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The door closing sound is one of the important quality of a vehicle, and it is useful to study the improvement method of closing sound. As a step to clarify the relationship between the door structure and closing sound, it is attempted to correlate the formation of closing sound with the vibration, and explained that the effect of structural modification aimed to improve the closing sound from the viewpoint of vibration. First, the formation process of the vibration during the door closing is clarified through the analysis method of transient vibration using the pulse laser holography. And the quality of closing sound are evaluated based on the time historical fluctuation of frequency characteristics. Next, the correlation between the closing vibration and sound are studied, and for the case of that the closing sound are changed by the structural modification, the correlation are confirmed.

For the booming noise reduction by vibration mode control, structural and acoustic analyses or optimization procedure have been studied. For obtaining know-how to reduce booming noise, it is necessary to understand the mechanism of vibration phenomenon, and then to simplify the phenomenon. In this paper, it is presented that the booming noise should be reduced by using the simplification of panel vibration mode of vehicle body. Simplification is obtained by considering that panels are forced and vibrated by the body frame of the vehicle, and that panel vibration is decided by frame movement and stiffness and mass distribution in the panel. The simplification about panel vibration control by the appropriate mass and stiffness distribution is confirmed by using floor vibration. By appropriately controlling the stiffness distribution in the dash panel, booming noise caused by the dash panel vibration was reduced.