• Leclere, Quentin
• Lecomte, Pierre
• Belloncle, Simon

Abstract

Acoustic imaging is usually performed using a single array of omnidirectionalmicrophones distributed on a planar, cylindrical or spherical geometry. In thecase of spherical microphone arrays (SMA)s, the analysis can be done in thespherical harmonics (SH) domain, as developed in the field of Ambisonics.However, practical implementations of the latter approach are often constitutedof a smaller number of microphones compared to planar arrays, which implieslimited spatial resolution and bandwidth. This work deals with the use of 5 19- microphone rigid SMAs for the capture of their respective local sound field, anddiscusses on how to process them globally for acoustic imaging purposes. Fourstrategies are presented in a comparative study, by considering the distributedSMAs as: {list}a) an array of 519 omnidirectional microphones in freespace, not taking into account scattering from the rigid spheres,b) an array of 519 microphones mounted on diffractingspheres, scattering from the rigid spheres is taken into account,c) 5 distributed SMAs, each of them retrieving 16 SH coefficientsup to degree 3, and processed in the SH domain on all coefficients at once,d) 5 Distributed SMAs combined by translation of the local SHcoefficients on a global origin, capable of retrieving SH coefficients up todegree 7, and processed in the SH domain. {list}These processing strategies are evaluated in simulations and validated in theframe of laboratory measurements based of the use of 5 SMAs distributed on aplane, at the vertices of a pentagone. Acoustic imaging results are comparedwith a conventional planar microphone array constituted of 81 microphones.

Topics

• impedance spectroscopy
• simulation