Absorption Technique for Road Noise

It is becoming common in recent years to take measures on vehicle interior noise by balancing other performances or by using acoustic materials that are advantageous in terms of weight and cost. However, acoustic materials for vehicles are mainly for reduction of high-frequency noise in the vehicle interior, and are not realistic measures for mid-frequency noise including road noise where reasonable thickness is needed. In this study, therefore, we identified the condition to reduce mid-frequency sound by focusing on the mechanism to reduce particle velocity as the sound absorption principle of acoustic materials and by utilizing acoustic materials in thin sheets used as a measure on high-frequency sound. We further derived the specific structure to realize this condition in order to reduce road noise.