Enhancing noise control in a cavity using Helmholtz resonators

Abstract

In this paper it is shown that there is a decrease in sound levels, not only when a resonator is tuned exactly to a cavity mode, but also when it is tuned to a frequency slightly different from the natural frequency of the chosen cavity mode. The finite element (FE) method is used for numerical modelling of the coupled Helmholtz resonator-cavity system. To validate the FE model prediction, a boundary element (BE) analysis is performed by specifying an impedance boundary condition on the element where the resonator is mounted. This impedance has been calculated, from a BE model of the resonator alone, using a plane wave excitation, over a range of frequencies around the cavity mode of interest. Numerical experiments have been performed in a cavity with two close modes (155 and 173 Hz) and it is observed that when a resonator is tuned to a frequency slightly lower than the first cavity mode, the performance of the resonator is much better than when it is tuned exactly to the first cavity mode or tuned to a slightly higher frequency. A detailed parametric study has been carried out and guidelines for tuning resonators for superior noise control is proposed. © 2013 Acoustical Society of America.