Building Acoustics

Multilayer elements 285

uniformly distributed elastic springs as well as a more accurate model taking the discrete
placing of the studs into account by treating the wall as a periodic structure, see for
example Lee and Kim (2002), who treated single panels with stiffeners and Wang et al.
(2005), who extended this model to double leaf constructions. The “smeared” type of
model follows the approach used for floating floors (see section 8.4.1) and in practice,
there certainly are double wall constructions where the layers are connected in this
manner, e.g. by a continuous elastic layer such as stiff mineral wool. A model for such
cases has been presented by Kropp and Rebillard (1999).

63 125 250 500 1000 2000 4000 8000

Frequency (Hz)

0

10

20

30

40

50

60

70

80

Sound

reduction index (dB)

Meas. w/abs.

Pred. w/abs.

Meas. ex/abs.

Pred. ex/abs.

Figure 8.7 Sound reduction index of lightweight double leaf constructions without structural connections.
Measured and predicted results by Brekke (1979), using a frame absorber (w/abs.). Measured and predicted
results by Crocker et al. (1971), using an empty cavity (ex/abs).

By lightweight double leaf partitions of plasterboard, chipboard etc. mounted on
common studs, forces or moments transmitted through these studs normally are the
determining factor in the frequency range above the double wall resonance. The
development of studs having reduced stiffness is an important task as specially profiled
steel studs have shown to give large improvements. Certainly, there will normally always
be direct structural connections along the perimeter of a partition (edge coupling) but
these are not equally important for lightweight constructions as for heavy, massive
systems.