-state measurements must be negligible.
Beats in the decay characteristic must be negligible.
Decays must be perfectly exponential, i.e., they must be straight lines on a logarithmic scale.
Reverberation time will be the same at all positions in the room.
The character of the decay will be essentially the same for different frequencies.
The character of the decay will be independent of the directional characteristics of the measuring microphone.
These six factors are observation oriented. A professional physicist specializing in acoustics might stress fundamental and basic factors in his definition of a diffuse sound field such as energy density, energy flow, superposition of an infinite number of plane progressive waves, and so on. The six characteristics suggested by Randall and Ward point us to practical ways of obtaining solid evidence for judging the diffuseness of the sound field of a given room.
There is nothing quite as upsetting as viewing one's first attempt at measuring...
