This seems like a simple task with all the various wall and floor
designs available with tested Sound Transmission Coefficient (STC)
ratings. However, the complexity of this issue arises when these
wall and floor assemblies are also being required to maintain fire-
rated separations between occupancies within the building and the
STC rating and fire rating of these assemblies are compromised by
plumbing, electrical, and mechanical penetrations as well as joints
created between wall and floor assemblies. This is where passive
fire protection products known commonly as firestop products are
called upon to maintain the STC rating of the wall assembly as well
as maintain the fire rating of the assembly being penetrated.
How STC Ratings are Determined
For sound transmission testing in a laboratory, the sound is
transmitted from one room to another only through the separating
wall or floor specimen under test. In a building, however, there are
many paths for transmission of sound and associated structure-
borne vibration, as indicated in Figure 2.A. As a result, sound
isolation between adjacent rooms in a building is often much less
than would be expected from rated sound transmission performance
of the separating wall or floor assembly.
(Fig 6.1 Illustration of some typical paths for sound transmission)
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