design and manufacture of miniature co-incident microphone arrays

Co-incident microphone arrays are formed by arranging microphones very close together so that they are effectively co-located. The arrangement of the microphones is such that a 3D recording of the soundfield can be achieved. One example is an Acoustic Vector Sensor (AVS), whereby 3 pressure gradient microphones are used and arranged orthogonally to capture the x, y and z components of the directional sound pressure. Alternatively, the B-format microphone as used in Ambisonics audio, contains (typically) 4 hypercardioid microphones located at the corners of a tetrahedron; x, y and z signals are then formed using standard equations that involve subtraction of signals recorded by the microphones at opposite corners of the tetrahedron. Both the AVS and B-format designs rely on highly accurate placement of the microphones to ensure the resulting polar patterns are optimal in regards to the theoretically desired patterns. This becomes increasingly difficult as the size of the array becomes small. Hence, in this research, we have investigated the use of 3D modeling and printing to create structures that allow for highly accurate placement of the microphones. We have also researched solutions to improving the performance of the B-format microphone across a broad frequency range, including a three-tiered design where each tier is a tetrahedrally arranged set of microphones capturing a particular frequency range. Pictures of our designs and an indication of the performance are illustrated below, with more details to be found in [1].

Relevant Publications

[1] Dabin, M., Ritz, C.H., Shujau, M., “Design and Analysis of Miniature and Three Tiered B-format Microphones manufactured using 3D Printing”, Proc. IEEE 2015 International Conference on Acoustics, Speech and Signal Processing (ICASSP'2015), pp. 2674-2678, Brisbane, Australia, 19-24 April 2015.