Building Acoustics

Sound transmission in buildings. Flanking transmission. 355

by the absorption length a. As a first approximation, the standard suggests setting these
equal to the areas S, which gives

S

0

10 lg ,

2

ij

ij ij

ij

RR S

RK

ll

+ ⎡ ⎤

≈++⋅⎢ ⎥

⎢⎣ ⎥⎦

(9.47)

where l 0 is a reference length equal to 1.0 metre. In case of additional linings on the
flanking elements, the resulting improvements ΔRi and/or ΔRj has to be added to the
right-hand side of the equation. Before showing some predicted results based on this
model, we shall return to the experiments which attempt to improve the vibration
reduction index by applying elastic layers. The reason is that these measured results
clearly illustrate the fine line between the dimensioning of the partition versus the
flanking elements.

Figure 9.23 Apparent sound reduction indexes by applying elastic layers in the joints. The dashed curve applies
to the primary construction; 150 mm lightweight concrete without elastic layers. The other curves apply to the
case of a primary floor with additional floating floor and suspended ceiling. After Huse (1972).

63 125 250 500 1000 2000 4000

Frequency (Hz)

10

20

30

40

50

60

70

80

A

pparent sound reduction index,

R

' (dB)

Basic construction

Without layers

Layer, uppper side

Layer, lower side

Layer, both sides

In Figure 9.23 the results from a total of five separate measurements of the apparent
sound reduction index are shown, which apply to the floor slab in the “building” having
the measured velocity level difference depicted in Figure 9.21. The lowest curve
(dashed) applies to the primary constructions without any elastic layers in the joints. The