ABSTRACT
This chapter discusses the measuring techniques for the evaluation of room performance. In small rooms, the truly diffuse sound-field required to produce reverberation can never develop, but the relative energy in the modes, discrete and diffuse reflexions all contribute to the overall perceived sound. The energy/time curve (ETC) is the result of applying a technique to a transient signal which does not depend upon time averaging, but which yields an estimate of a mean-square-like value, which varies with time. Some of the characteristics of the ETCs and the more conventional T60 plots can be combined into what is commonly known as a 'waterfall plot'. Short of building full-size prototype rooms, the next best possibility would seem to be to build and test scale models. The power of computer modelling seems to increase day by day, but computers still cannot design rooms. Light ray models have also been used in room analysis.
