Civil Engineering Reference
In-Depth Information
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Measurements without facing
Prediction without facing
Measurements with facing
Prediction with facing
0.1
0
0
0.5
1
1.5
2
2.5
3
3.5
4
Frequncy (Hz)
Figure 11.9
The absorption coefficient of the foam with and without facing. The param-
eters for the foam and the facing are give in Table 11.3. Measurements reproduced from
Rebillard
et al
. (1992).
Blanket (1)
Screen (2)
Foam (3)
Foam (4)
Figure 11.10
A layered material comprising a blanket (1), a screen (2) and two foams
(3) and (4). The material is bonded onto a rigid impervious wall.
with and without the screen are presented in Figure 11.12. The predicted increase in the
absorption due to the screen is important at low frequencies as in the case of the first
material.
The last example consists of a moderately thin resistive screen inserted between a
foam and a felt. The properties of the materials are in Table 11.5. The normal incidence
absorption of the system is compared with simulations in Figure 11.13 in the configu-
ration where the foam is bonded onto a rigid wall. Both the foams and the felt were
