Microphone position localization with acoustic pulse sequences

Abstract

Microphone arrays of complex geometry are used at DLR Engine Acoustics, in order to conduct fly-over experiments with real aircraft or to conduct low-reflection acoustic measurements in laboratories or enclosures, with reverberating walls. The fly-over measurement are performed by adopting a multi-arm spiral array of over 200 microphones, laid across a large (over 20 m) elliptical spot on a surface made of tarmac or concrete. The laboratory measurements are performed by adopting a low reflection barrel, instrumented with an array of 12-microphone rings. The geometric complexity of both microphone distributions requires a time expensive measurement procedure, in order to determine the positions of the sensors in the array. A technique to realize an automated localization of the sensors has been recently implemented and tested. The automated microphone localization follows the work done by Dobler ¨ and Heilmann [2] and determines the microphone positions with respect to a sequence of point acoustic pulses distributed on an arbitrary three-dimensional trajectory. An electric-arc generator has been used, in order to introduce the sequence of acoustic pulses in a limited spatial region above the spiral array or in the interior of the barrel. The time-delay distribution between pulse generation and microphone reception can be used to reconstruct both the acoustic-pulse trajectory and the microphone positions, by applying a non-linear optimization technique. In the present paper, we show results for the microphone-position distribution in the laboratory barrel, as determined in an acoustic experiment at the DLR-Berlin inlet parasitic noise test rig.