Sound absorption Eng Ivaylo Hristev Contents 1 Normal

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

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

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

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

Porous absorbers – air cavity thickness Simulated diffuse sound absorption coefficient of mineral wool with density 50 kg/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. 1 mm 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.

Membrane absorbers Simulated and measured sound absorption coefficient of a membrane absorber; source Cox&D’Antonio 2004.

Membrane absorbers - application

Resonance absorbers – Helmholtz absorber

Resonance absorbers – perforated panels

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

Resonance absorbers – perforated panels; effect of the open area

Perforated panels – applications

Which type of absorber?

Weighted absorption coefficient 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.

Sound absorption classes The same standard EN ISO 11654 classifies the sound absorbers into different classes. ISO 354 absorption coefficient αp is compared in which region fits.

Questions?