Building Acoustics

Sound transmission in buildings. Flanking transmission. 345

for direct transmission through the 50 mm concrete slab, which has a critical frequency
of about 400 Hz.

63 125 250 500 1000 2000 4000

Frequency (Hz)

0

10

20

30

40

50

60

70

80

Standa

rdized level diffe

rence

D

nT

(dB)

Concrete slab

Elastic layer

Primary floor

2 x 13 mm plasterboard

Figure 9.16 Standardized level difference between two rooms for music practice. Effect of flanking
transmission by way of a floating concrete slab.

9.3.1 Flanking sound reduction index

As an example on the calculation of the apparent sound reduction index, where the
flanking transmission is included, we shall assume that only flanking paths of the type
indicated by “Ff” on Figure 9.15 are contributing. To make use of the flanking reduction
index we shall have to express it by relevant and measurable quantities applied to the
flanking elements involved. We then have a situation as sketched in Figure 9.17, where
there is a direct transmission through the partition of area SS and reduction index Rd
together with a transmission path of the type mentioned above.
The apparent sound reduction index may then be written

d f

10 lg 10^101010.

R R

R

⎡ −−⎤

′=− ⋅ ⎢ + ⎥

⎢⎣ ⎥⎦

∑ (9.23)