A Comparison Of Procedures In ISO Pressure And Intensity Standards For The Measurement Of Sound Power

摘要

EU machinery and outdoor equipment Directives provide an impetus for improvement of sound power measurement standards. This study compares the accuracy and efficacy of methods used in a sound power standard based on pressure measurement, ISO3744, versus a standard based on intensity measurement, ISO9614-1. The study used a systematic evaluation of the procedures in these standards. The use of pressure or intensity, as well as the number and location of measurement points were varied independently while the transducer was kept constant. This was achieved using a single set of triaxial intensity measurements, taken over a box-shaped measurement surface. Sound pressure was derived from each triaxial measurement, based on either ISO 11205, or the mean pressure. Measurements were made of three sources: a circular saw, a vacuum cleaner, and a reference sound source. Three acoustical environments were used: a hemi-anechoic chamber, an office and a reverberant stairwell. Accuracy was estimated by comparison with precision measurements as per ISO 3745. The number of measurement points, N, had the largest effect on uncertainty. For similar accuracy, the required N was the same for either pressure or intensity based standards. The indicator in the pressure based standard gave a better estimate of the N required to obtain the desired accuracy. In addition, using the intensity probe for pressure measurements allowed the simplicity of the pressure based standards to be combined with the benefits of an intensity probe.