An investigation into the relationship between sound intensity and normal surface velocity

Abstract

The analysis of sound characteristics using boundary element methods (BEM) requires accurate sound source data of normal surface velocity or pressure as boundary conditions. However, direct measurements of normal surface velocity are not easily acquired while sound intensity measurements are relatively easy to obtain. In this study the relationship between near field sound intensity and normal surface velocity is investigated. The study first considers correlated and uncorrelated sound sources in the frequency range of 63 to 1000 Hz. A matrix of sound intensity measurements on well-distributed points in the near field of the sound source is collected. A model of the relationship between sound intensity and volume velocity is developed and used to compute the normal surface velocity of the sound source from sound intensity measurements. The normal surface velocities are then used as the boundary conditions for a BEM model of the sound source that predicts the sound intensity at the original measurement points. The measured and predicted values are compared in order to validate the model. The differences of predicted and measured sound intensities that are within ±3 dB are considered sufficiently accurate.