Experimental modal analysis technique for three-dimensional acoustic cavities

Abstract

This paper substantially advances Nieter and Singh’s acoustic modal analysis technique [J. Acoust. Soc. Am. 72, 319–326 (1983)] which used the coincident-quadrature response method to extract acoustic global properties of one-dimensional systems. Here a technique to identify modal parameters including damping of a three-dimensional cavity is proposed. The cavity is excited by a convertible acoustic driver whose volume velocity is monitored. Acoustic transfer impedance database is obtained for a number of cavity boundary locations which are chosen such that all modes of interest can be adequately described. The vector diagram method is used to fit the measured database in the neighborhood of each resonance frequency with a circle. The experimental technique proposed here has been verified by applying it first to a cylindrical cavity whose exact eigensolutions are known. Then for an annularlike cavity, experimentally extracted natural frequencies and pressure mode shapes are found to agree well with the results of a finite element model. The significance of this paper lies in the successful demonstration of an experimental technique which can be used for diagnosing the acoustics of irregular shaped cavities. The proposed technique also offers an alternative to the finite element method for acoustic modal analysis of three-dimensional ducts and resonators of irregular shapes and/or with complicated boundary conditions.