Civil Engineering Reference
In-Depth Information
wall area
S
we may just multiply by
n
to arrive at the total radiated power. We have
assumed that the radiation factor of the basic wall is approximately equal to 1.0, hence
2
Wc
=
ρ
u
S
.
(8.14)
1
0
0
1
−
1
⎡
⎤
4
2
2,B
u
W
W
W
⎛⎞
f
⎢
⎥
i
i
i
0
=
=
+ ⋅
n
σ
.
(8.15)
⎜⎟
B
WW W nW Wf
+
+ ⋅Δ
⎢
2
⎥
u
⎝⎠
2,P
2,B
2,P
2,B
1
⎣
1
⎦
u
2,B
u
1
W
i
W
1
W
i
W
2,P
W
2,B
a)
b)
Figure 8.8
Heavy basic wall with additional acoustical lining.
Inserting this equation into Equation
(8.11)
, we get
RR
=+Δ
⎡
R
,
1
⎤
4
2
2,B
u
(8.16)
⎛⎞
f
⎢
⎥
0
where
Δ=− ⋅
R
10 lg
+⋅
n
σ
.
⎜⎟
B
⎢
f
2
1
⎥
u
⎝⎠
⎣
⎦
The quantity Δ
R
is thereby the improvement of the reduction index due to the additional
lining. To calculate this improvement we shall need an expression for the radiation factor
σ
B
. However, we have shown in Chapter 6 (section 6.4.2.1) that the radiated power from
a bending wave near field on a plate driven at a point and along a line, respectively, is
given by
