Performance of Multi-Orifice Resonator on Higher Order Modes of an Acoustic Cavity

This paper emphasizes on lower frequency noise reduction in an acoustic cavity. The acoustic cavity is a pentagonal prism with irregular dimensions and non-parallel walls. First six modes of the acoustic cavity is considered for the analysis. Numerical analysis for tuning and coupling the resonator to the cavity is carried out using Finite Element Modeling software ANSYS. The experimental validation is performed on fabricated models by exciting both the systems using a dodecahedral loudspeaker with a white noise source. Multi-orifice rectangular resonators are tuned to each cavity mode frequency by varying their geometrical parameters. Throughout the analysis the resonator cavity volume and the overall surface area of the orifice is held constant. Harmonic analysis is carried out to determine the overall sound pressure levels (SPL) of the uncoupled and coupled resonator-cavity systems. The difference in SPL from the both gives the amount of noise reduced. The analysis shows that the total amount of noise reduction over a band is more when a resonator is coupled to higher order modes than when coupled to only the first mode of the cavity. The amount of noise reduction was about 8 dB when coupled to 110 mode. Few results are validated using experiments.