Civil Engineering Reference
In-Depth Information
flanking transmission. These models will, however, become quite complicated for
multiple layer wall constructions and complex junctions. In such cases, modelling by
SEA may be appropriate. A hint on how such problems could be treated will be outlined
using the example shown in
Figure 7.4
, where the rooms are modelled as subsystems 1
and 3. The separating wall constitutes subsystem 2, and we shall include only two
flanking walls in the model, one wall in each room being subsystems 4 and 5.
4
4
5
5
1
1
2
2
3
3
Non-resonant coupling
Non-resonant coupling
Figure 7.5
SEA model for the situation shown in
Figure 7.4.
One very important aspect, which should be borne in mind, is that the whole
concept of SEA presupposes resonant systems and resonant transmission. The non-
resonant part of the sound transmission through the wall at frequencies below the critical
frequency, the part calculated by the mass law, must therefore be included in a separate
way. In
Figure 7.5,
this part of the transmission is shown by the direct connection
between subsystems 1 and 3, which are the rooms.
From the simple example above, comprising two subsystems, we have already
some of the expressions needed to fill into the matrix Equation
(7.8)
to solve for the
sound transmission problem. However, it is easily seen that the key terms will be the
coupling loss factors, which may be hard to estimate. Determining these factors by
experiments may in practice be the only solution. (Set up the complete matrix equation
for the system given in
Figure 7.5
and try to pick out the most important components.)
Finally, we shall present an example on measured and predicted sound pressure
level difference between two rooms caused by the different transmission paths using the
above model. The results are laboratory measurement results from Building Research
Establishment, UK, reproduced in the topic by Craik (1996). The laboratory is
constructed to measure the influence of flanking transmission, in the specific case the
partition wall, subsystem 2, is concrete block cavity wall. The external flanking walls,
subsystems 4 and 5 are lightweight block and brick cavity walls.
Figure 7.6
shows both the overall measured and predicted sound pressure level
difference together with the predicted dominant transmission paths. The symbols
included in parenthesis are taken from the calculation models in the standard EN 12354
Part 1. The symbols D and F refer to the partition and flanking wall, respectively, seen
from the sending room and the small letters, d and f, correspondingly refer to the ones
seen from the receiving room. Further treatment of these models is postponed until
Chapter 9.
