Abstract
Microphone arrays methods are useful for determining the location and magnitude of rotating acoustic sources. This work presents an approach to calculating a discrete directivity pattern of a rotating sound source using inverse microphone array methods. The proposed method is divided into three consecutive steps. Firstly, a virtual rotating array method that compensates for motion of the source is employed in order to calculate the cross-spectral matrix. Secondly, the source locations are determined by a covariance matrix fitting approach. Finally, the sound source directivity is calculated using the inverse method SODIX on a reduced focus grid. Experimental validation and synthetic data from a simulation are used for the verification of the method. For this purpose, a rotating parametric loudspeaker array with a controllable steering pattern is designed. Five different directivity patterns of the rotating source are compared. The proposed method compensates for source motion and is able to reconstruct the location as well the directivity pattern of the rotating beam source.
Highlights
Beamforming techniques for the source localization of rotating noise sources have been widely applied in various industry applications, such as axially blowing fans, wind turbines and rotor blades
This work presents an approach to calculating a discrete directivity pattern of a rotating sound source using inverse microphone array methods
The inverse microphone array methods are based on the cross-spectral matrix, which can be calculated from the measured pressure signals pm of M microphones via
Summary
Beamforming techniques for the source localization of rotating noise sources have been widely applied in various industry applications, such as axially blowing fans, wind turbines and rotor blades. Frequency domain methods have been used to model propagation in a duct [3,4] and under free field conditions [5,6]. Common to all those techniques is the assumption of monopole sound sources. Since most aerodynamic sound sources have non-uniform directivity patterns, beamforming algorithms for rotating sources using monopole transfer functions may result in the incorrect estimation of positions and strengths of sources. A dipole directivity in the transfer function was introduced for beamforming algorithms [7] and applied to rotating sources using dipole sources with unknown orientations [8]. A correction method for ROSI with dipole sources was implemented in [9]
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