A fractal tetrahedron microphone array for the sound source localization

Abstract

Acoustic source localization has been practiced for structural health monitoring in industries, speaker recognition in ASR, etc. Due to the recent algorithmic and application advance of artificial intelligence, the limitations of conventional localization techniques have been overcome technically, e.g., using multiple hidden layers1. However, the physical limitation, such as the irregular directional response of the microphone array, remains a problem to be solved. The three-dimensional acoustic intensimetry (3DAI) is suitable for estimating the DoA of the sound source using a compact probe module, thus useful for mechanical systems involving narrow space. Even though its history is rather long, it has not been popularly used due to the significant inherent bias errors, which depend on the actual DoA of the source. Recent research showed ways to overcome the spatial bias error by using double tetrahedron modules2. However, the double-module compensates for irregularity of array directional response (ADR) for specific directions by increasing the number of microphones, which causes a shadow zone in the source localization. In this work, a method for enhancing the precision in source localization is suggested by using multiple probe modules to go beyond the capacity of the double modules. A fractal tetrahedron array is designed to possess four sub-layouts with different ADR, and an array combination method3 is applied to compensate for the spatial bias error. Figure 1 shows the layout of the designed microphone array and exhibits the ADR for kd=3.0, where d is the distance between adjacent microphones. Because the gradient of ADR is proportional to the localization error, one can think that the combined module has less error than the single module. Also, one can estimate the position of the source by estimating the source distance by calculating the nearest intersection point between the 3D intensity vectors4. A fractal tetrahedron array implementing the 3DAI using 10 microphones (B&K 4958) is constructed, fitting into the ABS frame fabricated using the 3D printer. Here, the microphone spacing is d=0.08 m. A localization test is conducted in an anechoic chamber to estimate the DoA and distance of the source. A band-limited white noise in the range of 0.5<kd[removed]