Determination of sound pressure levels in situ using sound intensity measurements

Abstract

Measurements of emission sound pressure levels of machinery require either specially defined test rooms or calculated corrections for the acoustic environment. In principle, it is possible to determine emission sound pressure levels from sound intensity measurements at specified work stations in any test environment if the requirements of background noise levels and field indicators are fulfilled. The draft international standard ISO 11205/CD specifies such a method. In this paper the accuracy of emission sound pressure levels using sound intensity measurements was examined for three small sources in three acoustic environments, an anechoic environment with loudspeakers to simulate background noise, an office environment, and a reverberant environment inside a stairwell. In the first two environments good measurement accuracies, within 1 dB, were obtained. Sound intensity measurements by pointing the probe towards the source were as accurate, and simpler than computation of the resultant intensity using three arbitrary orthogonal measurements. As predicted by field indicators, measurements in the stairwell gave unacceptable errors for all three sources.