Noise control in a small enclosure using T-shaped acoustic resonators

This paper presents a passive method to control the broadband noise inside a small enclosure using multiple, optimally located, T-shaped acoustic resonators. The resonators consist of two mutually perpendicular tubes: one short and one long. The significance of the T-shaped acoustic resonator is its large aspect ratio, which makes it possible to be integrated into host structures to reduce the space requirement in implementation. When the resonator is introduced into a noisy enclosure, the re-radiation from its aperture, excited by the primary source, interacts with the existing sound to effectively attenuate the noise level inside the enclosure. A general model is developed, representing the acoustic interaction between the enclosure and multiple resonators, which is used to evaluate the acoustic performance of the resonators. Based on the understanding of the coupling between resonators and enclosure modes, both targeted and nontargeted, a sequential design method is proposed to determine the optimal location of the resonator. Numerical simulations are carried out to demonstrate the implementation procedures of noise control in several resonance peaks of a right parallepiped enclosure. Experiments are also conducted to validate the theory and the design method. The agreement between the theoretical and experimental results shows that, with the help of the presented theory, noise levels within a relatively broad frequency band in an enclosure can be successfully attenuated using optimally located acoustic resonators.