Sound absorption Eng.Ivaylo Hristev. Contents 1.Normal and diffuse sound absorption coefficient. 2. Sound absorber types: Porous absorbers Membrane absorbers.

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Presentation transcript:

Sound absorption Eng.Ivaylo Hristev

Contents 1.Normal and diffuse sound absorption coefficient. 2. Sound absorber types: Porous absorbers Membrane absorbers Resonance absorbers

Normal sound absorption coefficient

Diffuse sound absorption coefficient

Porous absorbers – open cell structure Closed cell structure Open cell structure Source Cremmer&Muller 1978

Closed look of real world materials Porous absorbers – open cell structure Closed cell structure Open cell structure

Porous absorbers – typical examples

Porous absorbers – thickness Diffuse absorption coefficient of polyurethane foam with the same density and different thickness; source Cox&D’Antonio 2004

Simulated diffuse sound absorption coefficient of mineral wool with density 50kg/cub.m. and various thickness. Porous absorbers – thickness

Porous absorbers – air cavity thickness Simulated diffuse sound absorption coefficient of mineral wool with density 50kg/cub.m. and various air cavity thickness.

Porous absorbers covered with thin layer Diffuse sound absorption coefficient of mineral wool with density 60 kg/cub.m. covered with 0.1mm polyethylene.

Porous absorbers – applications

Membrane absorbers – construction Membrane Porous absorber Air cavity Rigid backing

Membrane absorbers Diffuse sound absorption coefficient of a membrane absorber with various membrane thicknesses with and without rockwool.

Simulated and measured sound absorption coefficient of a membrane absorber; source Cox&D’Antonio Membrane absorbers

Membrane absorbers - application

Resonance absorbers – Helmholtz absorber

Resonance absorbers – perforated panels

Small holes shallow depth Large holes shallow depth Small holes big depth Large holes big depth Resonance absorbers – perforated panels

Resonance absorbers – perforated panels; effect of the open area

Perforated panels – applications

Which type of absorber?

Weighted sound absorption coefficient αw is calculated according to EN ISO Measured sound absorption coefficient αs is averaged in 1/3 octave band frequencies as α p according to EN ISO 354. Then the values are compared to a standardized curve. Weighted absorption coefficient

The same standard EN ISO classifies the sound absorbers into different classes. ISO 354 absorption coefficient α p is compared in which region fits. Sound absorption classes

Questions?

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