Civil Engineering Reference
In-Depth Information
60
50
40
30
20
10
(a)
(b)
(c)
0
0.5
1
1.5
2
2.5
3
3.5
4
Frequency (kHz)
Figure 11.18
10 log
10
τ
at nor-
mal incidence of a glass wool bonded on to a plate. (b) Transmission loss of the plate.
(c) Transmission loss when the plate and the material are decoupled by an air gap.
(a) The predicted transmission loss coefficient
TL
=−
Table 11.9
The parameters used to predict the results of Figure 11.19.
Material
Thickness,
φ
σ
α
∞
ρ
1
E
ν
s
(N s/m
4
)
(kg/m
3
)
h
(mm)
(
µ
m)
(
µ
m)
(Pa)
6
.
6
×
10
3
2
.
93
×
10
5
Foam
25.4
0.98
1.03
200
380
11.2
0.2
0.06
10
10
Plate
1.6
2800
7
.
2
×
0.3
0.007
been chosen as 78
◦
. Prediction is compared in Figure 11.19 with measurement. Despite
the finite dimension of the material
(
0
.
8
×
0
.
8m
2
)
, the agreement between prediction
and measurement is good. Chapter 12 presents a correction for the size effects and its
experimental validation.
The transmission loss in the opposite direction (
TL
) has been verified to match the
transmission loss (
TL)
in the initial direction. The difference between the measured values
of
TL
and the transmission loss coefficient
TL
in the opposite direction is smaller than
2
·
5 db in the range (50 - 4000 Hz). The identity of
TL
and
TL
, can be proved by using
methods described in Allard (1993).
Several other transmission loss examples in both single wall and double wall config-
urations, together with diffuse field absorption examples accounting for size effects, will
be discussed in Chapter 12.
