Building Acoustics

356 Building acoustics

other curves show the result when the floor is improved by adding a floating floor as well
as a freely suspended ceiling; see the inserted sketch. Without the elastic layers, we may,
by taking the actual vibration level difference into account, easily estimate that these
improvements, even when reducing the transmission through the floor to zero, will only
add around 5–6 dB to our R ́. In this case, the transmission between the rooms takes
place solely by way of the flanking walls. Adding the elastic layers, however, we get, as
expected from the measured vibration level differences, a greatly improved insulation.

63 125 250 500 1000 2000 4000

Frequency (Hz)

0

10

20

30

40

50

60

70

80

Sound

reduction index (dB)

Total

Lightweight wall

Brick walls ex/lining

Concrete floor

Figure 9.24 Apparent sound reduction index of a lightweight double leaf wall with flanking brick walls and
concrete floors. Other curves indicate reduction index based on radiated power from the pertinent elements in
the receiving room. Predictions after Bastian®.

Finally, as an example on the use of the complete model given in EN 12354 Part 1,
we shall calculate R ́ for a conventional lightweight double leaf wall; two 13 mm
plasterboard layers with a cavity of 75 mm thickness filled with mineral wool. The area
of the wall is 15 m^2 , partitioning two rooms with dimensions 8 x 5 x 3 metres (length x
width x height) and 6 x 5 x 3 metres, respectively. The floors are 180 mm thick concrete,
whereas the flanking walls are ½ stone brick, plastered on both sides.
Calculations are performed using Bastian®, giving results as shown in Figure 9.24.
The lowest curve gives the reduction index based on the total transmitted power to the
receiving room by way of all transmission paths, giving a weighted apparent sound
transmission index R ́w of 44.8 dB. The other curves shows the predicted reduction index