1. Sound absorption Eng.Ivaylo Hristev

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

3. Normal sound absorption coefficient

4. Diffuse sound absorption coefficient

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

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

8. Porous absorbers – typical examples

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

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

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

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

13. Porous absorbers – applications

15. Membrane absorbers – construction Membrane Porous absorber Air cavity Rigid backing

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

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

18. Membrane absorbers - application

19. Resonance absorbers – Helmholtz absorber

20. Resonance absorbers – perforated panels

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

22. Resonance absorbers – perforated panels; effect of the open area

23. Perforated panels – applications

26. Which type of absorber?

28. 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 α p according to EN ISO 354. Then the values are compared to a standardized curve. Weighted absorption coefficient

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

30. Questions?