Sound absorption coefficient assessment of sisal, coconut husk and sugar cane fibers for low frequencies based on three different methods

Sound absorbing materials for noise control are distinguished due to their high efficiency in sound absorption. However, many of these materials are of synthetic origin and cannot be disposed of as solid waste in nature or incinerated by industry, because they are very polluting. Natural fibers can be an important alternative to replace these materials in noise control area. The present work aims to evaluate the sound absorption coefficient of three natural fibers: sisal, coconut husk and sugar cane with two empirical and one experimental method. Ten samples of each material with 20, 30 and 40 mm in thickness were evaluated. The empirical models applied in the analyzes were published by Delany and Bazley in 1970 and Allard and Champoux in 1992. The Allard and Champoux method is a simplified approach to minimize Delany and Bazley inconsistencies at low frequencies. The predictions of the empirical methods were compared with an experimental analysis using the transfer function method based on the ASTM 1050-12 standard. Finally, an inverse methodology was presented to optimize the coefficients of the Delany and Bazley model to better represent the studied fibers. (C) 2019 Elsevier Ltd. All rights reserved.