Measurement and Fourier-Bessel analysis of loudspeaker radiation patterns using a spherical array of microphones *

ABSTRACT Loudspeakers are widely used in three-dimensional sound field reconstruction systems, but their spatial directivity features are relatively little-known. In this paper, a hemispherical array of 40 microphones was designed and built in order to measure the pressure field radiated by different commercially available loudspeakers. The spatial samples of the acoustic pressure were processed in order to estimate the truncated Fourier-Bessel expansion of the sound field, which allows the reconstruction of the 3D radiation pattern. An analysis of the errors involved in the estimation was also performed with a numerical model of the array. 1. INTRODUCTION When an acoustic source radiates sound, it generates a sound field, which can be mathematically described by a scalar function, depending on both space and time. This paper presents a method for the measurement and numerical reconstruction of the sound field generated by a loudspeaker in free field. The simplest source of sound can be said to be a monopole source: it radiates sound equally in all directions and the sound field due to this source varies only as a function of the radial distance from the source. However, a loudspeaker is a more complex source and the sound field that it generates