751 Influence of expanding layer to oblique-incident sound characteristics of thermoplastics reactive type sound absorber by injection expanded molding

Abstract

We suggest the new method of oblique-incident sound absorption measurement by the ultrasonic waves. This method can be used also to measure the random and normal incident sound absorption. The area of the specimen may be very small. The oblique-incident sound characteristics of Helmholtz reactive type resonator depends on sound incident angle. The resonance frequency shifts high as the angle of incident sound shifts from normal. However the sound characteristics of resonator with inner porous core hardly depend on incident angle.