Acoustical coupling and radiation control of open cavity using an array of Helmholtz resonators

This paper presents the theoretical and experimental investigations on the suppression of noise radiation from a point source inside an open cavity with three-dimensional configuration using several Helmholtz resonators (HRs). A theoretical model is established based on the modal superposition method to study the acoustical coupling between a rectangular open cavity and multiples HRs. Additionally, a baffled open cavity is considered to couple acoustically with a semi-infinite exterior field using the acoustic coupled mode theory. The theoretical model facilitates the understanding of the mechanism of the peak formation in the sound pressure level spectrum at the receiving points outside the cavity and the noise suppression mechanism by the HRs. In addition, the relationship between those sound peaks, and that of the resonances of the enclosed cavity and open cavity are investigated to have a good design of HR. The location and internal resistance of HR are optimised to obtain a desirable attenuation of noise radiation from the open cavity. Subsequently, experiments are performed to validate the proposed model and examine the feasibility of the HR in suppressing noise radiation from the open cavity. The noise reduction around the sound peak indicates that both the single and multiple sound peaks of the open cavity can be controlled successfully by adopting HRs. The practical significance of this study is to provide a new insight into sound reduction in an open acoustical system through suppressing the resonant response by resonators.