EVIDENCE OF DIFFUSE SURFACE REFLECTIONS IN ROOMS

In a recent publication [M. Hodgson, J. Acoust. Soc. Am. 84, 253-261 (1988)], predictions were compared with measurements made in an empty scale-model room and in various nominally empty factories and gymnasia. Consistent deviations between prediction and experiment were found. In order to explain these deviations, it was hypothesized that diffuse surface reflections were occurring in the test rooms. To test this hypothesis, further predictions have now been made using a ray-tracing model that takes diffuse surface reflection into account. It was found that excellent agreement between prediction and experiment is obtained as follows: (a) in the scale model, if all surfaces are 10%-40% diffusely reflecting; (b) in nominally empty factories, if the ceiling and walls are 60%-90% diffusely reflecting. This result represents strong evidence that typical untreated room surfaces are strongly diffusely reflecting.