Enhancement of coir fiber normal incidence sound absorption coefficient

Mohammad Hosseini Fouladi, Mohd. Jailani Mohd Nor, Md Ayub, Masomeh Ghassem

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Coir fiber from coconut husk is an important agricultural waste in Malaysia. The porous structure of fiber makes it an eligible material for acoustical absorption. In previous studies at Universiti Kebangsaan Malaysia, single layer coir fiber showed low acoustical absorption in medium and low frequencies; e.g. absorption coefficient of a 20 mm industrial prepared coir fiber sample was below 0.3 for frequencies less than 1.5 kHz. Current research was initiated to improve the shortcoming by mixing industrial prepared coir fiber with air gap layers. Analyzes were based on two approaches, namely; DelanyBazley with acoustic transmission analysis (ATA) and Allard elastic model with transfer matrix analysis. Experimental measurements were conducted in impedance tube to validate the analytical results. Outcomes described that DelanyBazley-ATA technique was an approximate solution showing overall absorption path without giving any accurate information about the peaks and resonances. Allard method took the elasticity of material into account and transfer matrices were able to characterize the whole structure as a combination of single layers. Results were close to experimental values and predicted the path and resonances very well. Further analyzes were conducted by Allard method and derived that having a fiber layer backed by an air gap was better than leaving the same gap in between that layer. The explanation was that, in the first arrangement, the sound field impacted a solid layer with higher thickness and followed a longer transmission path which caused a higher acoustical absorption. Furthermore, it was noticed that a reasonable thickness of backing air gap improved the overall sound absorption. Increase in the gap thickness produced more peaks and moved them to lower frequencies which caused better absorption in low frequencies. The cause of this phenomenon was increase in impedance of the panel due to rise in the air-gap thickness. This moved the acoustical resonances to lower frequencies and improved the sound absorption in this frequency span. Finally, it was concluded that other acoustic absorption techniques such as adding perforated plate may be combined with coir fiber-air gap structure to improve the low frequency acoustic absorption coefficient without any need to highly increase the air gap thickness.

Original languageEnglish
Article number1250003
JournalJournal of Computational Acoustics
Volume20
Issue number1
DOIs
Publication statusPublished - Mar 2012

Fingerprint

Absorption Coefficient
sound transmission
Incidence
absorptivity
Absorption
Enhancement
incidence
Acoustic waves
Fiber
fibers
Fibers
augmentation
Low Frequency
Air
Acoustics
low frequencies
air
Malaysia
acoustics
Transfer Matrix

Keywords

  • Acoustic absorption coefficient
  • Acoustic transmission analysis (ATA)
  • Allard elastic model
  • Coir fiber
  • DelanyBazley
  • Porous material

ASJC Scopus subject areas

  • Applied Mathematics
  • Acoustics and Ultrasonics

Cite this

Enhancement of coir fiber normal incidence sound absorption coefficient. / Hosseini Fouladi, Mohammad; Mohd Nor, Mohd. Jailani; Ayub, Md; Ghassem, Masomeh.

In: Journal of Computational Acoustics, Vol. 20, No. 1, 1250003, 03.2012.

Research output: Contribution to journalArticle

Hosseini Fouladi, Mohammad ; Mohd Nor, Mohd. Jailani ; Ayub, Md ; Ghassem, Masomeh. / Enhancement of coir fiber normal incidence sound absorption coefficient. In: Journal of Computational Acoustics. 2012 ; Vol. 20, No. 1.
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KW - Porous material

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