constrained layer damping treatments, such as illustrated in figure 10.6, consist of
a layer of viscoelastic material sandwiched between the structure and a layer of steel
or aluminium. As a rule of thumb, the viscoelastic layer is about 1/3 as thick as the
surface to be damped and for vibrating structures less than 1.5 mm thick the
constraining outer layer should be the same thickness. For vibrating structures of
thickness between 1.5 and 3mm, the constraining layer should be 1.5mm thick and
for vibrating structures with a thickness of greater than 3mm, the constraining layer
should be 3mm thick. Sometimes these rules of thumb produce a structure which is
effectively damped in a particular frequency range which may not be the frequency
range in which the noise radiation is a problem. In this case it may be necessary to
fine tune the layer thicknesses, either experimentally or theoretically (see Cremer et.
al., 1988).