Sound Field Assessment by Measurement of Sound Pressure Distribution Close to Machine Noise Source : Estimation of Normal Particle Velocity at an Aperture by Single-Plane Sound Pressure Measurement

Abstract

For the assessment of machinery noise, we describe a method of estimating the normal particle velocity distribution from a sound pressure distribution measured at a single aperture close to the sound source based on near acoustic holography(NAH). In NAH, it is required that the distance between the surface of the sound source and the measurement aperture is one-tenth of a wavelength. In practice, the distance between the machinery and the measurement aperture is too large for NAH because of the 3-dimensional features of the machine, so this method is investigated under the condition that the sound pressure is measured at about one wavelength from the sound source. The size of the measurement aperture was determined to be 1m×1m. Through investigation by simulation, it has been shown that the effect of evanescent waves should be taken into consideration. Experimental verification shows that this method can be practically applied in echoic situations.