A Modal Analysis of Violin with Nearfield Acoustical Holography.

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We have developed a method using nearfield acoustical holography to measure velocity of a surface from the acoustic data radiated from it. We examined at first the parameters of the data acquisition by the numerical simulation and the experiment in the reduced size with high frequency to reconstruct properly the vibrating surface. They are the position of the plane, data acquisition region and the sampling intervals. Then using the results we have experimentally measured the vibration of a violin top plate. It is shaken by a vibration-tool and the radiated pressure field is measured on a plane near the plate. The velocity of the plate are reconstructed from the data, of which the nodal lines are almost the same of those once obtained by Chladni method. This means that our method is reliable. The resolution of the method is less than a hundredth of the wave length, because the about 7 mm width of the 'f-hole' of the plate could be reconstructed in the 'ring mode' of 335 Hz, of which wavelength is more than 1 m. These results will be presented at International Symposium on Simulation, Visualization and Auralization for Acoustic Research and Education (ASVA'97).