Abstract
Absorbent materials are fibrous or porous and must have the property of being good acoustic dissipaters. The noise reduction process occurs due to transformation of a part of the sound energy into heat. This process occurs when a sound wave propagates through pores or irregular arrangement of fibers. Sound propagation causes multiple reflections and friction of the air present in the absorbent medium transforming sound energy into heat. The acoustic surface treatment with absorbent material are widely used to reduce the reverberation in enclosed spaces or to increase the sound transmission loss of acoustic panels. In addition, these materials can also be applied to acoustic filters with the purpose to increase their efficiencies. The sound absorption depends on the excitation frequency of the sound and it is more effective at high frequencies. Natural fibers such as coconut coir fiber have a high potential to be used as sound absorbing material. Natural fibers are agriculture waste, manufacturing this fiber is a natural product, therefore an economic and interesting option. This work compares the sound absorption coefficient of a thin coconut coir fiber panel in relation to a composite panel made of fiberglass and expanded polyurethane foam used in the automotive industry. The evaluation of sound absorption coefficient was carried out with the impedance tube technique.
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