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Transmissibility and isolation

Transmissibility shows what fraction of a force or vibration is transmitted through a spring-damper mount (isolator). Below $r = \sqrt2$ the force is actually amplified, while vibration isolation only works well once the frequency ratio is well above $\sqrt2$ .

TR = \dfrac{1}{|1-r^2|}

transmissibility, undamped

r = \omega/\omega_n

frequency ratio

Symbols

$TR$	transmissibility
$r$	frequency ratio
$\omega$	excitation frequency	rad/s

Example

$r = 3$ :

$TR = 1/|1-9| = 0.125$ – only 12.5% of the force is transmitted.

Soft mounts (low

\omega_n

) give a higher

r

at the operating frequency and thus better isolation.

Practise forced vibrations and isolation for free →

← Resonance and amplification · Unbalance force →

Part of Machine Dynamics and Vibrations: Forced vibrations and isolation.