20907 Noise Reduction by Helmholtz Resonator with Acoustic Material Inside

Helmholtz resonator is a device for noise reduction. It is effective for noise that has a dominant frequency component. However, in some other frequency components, Helmholtz resonator makes the sound pressure increase. In some cases, it is necessary to reduce the effective sound pressure. In this study, acoustic material is inserted to Helmholtz resonator for damping, and the resonator is applied to a sound tube for a basic study. As a result, the SPL is reduced using acoustic material. However, it is considered that the optimal reduction effect has not been obtained and it is necessary to change the resonant frequency of Helmholtz resonator. Next, the optimal value of the resonant frequency and the damping ratio of Helmholtz resonator is found, using identification of modal parameters and the theoretical formula of dynamic absorber's FRF.