Calibration Of Acoustic Microphones And Array

Acoustic microphone array technology has become a powerful method for noise detection of mechanical machinery,and the accuracy of sound source localization based on array signal processing is closely related to the array performance.However,due to the inconsistency of the manufacturing process of microphones,the frequency response function can vary among microphones.On the other hand,the machining error of the array bracket and the mounting error of the microphone both make the actual positions of the array microphones deviate from their designed value.In addition,the frequency response characteristics of the microphone will degrade or even fail along with the service time.In this context,the calibration study of acoustic microphones and their array is carried out in this thesis,which is listed as follows:First of all,a calibration test platform of the microphones and its array is established.A sound source which emits swept-frequency excitation is developed,and the digital microphone array and its auxiliary testing accessories are designed;a data acquisition program of the analog microphone is developed based on MATLAB,and the data acquisition for the digital microphone is also studied based on the UDP protocol.The feasibility of the built test platform is verified by performing acoustic testing experiments with analog microphones and different types of digital microphones.Secondly,based on the comparison method in IEC 61094-5,a calibration test method for the frequency response of microphone is established.By placing the reference and test microphones in the same sound field,the calibration of the microphone under test is transformed into an estimation of the relative transfer function between these two microphones.The relative transfer function estimation methods based on time-frequency analysis and spectral estimation methods are studied,respectively,and the estimation accuracy of the algorithms is analyzed by simulation.The microphone calibration experiment is carried out,and the enhancement of a harmonic acoustic signal is moreover performed with the calibrated microphones,which verifies the feasibility of the proposed method.Finally,the phase calibration,anomaly detection,and position calibration of microphone arrays are studied.In the anechoic chamber environment,a calibration factor is obtained based on the cross-spectral matrix of the array to achieve the compensation of the phase offset.Based on the power spectral density function of the microphone signal,a correlation analysis is applied to realize the in-situ detection of abnormal microphones.The calibration scheme of microphone positions is studied,and a microphone position identification method based on time delay estimation and nonlinear least square fitting is established.The feasibility of the microphone calibration and detection algorithm is explored by conducting simulation and experimental tests.By undertaking the research work in this thesis,the principles and algorithms involved in the calibration of microphones and their array are studied in-depth,which is certainly useful for the development of high performance microphone arrays.