A tunable sound absorber with perfect sound absorption for suppressing acoustic waves of different intensities

Noise reduction problem has been studied for decades with various novel sound absorbers proposed. Most existing absorbers are designed with fixed parameters, which cannot preserve a high absorption coefficient for acoustic waves with different sound pressure levels. This work designs a tunable sound absorber with a synchronously controlled neck and cavity to accommodate acoustic waves with different intensities. A nonlinear impedance model of the acoustic absorber based on an equivalent fluid method is established to quantify the relationship between the geometrical parameters, the levels of incident sound pressures, and the impedance of the absorber. Experiments on sound absorption performance are carried out to confirm the design and theoretical analysis of the absorber. The results show that the proposed absorber can maintain perfect sound absorption at designed frequencies by enlarging the cavity depth when the intensity of the acoustic wave increases. The sound reflection coefficient of the absorber is analyzed in a complex frequency plane. It is found that the sound absorption bandwidth of the absorber can be broadened with an increase in the sound excitation intensity as a larger cavity depth improves the upper bound of the sound absorption bandwidth. Physical insights into the energy dissipation mechanism of the absorber subject to different levels of sound excitation are provided. This work establishes a new approach to realizing perfect noise suppression performance of the absorber under different sound pressure levels without remanufacturing.