Prediction methods of radiation sound pressure using line array microphone are investigated. They can be applied to the three different physical situations. The first possible physical situation is that both noise sources and line array microphone are stationary, the second one is that the noise sources are stationary but the line array microphone moves with constant velocity, and the third one is that the noise sources move with constant velocity but the line array microphone is stationary.
In case of the first possible physical situation, it is known that Kirchhoff-Helmholtz integral equation cannot be applied to the prediction of radiation sound pressure using measured pressure or velocity information by line array microphone. To accomplish estimation method in this situation, free space sound field is decomposed into its eigenfunctions in spherical coordinates and rearranged according to the order of spherical Hankel function. Then the estimated radiation sound pressure can be computed using the coefficients of spherical Hankel function which is obtained from the measurement of sound pressure by line array microphone. Due to the characteristics of spherical Hankel function there is no discrimination according to the order of this function in the far field. Therefore, to reduce estimation errors in real situation it is suggested that the pressure should be measured in the transient region of the near field and the far field.
The second and the third situation are very similar each other and related to a simple coordinates transformation. To use the near field acoustic holograpy as a radation sound pressure estimation method the restoration method of hologram from the measured pressure by line array microphone is also investigated because they can be regarded as a sort of plane measurement. Two experiments are performed to verify these two methods. One is pure tone speaker experiment to verify the method applied to the second situation and the other is moving vehicle experiment related to the third situation. Through these experiments the method of hologram restoration is verified and the noise sources of moving vehicle are detected.
