Acoustic plate-valve resonator for low-frequency sound absorption

An acoustic plate-valve resonator is developed and optimized to maximize absorption by enhancing the Helmholtz resonance with coincident structural vibrations of the plate-valve. The current research initially examines the concept experimentally with a 3D printed valve. Then with the use of analytical and numerical modeling, a structural analysis is performed, which allows the eigenmodes and eigenfrequencies of the plate-valve to be determined. When the resonator properties are modified by changing either the depth of the backing cavity or the thickness of the plate-valve, the system can be designed in such a way that the Helmholtz resonance can be coincident with a particular eigenfrequency, leading to absorption higher than that achieved in the absence of such a flexible plate-valve. In addition, absorption also occurs at frequencies other than the Helmholtz frequency due to the vibration of the plate at additional eigenfrequencies. Both of these aspects of the technology advance the state-of-the-art in Helmholtz resonator design. Good agreement has been found between the modeling and experimental results. Near-perfect absorption was achieved experimentally, e.g., up to α = 0.995 below 1 kHz; in addition, given that the thickness of the technology can be a very small percentage of the acoustic wavelength that it is absorbing, deep sub-wavelength ratio absorbers can be designed, e.g., a ratio of up to 58 was achieved in this study with a 5 mm deep technology at 1.18 kHz.