Wide-Band Micro-Perforated Panel Sound Absorbers And Its Application In Open-Plan Offices

Modern open-plan offices have high density of staff,where the sounds produced by work activities and communications are a ubiquitous noise problem to the staffs.The work efficiency and the sound privacy of the staffs will be hardly destroyed if lack of effective treatments.One control method is to add appropriate sound absorbing materials on the ceiling and other indoor surfaces.Conventional fiber and porous absorption materials may cause some environmental issues such as the accumulation of dust and bacteria,so that it is hard for them to adapt the needs of green open-plan offices.Micro-perforated panel(MPP)absorber may be a good alternative since it is a new type of dust free and water proof sound absorbing material.But the the existing MPP absorbers commonly have narrow absorption bandwidth,which constraints the mass applications of them.In order to solve this problem,the feasibility of broadening the absorption bandwidth of the single-layer MPP absorber with finite-sized cavity is firstly investigated in this paper.The absorption characteristics of this type of MPP absorber are numerically analyzed through a finite element model,and the ways and mechanisms of broadening the absorption bandwidth of it are also discussed.The results indicate that the absorption bandwidth of the single-layer MPP absorbers can obtain one octave broadening when the width to depth ratio of the finite-sized rectangular cavity is effectively designed.The mechanism is the grazing eigen-modes can be induced in the rectangular cavity by the oblique incidence sounds,which result in absorption peaks in the frequencies that higher than the resonance frequency of the normal incidence sound,therefore broaden the absorption bandwidth.To further broaden the absorption bandwidth of the MPP absorber,and to satisfy the higher demand of sound absorption and noise reduction of the open-plan offices,a compound MPP absorber that has an array of parallel arranged sub-cavities with different depths is investigated in this paper,the depth sequence of sub-cavities is designed according to the quadratic residue diffuser(QRD).An analytical method for predicting the absorption performance of this type of MPP absorber is proposed;an acoustic finite element model is built to validate the analytical method,and to analyze the absorption characteristics of this type of MPP absorber,a full scale sample of this type of MPP absorber is made and the normal incidence absorption coefficient of it is measured.The numerical and experimental results indicate that the analytical method presented in this paper is accurate;this type of MPP absorber can obtain customizable absorption peaks and positions and thus possesses the potential to be wide-band absorber that covering the full band of voice and speech,when the MPP properties and the depth sequence of the sub-cavities are effectively designed.Finally,this paper combines the above studies and the spectrum characteristics of the speech noise,which is the main noise of the open-plan offices,designs and discusses the applications of two types of wide-band MPP absorbing ceilings in open-plan offices.An acoustic model of a typical open-plan office is built based on ODEON software;the control effects of the wide-band MPP absorbing ceilings on office noise are numerically analyzed,the spatial decay rate of speech and sound transmission index are also discussed.The results indicate that,in comparison with conventional mineral wool absorbing ceiling,the two types of wide-band MPP absorbing ceilings have better control effects on speech noise because of the specially designed absorption spectra of them.