Building Acoustics

Sound transmission in buildings. Flanking transmission. 327

1 10 100

Area ratio S 0 /S 1

0

5

10

15

20

R

- 0

R

tot

(

dB)

18

15

12

9

6

3

S 0

S 1

Figure 9.1 Calculation of the sound reduction index of a composite construction, e.g. a partition containing a
door or window. The parameter is R 0 – R 1 , the difference in the sound reduction indices.

9.2.1 Apertures in partitions, “sound leaks”

The results shown above may be used to estimate the influence of unintentional
weaknesses in a building element, e.g. a partition, examples being badly sealed cable
ducts or just building defects as slits or apertures. The problem is to find the effective
transmission factor or the sound reduction index of such apertures, sealed or not. If the
aperture is open one may, as a starting point, assume that the pertinent area has a
reduction index equal to zero. However, as we shall see, this is too rough a
simplification. Intuitively, one should expect that sound waves experience some
difficulties in passing through apertures where the transverse dimensions are less than the
wavelength. One should therefore expect such reduction indexes to be frequency
dependent. A greater problem associated with such apertures is that one will encounter
resonance phenomena that may in some frequency ranges give reduction indexes of the
order –5 to –10 dB.
Pioneering work for prediction tools in this field were performed by Wilson and
Soroka (1965) and Gomperts and Kihlman (1967), the latter pair of authors also made
comparison with full-scale measurements. These works are, however, limited to the
treatment of apertures as being open, i.e. there is no kind of filling materials or sealing,
an aspect taken up by Mechel (1986). Vigran (2004) extended the work on open
apertures by including apertures having a variable transverse shape (conical apertures
and wedge-shaped slits). The transmission aspects were, however, not the primary
concern of this work but the design of resonator absorbers using panels having these
types of perforation. The sound reduction index of an open aperture in a wall of