A Comparison Of Procedures In ISO Pressure And IntensityStandards 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 efficacyof methods used in a sound power standard based on pressure measurement, ISO3744, versus astandard based on intensity measurement, ISO9614-1. The study used a systematic evaluation of theprocedures in these standards. The use of pressure or intensity, as well as the number and location ofmeasurement points were varied independently while the transducer was kept constant. This wasachieved using a single set of triaxial intensity measurements, taken over a box-shaped measurementsurface. Sound pressure was derived from each triaxial measurement, based on either ISO 11205, orthe mean pressure. Measurements were made of three sources: a circular saw, a vacuum cleaner, and areference sound source. Three acoustical environments were used: a hemi-anechoic chamber, anoffice and a reverberant stairwell. Accuracy was estimated by comparison with precisionmeasurements as per ISO 3745. The number of measurement points, N, had the largest effect onuncertainty. For similar accuracy, the required N was the same for either pressure or intensity basedstandards. The indicator in the pressure based standard gave a better estimate of the N required toobtain 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.