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Sound absorption
Eng.Ivaylo Hristev
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Contents
1.Normal and diffuse sound absorption coefficient.
2. Sound absorber types:
•Porous absorbers
•Membrane absorbers
•Resonance absorbers
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Normal sound absorption coefficient
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Diffuse sound absorption coefficient
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Diffuse sound absorption coefficient
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Porous absorbers – open cell structure
Closed cell structure
Open cell structure
Source Cremmer&Muller 1978
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Closed look of real world materials
Porous absorbers – open cell structure
Closed cell structureOpen cell structure
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Porous absorbers – typical examples
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Porous absorbers – thickness
Diffuse absorption coefficient of polyurethane foam with the same density and different thickness; source Cox&D’Antonio 2004
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Simulated diffuse sound absorption coefficient of mineral wool with density 50kg/cub.m. and various thickness.
Porous absorbers – thickness
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Porous absorbers – air cavity thickness
Simulated diffuse sound absorption coefficient of mineral wool with density 50kg/cub.m. and various air cavity thickness.
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Porous absorbers covered with thin layer
Diffuse sound absorption coefficient of mineral wool with density 60 kg/cub.m. covered with 0.1mm polyethylene.
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Porous absorbers – applications
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Porous absorbers – applications
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Membrane absorbers – construction
Membrane
Porous absorber
Air cavity
Rigid backing
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Membrane absorbers
Diffuse sound absorption coefficient of a membrane absorber with various membrane thicknesses with and without rockwool.
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Simulated and measured sound absorption coefficient of a membrane absorber; source Cox&D’Antonio 2004.
Membrane absorbers
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Membrane absorbers - application
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Resonance absorbers – Helmholtz absorber
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Resonance absorbers – perforated panels
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Small holes shallow depth
Large holes shallow depthSmall holes big depth
Large holes big depth
Resonance absorbers – perforated panels
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Resonance absorbers – perforated panels; effect of the open area
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Perforated panels – applications
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Perforated panels – applications
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Perforated panels – applications
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Which type of absorber?
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Which type of absorber?
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Weighted sound absorption coefficient αw is calculated according to EN ISO 11654. Measured sound absorption coefficient αs is averaged in 1/3 octave band frequencies as αp according to EN ISO 354. Then the values are compared to a standardized curve.
Weighted absorption coefficient
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The same standard EN ISO 11654 classifies the sound absorbers into different classes. ISO 354 absorption coefficient αp is compared in which region fits.
Sound absorption classes
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Questions?