The properties of the estimation error of sound power measurement using sound intensity techniques

Abstract

In this article, a general expression was derived for the sound intensity normal to a plane measurement surface caused by a plane distribution of monopole sources. A program was developed to calculate the ratio between the approximate sound power estimated from a finite number of measurements of sound intensity on a plane surface and the exact power passing through the same measurement area. The ratio, which is considered the estimation error of the sound power measurement, is affected by many factors such as the number of measurements, the distance between the source and the measurement surface, the locations of the sources with respect to the measurement points and the types of sources. The effects of these factors on the estimation error were investigated, and some error curves were plotted. By examining the error curves, it was found: (1) when the measurement surface has unit area, the estimation error decreases with an increase in the measurement distance and an increase in the number of sound intensity measurements; and (2) when the measurement surface is a surface enclosing the source, the estimation error depends on the total number of sound intensity measurements over the surface, and does not depend on the measurement distance or the number of measurements over each unit area. Some experimental tests were carried out to check the error curves for the case when the sound source is a monopole. The experimental results agreed well with the theoretical predictions.