Noise source identification by using near field acoustic holograpy and focused beamforming based on spherical microphone array with random unifrom distribution of elements

Abstract

With the development of techlology, noise controlling has received wide attention in recent years. Noise source identification is the key step for noise controlling. Spherical microphone array, which can locate the noise source of arbitrary direction in three-dimensional space, has been widely used for noise source identification in recent years. Conventional methods of locating noise source include spherical near field acoustic holography and spherical focused beamforming. The acoustic quantities are reconstructed by using spherical near field acoustic holography method to realize the noise source identification, while the noise source can also be located by using focused beamforming based on spherical harmonic wave decomposition. However, both these methods have their own limitations when they are used in identifying the noise source. Spherical near field acoustic holography has low resolution at high frequency with a far distance from noise source to measurement array for noise source identification, whereas the spherically focused beamforming has low localization resolution at low frequency. Noise source identification is discussed here, and a 64-element microphone spherical array with randomly uniform distribution of elements is designed. The combination methods of noise source identification by using spherical near field acoustic holography and mode decomposition focused beamforming are investigated. The performance of the proposed combination method is simulated, and an experiment on noise source identification is carried out based on the designed spherical microphone array to test the validity of proposed method. Research results show that the high-resolution noise source identification can be achieved by using near field acoustic holography when reconstruction frequency is 100-1000 Hz with a distance 0.3-0.45 m from noise source to the center of spherical array, while high resolution of noise source localization can be achieved by using spherical wave decomposition beamforming when signal frequency is 1000-5000 Hz with a distance 0.5-3 m from noise source to the center of spherical array. Spherical array with random uniform distribution of elements maintains stable identification ability in all bearings. The spherical near field acoustic holography has high-resolution distinguishing ability in near field and at low frequency, while the focused beamforming method has high-resolution distinguishing ability in far field and at high frequency. Therefore the noise source can be efficiently identified by using the proposed combination method of near field holography and focused beamforming with less elements and small aperture spherical microphone array.