Procedure for the Accurate Phase Calibration of a Microphone Array

Abstract

The “delay and sum beamformer ” algorithm (“DSB”) is a powerful tool for the locali-sation and quantification of acoustic sources with microphone arrays. For the calculation of beamforming maps the DSB algorithm requires the following input data: time series of all microphones, a grid of focus points which includes the region of interest, parameter of the flow for boundary layer or shear layer corrections and the accurate position of all microphones. The present paper is focused on the last item: the accurate estimation of the microphone positions. Especially for aeroacoustic applications the number of microphones should be large enough in order to obtain good beamforming results. The estimation of the accurate microphone positions can mean a huge time consuming effort. The method which will be presented in this paper is similar to the well known global posi-tioning system: distances to satellites provide information about the position of a receiver. Here, several monopole-like acoustical point sources with known positions and a reference microphone which is installed close to the sound sources are used to compute the position of the microphones of a microphone array in the three-dimensional space. After pointing out the basic concepts and algorithms a practical implementation of the