A Study of Helmholtz Resonators on Broadband Noise Control and Their Potential Application on Ventilation

Noise abatement and ventilation control are two important aspects in improving the indoor environmental comfort in buildings. The aims of this thesis were to achieve a better understanding of the broadband noise control and ventilation effects of Helmholtz resonators.;To obtain a boarder noise attenuation band, combing several resonators is a possible way. This thesis reported a theoretical study of sound propagation in a one-dimensional duct with identical side-branch resonators mounted periodically. The results predicted by the theory fit well with the computer simulation using a three-dimensional finite element method and the experimental results. This study indicated that the wave coupling in this periodic system resulted in the distribution of the frequency band into the stop- and the pass-bands. The long-term significance is that periodic resonators may more effectively control noise in ducts by broadening the bandwidth they attenuate.;This thesis also considered the disorder in the periodic duct-resonator system. It was found that the analysis of the disorder in the geometries of resonators with periodic distance being kept unchanged provides a useful way for the design of such a system to achieve a relatively wide noise attenuation band and to track some narrow noise peaks within it.;Apart from their extensive application on noise control, Helmholtz resonators were found to have the effect on ventilation. This thesis presented the results of a theoretical investigation of the airflow through the neck into the cavity of a side-branched Helmholtz resonator. It was found that the motion of the airflow in the opening may result in an air jet formed in the resonator that provided the fresh air from the ventilation duct. This ventilation method can be considered as "AC" ventilation with the electrical analogy, which is far less understood than the traditional ventilation method.;It is hoped that the present study can provide a stepping stone for investigation of both the acoustic and ventilation performance of Helmholtz resonators, and seeking their potential application in improving the indoor environmental comfort in buildings.