3D Beam Forming Measurements Using 3D-Microphone Arrays

Traditional acoustic measurements inside any cavity have historically been conducted with a small number of microphones. By this means it is possible to gain information about parameters like frequencies, orders and sound pressures. However, a space-selective analysis is nearly impossible and it is not feasible to find the position of the sound sources in space in a practical way. While traditional beam forming systems with planar microphone arrays have enlarged the possibilities of acoustic measurements, they do not give comprehensive information about the sound sources in the entire vehicle interior. Therefore, the components of the Acoustic Camera of the GFal were extended by a spherical, acoustically transparent and omni-directional array. A new option is to map onto a common 3D-CAD-model of the object of interest, for instance a vehicle interior.

The advantages and disadvantages of 2D- and 3D-mappings will be discussed in the paper. Furthermore, the important issue of positioning an array at first in the coordinate system of the 3D-model and secondly in the actual cavity which is to be measured will be addressed. The paper discusses the geometric and acoustic properties of microphone arrays which are applicable for complete 3D-measurements and mappings of interior and exterior structures. A practical way of determining the array's position and direction related to the measurement object will be proposed. Relevant examples will highlight these issues.