Civil Engineering Reference
In-Depth Information
τ
=
πτ
(0).
(9.5)
diffuse
This implies that the sound reduction index for diffuse incidence will be approximately 5
dB smaller than for normal incidence.
m
1
φ
Γ,
Z
c
ϕ
m
2
2a
d
Figure 9.3
Cylindrical aperture in a wall filled with a porous material and sealed by mass layers.
50
40
30
20
Empty
Min. wool
Tape
Min. wool + tape
10
0
-10
100
1000
50
200
500
2000
5000
Figure 9.4
Sound reduction index at normal incidence. Cylindrical aperture of radius 10 mm in a wall of
thickness 100 mm. Mineral wool of flow resistivity 5 kPa⋅s/m
2
. Sealing tape of mass/area 100 g/m
2
.
Frequency (Hz)
We shall illustrate the use of Equation
(9.4)
by again using a cylindrical aperture of
radius 10 mm in a wall of thickness 100 mm (see
Figure 9.4
). The curve giving the result
for a an open or empty aperture is the same as shown in
Figure 9.2
, however, now using
