New absorptive systems were proposed to control low frequency noise because porous material has bad noise control performance in low frequency. But this systems are required a long distance between rigid wall and absorptive systems in order to absorb a sound for low frequency. Therefore, it is necessary to supplement for shortcoming of these system.
In this study, a resonator system which can control low frequency noise is proposed and we study about the prediction method of theoretical absorption coefficient. As a preliminary experiment , absorption coefficient of resonator array was measured by reverberation room method. We confirm the fact that resonator array is able to absorb low frequency in the broadband noise. Therefore, it needs theoretical method that can explain the characteristics of resonator array.
First, input impedance of unit resonator is derived, and the averaged surface impedance of resonator array is expressed by using spatial average concept on the surface. The theoretical model shows good agreement with experimental result of impedance tube.
For random incidence, the absorption coefficient of resonator array is predicted on the assumption that surface of array is locally reacting surface. But the result shows difference between the experimental result of reverberation room method. When many resonators exist, input impedance of single resonator is sum of self-radiation impedance and mutual-radiation impedance. The results that consider interaction agree well with an experimental result of reverberation room method. Consequently, we can conclude that resonator array is a bulk reacting material and its absorption coefficient has to predict by consideration of interaction between resonators.
