Building Acoustics

Multilayer elements 305

()

()()

1

2

c^22

dil c

(^2222)
211

1 2 1

where.

21

6

K E

fK

h

hh

X

πXU

U

⎡⎤

⎢⎥ −

==⎢⎥

⎢⎥⎛⎞ −+

⎜⎟+

⎢⎥⎣⎦⎝⎠

21 X

(8.39)

63 125 250 500 1000 2000 4000

Frequency (Hz)

0

10

20

30

40

50

60

70

80

Sound

reduction index (dB)

Measured R'

Pred. E=5.0 MPa

Pred. E=6.0 MPa

Mass law

Figure 8.24 Sound reduction index of sandwich panel of 13 mm plasterboards and 55 mm polyurethane core.
Predicted data using two different modulus of elasticity for the core. Measured data from Homb et al. (1983).

Table 8.2 Material data for sandwich panel in Figure 8.24.

E-modulus

(Mpa)

Density

(kg/m^3 )

Loss factor

Poisson’s

number

Face sheets, 13 mm

plasterboard

3200 800 0.05 0.30

Core, 55 mm polyurethane 5 − 6 50 0.05 0.35

Concerning the fit between predicted and measured results in the lower frequency
range, one should be reminded that the prediction applies to an infinite size panel, i.e. no
area effect is included. Furthermore, the panel area of 7.5 m^2 being used for the