On Helmholtz resonators with tapered necks

The acoustical properties of Helmholtz resonators with necks having cross-section dimensions decreasing away from the entry of the resonator cavities are investigated experimentally and theoretically in the present study. Results show that significant improvement of the sound absorption capacity of the resonators can be obtained by introducing such neck tapering. Such improvement is enhanced when the tapered length is increased. The present derived theory predicts the resonance frequency of the tapered neck resonator within engineering tolerance and the accuracy is again improved as the tapered length increases.