Why is static deflection the input, not stiffness?

Deflection is what the mount is doing under your machine; stiffness is only what it was designed to do. A mount loaded well below its rating barely deflects and barely isolates. Natural frequency follows from deflection alone.

What is special about a ratio of √2?

It is the crossover. Below it transmissibility exceeds one and the mount transmits more force than a rigid connection. Above it the mount isolates. The value comes from the transmissibility equation, not from a rule of thumb.

My mounts are amplifying. Should I order stiffer ones?

No. Stiffer mounts deflect less, which raises the natural frequency, lowers the ratio and pushes you further into amplification. You need softer mounts, a heavier base, or a different running speed.

What if my machine runs at several speeds?

Check the lowest one. Ratio scales with speed, so the slowest condition gives the smallest ratio and the worst isolation. A drive comfortable at full speed can sit on resonance at turndown.

Acoustic, Noise, Vibration & NVH Products calculator

Isolator Resonance Frequency Calculator

Check whether the isolators under a machine are isolating it or making things worse. Enter deflection, running speed, harmonic order and target ratio; the page returns the natural frequency and the frequency ratio.

What this calculator does

Check whether a mount's natural frequency is safely below the machine's forcing frequency, from the mount's measured static deflection.

Formula used

Disturbing frequency = machine speed × harmonic order ÷ 60
Mount natural frequency = 3.13 ÷ √(static deflection in inches)
Frequency ratio = disturbing frequency ÷ natural frequency
Isolation begins above a ratio of √2 ≈ 1.41; below it the mount amplifies
Deflection for the target ratio = (3.13 ÷ (disturbing frequency ÷ target ratio))²

Inputs explained

Static Deflection Under Load: How far the mount actually sinks under the equipment.
Machine Running Speed: Operating speed of the rotating element that drives the vibration.
Harmonic Order of Concern: 1 for imbalance, 2 for misalignment, blade count for fans.
Target Frequency Ratio: Separation wanted between forcing frequency and natural frequency.

How to use the result

Best suited to checking mounts already under a shaking machine, specifying deflection before ordering isolators, diagnosing why a stiffer mount made vibration worse.
One degree of freedom only: it says nothing about rocking or pitching modes. Ignores floor flexibility, which can create a second resonance the mount cannot fix. Says nothing about transmitted amplitude, only the frequency relationship that governs it.

Common questions

Why is static deflection the input, not stiffness? Deflection is what the mount is doing under your machine; stiffness is only what it was designed to do. A mount loaded well below its rating barely deflects and barely isolates. Natural frequency follows from deflection alone.
What is special about a ratio of √2? It is the crossover. Below it transmissibility exceeds one and the mount transmits more force than a rigid connection. Above it the mount isolates. The value comes from the transmissibility equation, not from a rule of thumb.
My mounts are amplifying. Should I order stiffer ones? No. Stiffer mounts deflect less, which raises the natural frequency, lowers the ratio and pushes you further into amplification. You need softer mounts, a heavier base, or a different running speed.
What if my machine runs at several speeds? Check the lowest one. Ratio scales with speed, so the slowest condition gives the smallest ratio and the worst isolation. A drive comfortable at full speed can sit on resonance at turndown.

Last reviewed 2026-10-01.