Mohd Jailani Mohd Nor

Utilizing Malaysian Natural Fibers as Sound Absorber

Previous researchers [1, 2, 3, 4] successfully produced sound absorption panels using agricultural wastes. These panels play important role both in noise absorption and heat insulation preserving the comfort of indoor living spaces. Yang et al. [4] produced rice straw-wood particle composite boards. They found that the sound absorption coefficient of these boards is higher than other wood-based materials in the 500-8000 Hz frequency range. Reason was the low specific gravity of composite boards having high amount of porosity compared to wood-based materials [4]. Another study by Davern [5] aimed at producing airspace layers and examined the influence of porosity on the acoustic properties of materials. He found that the porosity of the perforated plate and the density of the porous material would significantly affect the acoustic impedance and sound absorption coefficient of the panel, in which case, the frequency band near the resonance frequency achieved high acoustic absorption. In addition to Davern’s study, Lee and Chen [6] reported that the acoustic absorption of multi-layer materials is better with a perforated plate backed with airspaces. Other usages of natural fibres are in reduction of sound propagation in automotive interior spaces, or to improve the control of outdoor noise propagation [7, 8]. Recent studies show that researchers are focusing on coir fibre and oil palm fibre in replacing synthetic-based fibres for sound absorption applications simply due to their abundance in tropical countries such as Malaysia.

Application of acoustic emission technique to observer the engine oil's viscosity

This paper presents an investigation of the capability of the acoustic emission (AE) technique in the processes of monitoring and detecting the variation of engine oils viscosity via in-situ operation. The investigations were conducted on an 8.5-hp single cylinder of four strokes with a water cooling engine. One single grade engine oils condition has been put to the test; namely, SAE 40 VI 96. The oil condition in the engine was successfully monitored based on the AE signatures generated by the interaction between the piston surface and the layer of the oil during the time that the engine was in operation. The generated AE signatures were captured using an AE wide band transducer that was bonded outside the engine block and located at the lower part of the bottom dead centre (BDC). The captured waveform signatures were then analysed using the MATLAB software. The results of the experimental works show that the statistical analysis parameters including the root-mean-square (rms), maximum amplitude and AE energy values are capable of distinguishing the variant of the viscosity. The AE technique can assist the owner of the engine in determining the engine oils condition before replacing it.

Assessment of road traffic noise indices in urban residential areas of Klang Valley, Malaysia

Traffic noise has been recognized as a serious threat to the quality of life in most industrialised nations. Klang valley is rapidly emerging as industrialized and urbanized city and has started facing severe noise pollution problems. Urban noise quality assessment is studied in three residential areas; Desa Tun Razak, Kinrara Court and Taman Sentul Utama. Noise pollution indices of L10, L50, L90, Lmax and Lmin as well as equivalent continuous noise level (Leq) were measured for all dwellings. Noise indices results illustrate that Desa Tun Razak recorded the highest values of noise levels among three studied sites. Results also indicate that the highest Leq of 75.7u2005dB(A) was observed in Desa Tun Razak followed by 74.3u2005dB(A) in Kinrara Court, and 72.1u2005dB(A) in Taman Sentul Utama. The noise assessment study clearly reveals the alarming condition of noise pollution in residential areas of Klang Valley as the noise level measured exceeded permissible limit by WHO and Malaysia Guidelines.

Acoustic Benefits of Ecofriendly Spent Tea Leaves Filled Porous Material

This paper demonstrates the feasibility of spent tea leaf (STL) fiber as an eco-friendly sound absorbing material. STL fiber is a by-product which was extracted from tea plant. STL are rich in polyphenols (tannins) which cause high resistance to fungal and termites, and high resistance to fire. In addition, STL are hollow and cellular in nature and thus perform well as acoustic and thermal insulators. Three different grades of STL were studied and the acoustic property was analyzed in terms of sound absorption coefficient and transmission loss. Experimental measurements of sound absorption coefficient in impedance tube are conducted. It was found that finest STL fiber grade exhibits better acoustic performance among others. Furthermore, the effect of latex binder on the acoustic property of STL fiber was also analyzed. Results suggest that the types of binder such as polyurethane and latex influenced the acoustic performance of STL fiber.

Enhancement of acoustical performance of hollow tube sound absorber

This paper presents acoustical performance of hollow structures utilizing the recycled lollipop sticks as acoustic absorbers. The hollow cross section of the structures is arranged facing the sound incidence. The effects of different length of the sticks and air gap on the acoustical performance are studied. The absorption coefficient was measured using impedance tube method. Here it is found that improvement on the sound absorption performance is achieved by introducing natural kapok fiber inserted into the void between the hollow structures. Results reveal that by inserting the kapok fibers, both the absorption bandwidth and the absorption coefficient increase. For test sample backed by a rigid surface, best performance of sound absorption is obtained for fibers inserted at the front and back sides of the absorber. And for the case of test sample with air gap, this is achieved for fibers introduced only at the back side of the absorber.

Efficacy study of embedded binaural beats in gamma brainwave synchronization

Electrical impulses and chemical activities in human brain generate brain waves at frequency domains ranging between 0.5 Hz and 100 Hz that characterize different mental states. The states of attention and focus can be traced to areas within the prefrontal cortex (PFC) of the brain at gamma brainwave frequencies of about 40 Hz and above. The cerebral brain cells can be synchronized to a desired frequency by externally stimulating the cells using acoustical means such as binaural beats (BB). Exposure to pure beats can be annoying and stressful to the listener. BB signals embedded in a background audio could provide better listening comfort to the subject. This paper presents a study on the efficacy of embedded BB in gamma-domain brainwave synchronization. Electroencephalograph signals indicative of the auditory evoked potential (AEP) on test subjects due to resonance of the PFC with the induced aural stimuli are measured. It is observed that the BB signals masked in an audio background give AEP values that are on average 92% similar to that generated by pure BB. The results indicate that the embedded BB has an effect comparable to pure BB on the AEP measured at selected PFC locations at the 40 Hz gamma frequency.

Preliminary Study on Bamboo as Sound Absorber

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.

Improvement of Fire Retardant Property of Natural Fiber

Excessive exposure to noise is harmful for human health. Noise-induced hearing loss is one prevalent disorder resulted from above case. One root solution that converts the unnecessary sound waves to dissipated heat energy is acoustic absorption panel. Previous studies had looked upon potential sound-absorbing resources corresponding to natural fiber. However, several characteristics of these biodegradable supplies such as stiffness, anti-fungus and flammability are still yet to be improved. Hence, this research was undertaken to enhance the fire retardant performance of coir fiber for the production of high quality yet low cost acoustic absorption panel. Three types of additives, borax, Di-Ammonium Phosphate (DAP), and urea were investigated to perform chemical treatment for coir fiber. Experimental measurements were executed to validate the results by referring standard of ASTM E6902 (Standard Test Method for Combustible Properties of Treated Wood) by using the Fire-Tube Apparatus. Final results showed that DAP-treated fiber has the lowest percentage loss in mass of 6.67% compared to that of borax and urea-treated fiber with values of 7.60% and 9.48% respectively. This outcome clarified that DAP-treated fiber possesses higher self-extinguishing ability. Further evaluations in term of economic values, degree of hazards against health, flammability as well as reactivity supported that DAP is the best choice since its potency was ahead of the other two chemicals.

Replacement of synthetic acoustic absorbers with natural fibers

The goal of this study was to implement Malaysian natural fibers as sound absorbers in acoustic panel. Four natural fibers, namely; coir, corn, sugar cane and grass were chosen and their acoustic absorption properties examined. Samples were tested in impedance tube complying with the standard ISO 10534-2. Increase in the thickness improved the absorption coefficient and samples of coir, corn and grass with 2 cm thickness absorbed more than 70% of normal incident sound at approximately f>1500 Hz. Comparison with synthetic materials having the same thickness showed that these fibers have better absorption coefficient throughout the frequency spectrum. Fiber-glass was an exception and still considered one of the best materials for acoustic insulation however it has adverse effects on human health and its utilization is no longer recommended. The results supported the viability of natural fibers as alternative to conventional synthetic absorbers in acoustic panels.Copyright