Design and Analyis of Reverberant Room Experiments

Abstract

Accurate measurements of sound power in a reverberant room using the substitution technique require that the means of the squared sound-pressure level (SPL) of the known source and unknown source be determined. Careful design of an experiment permits the errors due to the microphone traverse, the instrumention, and the source location to be separated. The technique of two-way analysis of variance with replication applied to a measurement of the SPL established by an air-conditioning condensing unit with only the fan operating reveals that (1) the observed variance in SPL is considerably greater than that observed for the Ilg Reference Sound Source and (2) strongly dependent on source location, with a small change of source location causing noticeable changes in the measured SPL. The variance due to source location for the 250-Hz 13-oct band suggests a pure tone exists in this band. Further experimentation shows that changes of a few degrees in the room temperature can also cause appreciable changes in the measured SPL for this band. Investigations of the details of the fan spectrum are continuing. Results of these experiments indicate that accurate measurements in a reverberant room require careful attention to details.