The aim of the study was to analyse the effect of physical properties of natural fibre to the sound absorption coefficient. It was also aimed to study the relation of the physical properties of natural fibre to wider the frequency range and increase the sound absorption coefficient. There were two types of natural fibre will be studied such as kenaf fibre and rice straw fibre. The performance of sound absorption coefficient was measured using fabricated impedance tube according to ISO 10534-2. The physical properties of the natural fibre may affect the sound absorption coefficient either shifted to low frequency or shifted to high frequency range. All the physical properties that influence the sound absorption coefficient of natural fibre will be explained. The physical properties of natural fibre that will be studied were fibre thickness, fibre diameter and compressed fibre. Results have shown that the fibre thickness and diameter have a big effect to sound absorption coefficient. From the results, the utilization of the sound absorption coefficient can be achieved by choosing the suitable natural fibre according to its physical properties for a suitable application.

Fabrication of an impedance tube for measuring sound absorption coefficient is presented in this paper. Transfer-function method is chosen for the sound absorption analysis. The impedance tube is designed and fabricated in accordance with ISO 10534-2. The tube is made from brass with diameter of 114.3 mm and length of 1.42 m. It is designed for the frequency range 60 Hz to 1800Hz. Three microphone positions are installed to achieve the frequency range with a single tube. The theoretical background of transfer-function method between two microphones is discussed. Initially, impedance tube is characterized by the measurement without testing material in the tube. Micro-perforated panel (MPP) with 50 mm and 100 mm of cavity depth are used for measurement. The sound absorption coefficient measurement of the MPP is compared with theory and good agreement is achieved. Various problems related to design and construction is addressed and the optimal configuration is presented.