This paper discusses the acoustic performance of absorbers constructed using hollow tube structures. Tubes made of polypropylene plastic utilising waste from lollipop sticks were used in this study. The absorption coefficient was tested using the impedance tube method for three different structure arrangements, namely parallel (axial) or perpendicular (transverse and crossed transverse) directions subject to sound incidents on the length of the tubes. The effect of the length or layer thickness of the structures, air gap behind the sample and also introduction of fabric were investigated. The results revealed that the tubes in transverse and crossed transverse arrangements showed greater absorption coefficients compared to the axial arrangement. For a layer thickness of 2 cm and 3 cm, the absorption coefficients were almost unity and the average absorption coefficients were 0.6 above peak frequency. The presence of air gaps shifts the absorption peak to a lower frequency. Enhancements on absorption coefficients in axial arrangements were obtained by introducing fabric covering the front and/or back of the sample.

Synthetic acoustic materials are known for their poisonous chemical substance to the environment and also the particles which are harmful to human health. Research is now directed towards finding an alternative acoustic absorber made from natural materials. This paper presents the utilization of bamboo, a natural material having hollow structure to act as sound absorber. In an impedance tube test, the hollow path is arranged to face the sound incidence. The result reveals that bamboo having length of 2 cm has average absorption coefficient of 0.95 at frequency above 3 kHz. Performance at lower frequencies can be controlled by adding the air gap behind the system. Introduction of microholes along the body shows no significant effect to increase the sound absorption.

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