Analysis on multiple Perforated Plate sound absorber made of coir fiber

Abstract

Current studies are aiming to improve the sound absorption of coir fiber by implementing combinations of Perforated Plates (PPs) and air gaps. The Atalla and Sgrad model along with Johnson-Allard model and Acoustic Transmission Analysis (ATA) approach are used to estimate the absorption coefficient of the combination. Measurements are conducted in impedance tube to validate the analytical results. Outcomes show that the absorption coefficient of the panel is governed by the porosities of the implemented PPs. Reduction in the porosity of the face PP causes the incident sound to reflect back whereas higher porosity encourages the sound to enter and be absorbed gradually in the inner compartments. For the case of multilayer panels with two PPs, the best result is obtained when the inner PP has low porosity and is backed with an air gap. Absorption in high and low frequency bands are enhanced by having highly porous material and a thick layer of air gap in front of and behind the inner PP, respectively. This study shows that the high-frequency absorption is enhanced further in panels that include three PP layers. The study suggests fabricating panels containing two or three PPs with gradual reduction of porosity from the face PP to the inner ones, while the inner most PP has low porosity and is backed with air gap.