Sains Malaysiana 40(6)(2011): 623–629

Kesan Lapisan Berliang dan Nisbah Keluasan Plat Berlubang Terhadap Ciri Akustik Serabut Sabut Kelapa Sebagai Bahan Penyerap Bunyi

(Effect of Porous Layer Backing and Perforation Ratio of Perforated Plate on Acoustic Characteristics of Coconut Fibre as a Sound Absorbent)

Zulkarnain*, Rozli Zulkifli & Mohd Jailani Mohd Nor

Jabatan Kejuruteraan Mekanik dan Bahan, Fakulti Kejuruteraan dan Alam Bina

Universiti Kebangsaan Malaysia, 43600, UKM Bangi, Selangor. D. E, Malaysia

Diserahkan: 10 Disember 2009 / Diterima: 2 September 2010

ABSTRAK

Penyelidikan ini dilakukan untuk mengkaji ciri akustik serabut sabut kelapa yang berpotensi digunakan sebagai bahan penyerap bunyi. Untuk meningkatkan ciri akustik serabut sabut kelapa pada frekuensi rendah, lapisan berliang digunakan di bahagian depan atau belakang bertujuan untuk meningkatkan nilai galangan permukaan. Bahan selanjutnya dilapisi dengan plat berlubang dengan nisbah keluasan yang berbeza. Sampel diuji mengikut piawaian antarabangsa ASTM E 1050-98 untuk menentukan pekali penyerapan bunyi. Daripada hasil uji kaji, plat 1 mm berlubang yang diperbuat daripada kepingan aluminium yang melapisi serabut sabut kelapa, didapati bahawa nilai maksimum pekali penyerapan bunyi berada pada frekuensi antara 2750 Hz hingga 2825 Hz iaitu dengan nilai 0.97. Nilai nisbah keluasan plat berlubang memberikan pengaruh penurunan pekali penyerapan bunyi pada frekuensi tinggi. Penurunan nilai pekali penyerapan bunyi terjadi apabila plat berlubang mempunyai nilai nisbah keluasan di bawah 0.22. Akan tetapi, penggunaan plat berlubang boleh meningkatkan prestasi penyerapan bunyi serabut sabut kelapa pada frekuensi rendah. Kesepakatan yang baik diperoleh daripada keputusan uji kaji dan analisis dengan pendekatan rangkaian elektrik setara yang digunakan untuk menghitung nilai pekali penyerapan bunyi. Ini menunjukkan bahawa pendekatan rangkaian elektrik setara boleh digunakan untuk merancang dan mengoptimumkan ciri akustik serabut sabut sebagai bahan penyerap bunyi.

Kata kunci: Lapisan berliang; plat berlubang; pekali penyerapan bunyi

ABSTRACT

This research was conducted to study the acoustic characteristics of coconut coir fiber which has high potential to be used as a sound absorbing material. To increase the acoustic performance of coconut coir fiber at low frequency, porous layer was installed in front or behind with the aims to increase the value of surface impedance. The perforated plate with a different ratio of perforation was used as a backing plate for the coconut coir fiber. Samples were tested according to international standard ASTM E 1050-98 for measurement of sound absorption coefficients. A 1 mm perforated plate made of aluminium backing with coconut coir fiber, showed the sound absorption coefficient with frequency between 2750 Hz and 2825 Hz with a maximum peak value of 0.97. The value perforation ratio of perforated plate could reduced the sound absorption coefficients at high frequency. The decrease in the coefficient in sound absorption occurred when the perforation ratio of perforated plates reached below 0.22. However, the use of perforated plates can increase the acoustics performance of coconut coir fiber at lower frequencies. Good agreement was obtained from the experimental results and analysis using the equivalent electrical circuit approach used to calculate the noise absorption coefficient. This shows that the equivalent electrical circuit approach can be used to design and optimize the acoustic characteristics of coir fiber as a sound absorbent.

Keywords: noise absorption coefficient; perforated plate; porous layer

RUJUKAN

Ballagh, K.O. 1996. Acoustical properties of wool. Applied Acoustics 48(2): 101-120.

Cox, T.J. & D’Antonio, P. 2004. Acoustic absorbers and diffusers theory, design and application. London: Spon Press.

Davern, W.A. 1977. Perforated facings backed with porous material as sound absorber – an experimental study. Applied Acoustics 10: 85-112.

Delany, M.E. & Bazley, E.N. 1970. Acoustical properties of fibrous absorbent materials. Applied Acoustics 3(2): 105-116.

Ersoy, S. & Kucuk, H. 2009 Investigation of industrial tea-leaf-fiber waste material for its sound absorption properties. Applied Acoustics 70: 215-220.

Hong, Z., Bo, L., Guangsu, H., & Jia, H. 2007. A novel composite sound absorber with recycled rubber particles. Journal of Sound and Vibration 304: 400-406.

Jinkyo, L., George, W. & Swenson, J. 1992. Compact sound absorbers for low frequencies. Noise Control Engineering Journal 38:109-117

Khedari, J., Charoenvai, S. & Hirunlabh, J. 2003. New insulating particleboards from durian peel and coconut coir. Building and Environment 38: 435-441.

Khedari, J., Nankongnab, N., Hirunlab, J. & Teekasap, S. 2004. New low-cost insulation particleboards from mixture of durian peel and coconut coir. Building and Environment 39: 59-65.

Lee, F.-C. & Chen, W.-H. 2001. Acoustic transmission analysis of multi-layer absorbers. Journal of Sound and Vibration 4: 621-634.

Maekawa, Z. & Lord, P. 1994. Environmental and architectural acoustics. London: E & FN Spon.

Munjal, M.L. 1987. Acoustics of Ducts and Mufflers., New York: John Wiley and Sons; Bah. 2.

Natarajan, V.D. 2000. Penilaian penyerapan akustik bahan tempatan menggunakan kaedah tiub galangan. Tesis Sarjana. Universiti Kebangsaan Malaysia.

Wassilieff, C. 1996. Sound absorption of wood-based materials. Applied Acoustics 48: 339-356.

Yang, H.S., Kim, D.J. & Kim, H.J. 2003. Rice straw-wood particle composite for sound absorbing wooden construction materials. Bioresource Technology 86: 117-121.

Zent, A. & Long, J.T. 2007. Automotive Sound Absorbing Material Survey Results. SAE international.

Zulkifli, R., Mohd Nor, M.J., Ismail, A.R., Nuawi, M.Z. & Mat Tahir, M.F. 2008. Acoustic properties of multi-layer coir fibres sound absorption panel. Journal of Applied Sciences 8: 3709-3714

*Pengarang untuk surat-menyurat; email: nain_sae@yahoo.co.id