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TECHNICAL PAPERS

Investigating the Effects of Fibrous Material Compression on the Acoustical Behavior of Absorption and Barrier Materials

[+] Author and Article Information
A. R. Ohadi

Mechanical Engineering Department,  Amirkabir University of Technology, Hafez Avenue, Tehran 15914, Irana̱ṟohadi@aut.ac.ir

M. Moghaddami

Automotive Engineering Department,  Iran University of Science and Technology, Tehran 16844, Iran

J. Vib. Acoust 129(2), 133-140 (Oct 20, 2006) (8 pages) doi:10.1115/1.2424975 History: Received August 07, 2005; Revised October 20, 2006

This paper discusses the effects of compression on acoustical performance of fibrous materials. A finite element model is used to predict the absorption coefficient and transmission loss of absorbing and barrier materials. This model is developed based on the Galerkin method and includes the equation of wave propagation in rigid frame porous material. The compression of fibrous material is entered to the model with relations that explain modifications of physical properties used in the wave equation. Acoustical behavior of absorption and barrier materials with and without compression is studied. It is shown that compression of the material leads to reduction of the transmission loss of the barrier materials and absorption coefficient of absorbing materials. In this regard, “thickness reduction” and “variations of physical parameters” due to compression are investigated.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Schematic of impedance tube apparatus; (b) geometry of the problem. A layer of fibrous material at the end of a semi-infinite wave guide with rigid walls. Excitation by a planar normal incident wave.

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Figure 2

Convergence of calculated result due to element number for a 50‐mm-thickness polyester layer excited with 1000Hz plane wave

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Figure 3

Absorption coefficient curve of polyester layer versus frequency—comparison with experimental results of Ref. 11

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Figure 4

Absorption coefficient curve of compressed polyester layer (n=1.61) versus frequency—comparison with experimental results of Ref. 11

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Figure 5

Absorption coefficient curves versus excitation frequency for various thicknesses of the polyester layer

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Figure 6

Effect of compression rate on the absorption coefficient curve of the polyester layer

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Figure 7

Effect of compression rate on the noise reduction of a polyester layer with initial thickness of 50mm—compared with uncompressed layer with initial thickness equal to final thickness of the compressed layer

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Figure 8

Noise reduction of polyester layer with various initial thicknesses after compressing to 50mm—compared with uncompressed layer with the same initial thickness

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Figure 9

Transmission loss curves for various thicknesses of the rigid glass wool layer

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Figure 10

Effect of compression rate on the transmission loss curve of the rigid glass wool layer

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Figure 11

Effect of compression rate on the transmission noise reduction of the rigid glass wool layer with initial thickness of 50mm—compared with uncompressed layer with initial thickness equal to final thickness of the compressed layer

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Figure 12

Transmission noise reduction of the rigid glass wool layer with various initial thicknesses after compressing to 50mm—compared with uncompressed layer with the same initial thickness

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