Vibration Theory

Vibration Isolation reduces the level of vibration transmitted to or from a machine, building or structure from another source.

The degree of isolation achieved depends on the ratio:2: The level of isolator damping C/Cc.

Referring to the diagram 3.07, the degree of isolation is given as Transmissibility (i.e. amount of vibration transmitted at a specific frequency ƒe as a fraction of the disturbing vibration at the same frequency ƒe).

Transmissibility
> 1 = Increased transmitted vibration
= 1 = No vibration isolation
< 1 = Vibration isolationTransmissibility T can be read from diagram 3.2 or calculated as follows:
If no damping present in isolators i.e. C/Cc = 0

Damping Factorfrequency ratio R fe/fn

C/Cc 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
0.05 20 66 80 87 91 93 94 95
0.10 19 64 79 85 89 91 93 94
0.15 17 62 76 83 87 90 91 93
0.20 16 59 74 81 85 87 89 91
0.30 12 52 67 75 80 83 85 87
Percentage Isolation Efficiency

Ktd = Sum of Isolator Dynamic Spring Constants
(K1+K2+K3…) N/m
M = Supported system mass kg.

For natural rubber and coil spring isolators static and dynamic spring constants are the same.