Building Acoustics

296 Building acoustics

undulating sound reduction curve but followed the general trend of the measured data,
although the model was strictly two-dimensional.
Another approach to such analytical modelling, also taking advantage of the
periodicity of the studs, is offered by Brunskog (2005). The effect of the studs on the
sound field in the cavity is also taken into account but again the cavity was empty. The
agreement between measured and predicted results is quite good.

63 125 250 500 1000 2000 4000

Frequency (Hz)

0

10

20

30

40

50

60

70

80

Sound

reduction index (dB)

Davy, steel

Meas. steel

Davy, wood

Sharp, wood

Meas. wood

Figure 8.16 Sound reduction index of double leaf partition of 13 mm plasterboards on common wooden and
steel studs, respectively. Measured data from Homb et al. (1983). Predictions according to Sharp (1978) and
Davy (1991).

8.2.2.3 Heavy (massive) double walls

We have in the preceding section dealt with lightweight double leaf constructions where
the leaves were connected by studs of various types. In the cases where the leaves are
mounted on a separate system of studs there normally exists structural connections along
the edges of the wall. In many cases such couplings are “weak” in the sense that the
adjoining constructions have a much larger mass and stiffness, and the coupling is of
little consequence unless a common, stiff frame is used.
This situation is quite distinct from the one experienced in double constructions
involving brick or concrete, even including so-called lightweight concrete. The coupling
along the boundary may completely determine the achieved result. In extreme cases there
may be no improvements by using a double construction as compared with a single one.