“Transmissibility Ratio (TR)” is the term commonly used and a plot of the variation of the TR is shown in Fig. 9.4.1. It is observed that when the system is designed such that  < (1.414), the TR actually exceeds unity. In order that the TR is sufficiently small, it is desirable to keep the frequency ratio about 5 i.e., the natural frequency of the system must be about 5 times lower than the operating frequency. However, if the springs are made very soft so as to keep the natural frequency low, it could result in excessive static deflection (under the weight of the machine itself). Thus the mountings need to be carefully designed.
Often the mounting system is made up of rubber mounts (e.g., engine mounts in a car), or cork pads apart from the conventional helical coil springs, shock absorbers etc.It is also observed that as
 , damping actually increases the T.R. Thus it would appear necessary to have as low damping as possible. However, to reach an operating point corresponding to (i.e.,
 ) one needs to pass through
 , resonance. To limit resonance
amplitudes. We need to have sufficient damping in the system.
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