Comportamento acústico de materiais absorvedores em multicamadas

Abstract

Nowadays problems that causes a lack of sound adjusment in enclousures has been a constant concern. The confortless caused by noise in enclousures can be minimized through the sound absorption capacity of the lining materials. In this research, the main acoustic properties of multilayer materials were experimentally determinedthrough the impedance tube. The matrix transfer method, acocording to the theoretical methods Delany-Bazley and Allard-Champoux, was implemented in Matlab software. In this context, the formulation of the theoretical model was used for the combinations of materials in which the experimental tests were performed, in order to compare the results. The materials used in this research were: polyurethane foam, polystyrene foam, cork and coconut fiber. 64 tests were performed using the impedance tube according to the International Standard ASTM E 1050-98 to measure the acoustic properties. The analysis and interpretation of experimental results has enabled to diagnose that in overall values for all frequency bands, foams have better performance, coconut fiber results sometimes are close to the foams ones and cork has the worst performance as an absorbing material. Tests made on systemscomposed by multilayer have identified the goals of the increase of thickness and the importance the importance of the variation of the acoustics properties according to the positioning of each material in the system. The theoretical model of Delany- Bazley did not represent the performances of the polyethylene foam and cork, representative values are shown for systems composed by two or three layers, expecially relating to the used material and positioning of the samples. The Allard-Champoux method shows results similar to Delany-Bazley for most systems it has been applied.