Implementation of a 64 channel microphone array

Diploma thesis (9.542KB)

Beamforming, or spatial filtering, is a useful technique for designing a directivity pattern with microphone arrays. For this application at least two microphones are required. To improve spatial resolution the number of microphones needs to be further increased. This is the motivation throughout this thesis, to implement a low cost planar microphone array with 64 channels. The basic configuration is an 8 times 8 grid with variable spacing inbetween the grid points. This offers a varity of different geometric layouts with 64 microphones. A challenge, however, is to determine the positions of the 64 microphones in space. Consequently, the geometry shall be captured automatically. For this purpose, loudspeakers are placed in space at known positions. This work employs a tetrahedral source arrangement as stable spatial construction. On the vertices of the tetrahedron four loudspeakers are mounted. Every loudspeaker individually transmits a measurement signal towards the microphone array. The acoustic delay to every microphone is determined with generalized cross correlation phase transform (GCC-PHAT) and with linear regression. At the given speed of sound the acoustic delay corresponds to the length of the paths. From the path lengths the coordinates of the microphones in space are determined with a numerical method (Simplex Method). The coordinates are required for an implementation of delay and sum beam formers or nearfield acoustical holography (NAH).