This paper describes the analysis on the sound absorption characteristics of perforated membrane absorber. This study aimed to investigate the effect of perforation sizes and percentage of perforation areas on the membrane sound absorption characteristic. The effects of physical and material properties of the membranes such as thickness, Young's modulus and density were also investigated. The characteristics of the perforated membrane absorber were measured experimentally in terms of Sound Absorption Coefficient, α and Noise Reduction Coefficient, NRC by utilizing impedance tube method in compliance with ISO 10534-2 standard. The results showed that the peak value of absorption coefficient is determined by the density and thickness of the membranes. The perforation sizes also have a significant effect on the sound absorption coefficient and frequency range width. Optimal perforation size enhances the sound absorption performance of the membrane. Overall, the perforated membranes give better sound absorption coefficient and wider frequency range compared to the unperforated membranes

The three-rattle angklung is a traditional musical instrument made of bamboo. The objective of this research is to observe the unique sound characteristics of the three-rattle angklung. The sound characteristics data can be used for defining digital sound of angklung to be played in a digital synthesizer. One set of angklung from the big size C 5 to the small size C 6 is recorded and analyzed in terms of the frequency contents. The sound characteristics of angklung are represented by four dominant frequency contents and the corresponding relative amplitudes of each rattle bamboo tube. This paper also introduces an equation model to predict the sound produced by the bamboo of the three-rattle angklung. This research reveals that bamboo rattles 2 and 3 produce the fundamental note, and bamboo rattle 1 generates a higher octave with the same note. Each bamboo rattle produces fundamental frequency note, its harmonics, and overtones. It is also found that three-rattle angklung can produce an accurate frequency almost in every note.

Motorised cutter has been used in palm oil plantations and becomes an added value to improve its productivity during harvest. However, frequent use of the machine can cause damages to human hand arm and fingers caused by vibration. This paper presents a study on the hand arm vibration produced by a motorised cutter with pole 3 metres length. The objective of this study is to assess the safety of the machine to the users. The measurements involve taking vibration measurement at both grip of point 1 and point 2. These experiments involve two skilled users and two unskilled users which run in real palm oil plantation. The measurements are made according to ISO 5349,evaluation of hand arm was assessed from different angle of cutting, vibration values at both grip point and the standard limit exposure action A(8). Skilled user shows vibration exposed to less than 2.5m/s2 indicating safe condition of using the machine. The unskilled user shows vibration exposed to more than 2.5m/s2 indicating caution condition should be taken when handling the machine. From the data obtained, it is suggested to provide guidelines or training for any users so that less vibration transmission can be transferred to user when using this machine.