Theory and applications of quarter-wave resonators: A prelude to their use for attenuating noise entering buildings through ventilation openings

This paper concerns the use of quarter-wave resonators to attenuate noise. Qualitative and quantitative derivations of the relationship between cavity length and wavelength of sound to be attenuated are presented. The mechanism by which resonators can be used to attenuate noise is developed in terms of the optimum scattering and absorption conditions at resonance. The aim is not to present detailed mathematical expressions for the design of quarter-wave resonators, rather to illustrate the design principles involved for practical applications and to demonstrate that the advantage of such resonators is their simplicity of design. Recent applications of quarter-wave resonators ave described including their use to attenuate fan noise and in conjunction with conventional barriers to reduce transportation noise. A new application is proposed involving the use of such resonators outside building ventilation openings to attenuate noise entering buildings. Unlike other applications discussed, resonators of different lengths are used to achieve attenuation over a wide frequency range rather than at an isolated, discrete frequency. (C) 1997 Elsevier Science Ltd.