Improvement of noise reduction performance by decreasing air-flow resistance ff sound insulation materials

Abstract 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 acoustical materials for vehicle panels, which consists of damping materials and sound insulation materials, are investigated by using a two-degrees-of-freedom system. The investigation shows that sound insulation materials can become effective to reducing interior noise below 500 Hz byducin their stiffness. This stiffness depends on not only the spring of the material itself but also on the pneumatic spring which is determined by air-flow resistance. This paper concludes with applications of techniquws to reduce interior noise below 500 Hz by improving sound insulation materials.