Sound power determination using sound intensity: A review of the technique and the ISO 9614/1 standard

Abstract

The sound power emitted by a source with a highly directional behavior was determined using sound intensity measurements. The parameters varied were: number of measurement points, degree of reactivity of the measurement room, level of extraneous noise, shape of the measurement surface, and distance from source to measurement surface. Both the ISO field indicators and ISO criteria were examined. The relation between the changes in the ISO indicators and criteria and the accuracy obtained was studied. It was found that, for most of the cases, the requirements due to the values taken by ISO criteria did not have a correlation with the accuracy obtained in the measurement, especially those values of ISO criterion 2 (related to the statistical distribution of measured intensity). The statistical nature of this criterion is not the best way to indicate the accuracy of a sound power determination. Also, criterion 2 fails when there is an extraneous noise source. The influence of environment reactivity was found to be a limitation on the accuracy of the technique. The results obtained coincide with those obtained by various researchers around the world. [Work supported by the National Center of Metrology, México, and the Acoustics Laboratory of IRC-NRC, Canada.]