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

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 structureOpen 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

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 2004.

Membrane absorbers

Membrane absorbers - application

Resonance absorbers – Helmholtz absorber

Resonance absorbers – perforated panels

Small holes shallow depth

Large holes shallow depthSmall holes big depth

Large holes big depth

Resonance absorbers – perforated panels

Resonance absorbers – perforated panels; effect of the open area

Perforated panels – applications

Perforated panels – applications

Perforated panels – applications

Which type of absorber?

Which type of absorber?

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

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

Questions?