A comparison of popular beamforming arrays

Abstract

Beamforming is a popular method of acoustic source localisation using an array of microphones. When beamforming over a plane or a series of planes, these microphone arrays are often two-dimensional sparse patterns of various designs. The design of these patterns is non-trivial, and influences the achievable resolution, also referred to as the beamwidth, and the Maximum Sidelobe Levels (MSL), a measure of the ability of the array to reject sources that the array is not focussed on. Although recent deconvolution techniques such as DAMAS aim to remove properties of the array from the results of beamforming, in practice the properties of the array will still influence the quality of the results. For this reason, it is important that the array exhibit good resolution and MSL for the intended beamforming application. In this paper, several popular two-dimensional array patterns such as the patented Underbrink and B&K spirals, as well as Doherty spirals and log-spirals are critically compared for both resolution and MSL for a variety of source locations, including both near-field (spherical propagation) and far-field (planar propagation) sources. Each array compared has an aperture of 1m, and uses 63 microphones in a typical arrangement found for each of the types. As array resolution scales linearly with wavelength, the resolution is calculated at a single frequency of 3 kHz, and normalised against wavelength. The MSL levels are calculated at the one-third octave band centre frequencies from 1–31:5 kHz. Results show that the Underbrink design outperforms other array patterns in both resolution and MSL over the majority of frequencies analysed.