Conventionally, sound insulation materials have been applied to control interior noise above 500 Hz, and damping materials to control interior noise below 500 Hz. In this paper, the noise control component for vehicle panels, which consists of damping material and sound insulation material, is investigated by using a two-degrees-of-freedom system.
The investigation shows that sound insulation material can be effective in reducing interior noise below 500 Hz if its stiffness is reduced. This stiffness depends not only on the spring of the material itself but also on its pneumatic spring which is determined by air-flow resistance.
This paper concludes with applications of techniques to reduce interior noise below 500 Hz by improving sound insulation materials.