Moving Vehicle Noise Source Identification Method Based On Nearfield Acoustic Holography

The precondition of moving control is to identify the moving source accurately. At present, the main methods for identify the noise source have the elimination method, sound intensity measurement method, sound intensity measurement, near acoustic holography. In this paper, we identify the vehicle movement noise source by the near acoustic holography method.Acoustic holography field transformation technology measure the source pressure of holographic surface which surrounded by the holographic measurements plane, then use the relation of the space between the surface acoustic pressure and transform hologram to get real pressure of the Surface acoustic source. Because the singles get from the moving vehicle includes doppler effects, so doppler signal must be corrected before can be used for acoustic holography sound source position reconstruction.Previous researches are mainly used linear arrays of vertical to get the moving source noise at home and abroad.The foundation of this text is on linear arrays mikes of vertical, moreover, we used two linear arrays which are vertical to each other. The arrays are so-called cross-mike-arrays. The singles from the level array mikes within cross-mike-arrays interrelated with each others, singles from mike array of vertical doppler signals are correction. Then the acoustic holography method can be used to holographic reconstruction. Through testing and comparison of the reconstruction, the cross-mike-arrays method can reconstruct reliable sources, greatly improved positioning accuracy and reliability.The main results obtained in this paper:1, Analysis of the doppler effect caused by two main factor: the measurement mikes acceptable time interval finer signals from the sound source isn't radiating in interval of time, which led to the signal frequency shift. Because of the distance between the mikes and moving vehicle noise sources are changing by time, which result in the signal amplitudes changes follow the distances between the sources and mikes. According these reasons caused to the doppler effects. According to the reasons that cause the doppler effects, some methods are used to get originality messages of vehicle moving noise sources.2, Further study the theory of acoustic holography and it's discrete algorithms, discussed the green function which play a important role in acoustic holography, and are to discuss its features from space and real space. Discuss the reconstruction of the Green function of the distance and reconstruction frequency attenuation characteristics and the impact of the result. Discuss the reconstruction of the Green function of the distance and reconstruction frequency attenuation characteristics and the impact of the result.3,As a detailed source of the spread is derived from different, this time embodied in the corresponding signal delay .We related to stationary random signals, which includes delay time. After calculating the delayed time, a good combination of Mike spatial design, can be in any direction relative to the source of one-dimensional or two-dimensional direction of noise source position.4 Test is divided into two parts: Firstly, two single-frequency speakers on the different places of the vehicle. When the vehicle passed by two speakers also issued a voice frequency, and surface acoustic holography source of the sound source location for reconstruct, reliability and validity of the methodology. Secondly, in the last step to complete work on the basis of verification, the only difference is, we test to close loudspeakers, Vehicle location of the noise source and then rebuild.These methods have been used in actual experiments, the experimental results show that it has high value. These methods can be used to measure the noise and vehicle movement noise in the vehicle for positioning source of spectral analysis, evaluation of source characteristics.Then the corresponding measures on the sound source is obtained. It has very practical application values.