Sound%20absorption

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
5
Diffuse sound absorption coefficient
6
Porous absorbers open cell structure
Closed cell structure
Open cell structure
Source CremmerMuller 1978
7
Porous absorbers open cell structure
Closed cell structure
Open cell structure
Closed look of real world materials
8
Porous absorbers typical examples
9
Porous absorbers thickness
Diffuse absorption coefficient of polyurethane
foam with the same density and different
thickness source CoxDAntonio 2004
10
Porous absorbers thickness
Simulated diffuse sound absorption coefficient of
mineral wool with density 50kg/cub.m. and various
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
14
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
Membrane absorbers
Simulated and measured sound absorption
coefficient of a membrane absorber source
CoxDAntonio 2004.
18
Membrane absorbers - application
19
Resonance absorbers Helmholtz absorber
20
Resonance absorbers perforated panels
21
Resonance absorbers perforated panels
Small holes shallow depth
Large holes shallow depth
Small holes big depth
Large holes big depth
22
Resonance absorbers perforated panels effect
of the open area
23
Perforated panels applications
24
Perforated panels applications
25
Perforated panels applications
26
Which type of absorber?
27
Which type of absorber?
28
Weighted absorption coefficient

• Weighted sound absorption coefficient aw is
  calculated according to EN ISO 11654. Measured
  sound absorption coefficient as is averaged in
  1/3 octave band frequencies as ap according to EN
  ISO 354. Then the values are compared to a
  standardized curve.

29
Sound absorption classes

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

30
Questions?