Broadband noise control through a ducted opening

Abstract

Fresh air ventilation openings or windows are essential to most buildings but the openings allow considerable portions of noise to be transmitted from the outdoor into the indoor environment. This project studies relevant theoretical models through accurate numerical solutions, and seeks better designs to gain extra noise attenuation through the openings.

The spectral method of Chebyshev collocation and the corresponding technique of out-going wave boundary conditions, for both ducted and flanged opening, are developed as numerical tools and validated by analytical examples.

After establishing the numerical tools, two prototype problems are studied. The first is one in which there is no special sound attenuation device. The configuration includes aperture of negligible thickness, aperture of finite thickness and aperture of semi-infinite length. The characteristics of the noise transmission through aperture of finite thickness are investigated with examples of sonic boom and traffic noise. The second prototype problem is the sound attenuation performance of side-branch design of the ducted opening. Side-branch configurations including porous material, single micro-perforated panel, double-layer micro-perforated panels, parallel micro-perforated panels and parallel micro-perforated panels with connected cavity are investigated. They are tested individually with parameters optimized for each of two examples of noise sources. The sound attenuation performances compared using appropriate subjective ratings of the noise sources. It is found that the parallel micro-perforated panels give the best performance for the sonic boom and the double-layer micro-perforated panels serve as the best substitute for the porous material with traffic noise source. Results from experiment are also presented to validate some numerical results.