Abstract: To control the interior low frequency noise of cars, body structure improvement is time consuming by existing methods. So one new design method of body to lower interior noise is studied, by which the weak region of body could be quickly and accurately located. And it also points out the adjustment direction of body stiffness. The analytical function of interior sound field of the cavity is divided into five parts. By analyzing their characteristics, the six key combinations are gotten for studying the determinant parameter of sound pressure level(DPSPL). A simple coupled system of a rigid box with one flexible wall is used to analyze the relationship among the six key combinations. Then it is found that the product of the mode shape coupling coefficient, the frequency overlap coefficient and the proportion of structure mode at the driving point, could stand for the interior sound pressure level. It is DPSPL of the simple coupled system. The features of DPSPL are discussed in detail which fulfill the expected objective. Then by DPSPL the new design method of body to lower interior noise is achieved. By the new method the interior sound pressure level of a car is lowered. The results of further frequency response analysis show that after improvements of body structure the sound pressure level at the driver’s right ear is lowered by 3 dB on average and 10 dB at the most.

Key words: Determinant parameter of sound pressure level, Frequency overlap coefficient, Mode shape coupling coefficient, Structural-acoustic coupled system of car body, Vehicle