Why is static deflection the input rather than the mount's stiffness rating?

Because deflection is what the mount is actually doing under your machine, and stiffness is only what it was designed to do. A mount loaded well below its rating barely deflects and barely isolates; one loaded past its rating bottoms out and stops being a spring at all. Natural frequency follows from deflection alone, which is why the measurement matters more than the data sheet.

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 would. Above it, transmissibility falls below one and the mount begins to isolate. The value comes straight from the transmissibility equation, where the transmitted and applied forces are equal at a ratio of the square root of two.

My mounts are amplifying. Should I order stiffer ones?

No, and this is the most expensive mistake in vibration isolation. Stiffer mounts deflect less, which raises the natural frequency, which lowers the frequency ratio and pushes you further into amplification. You need softer mounts with more deflection, a heavier inertia base, or a change in running speed. Stiffness is the intuitive answer and the wrong one.

Why does the calculator ignore damping?

It fixes damping at 0.05, typical of elastomeric mounts, rather than asking for it. Above a ratio of about two, damping barely changes the ratio-based conclusion this page reaches, and an estimator cannot measure a damping ratio in the field. Asking for it would add a fifth input that looks like knowledge and is really a guess. Damping does matter at resonance, which is why this page refuses to treat a machine running near r = 1 as merely a low ratio and flags it separately.

What if my machine runs at several speeds?

Check the lowest one. Frequency ratio scales with speed, so the slowest running condition gives the smallest ratio and the worst isolation. A variable-speed drive that is comfortable at full speed can sit right on resonance at turndown, which is a common and confusing complaint pattern because the machine only misbehaves at part load.

Does a good ratio mean the vibration problem is solved?

It means the mounts are positioned correctly in frequency, which is necessary but not sufficient. This is a single-degree-of-freedom check: it does not cover rocking modes, floor flexibility, piping and conduit that bypass the mounts entirely, or structure-borne paths through the building. A machine on well-chosen mounts can still transmit vibration through a rigid conduit connection nobody thought about.

Acoustic, Noise, Vibration & NVH Products calculator

Isolator Resonance Frequency Calculator

Check whether the vibration isolators under a machine are actually isolating it or quietly making things worse. Enter the static deflection the mounts show under load, the machine's running speed, the harmonic order that drives the vibration, and the frequency separation you are designing for. The calculator converts deflection into the mount's natural frequency, converts speed and order into the forcing frequency, and reports the ratio between them along with the margin above the amplification limit. Everything about isolator performance follows from that ratio, and a mount chosen without checking it can transmit more force than no mount at all.

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.
Use it for checking mounts already under a machine that still shakes the floor, specifying deflection before ordering isolators for a new install, diagnosing why a stiffer mount made a vibration complaint worse, screening a variable-speed drive at its lowest running speed.
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 when the equipment sits on it. Measure it; do not take it from the catalogue rating.
Machine running speed: Operating speed of the rotating element that drives the vibration.
Harmonic order of concern: 1 for shaft imbalance, 2 for misalignment, blade or vane count for fans and pumps.
Target frequency ratio: The separation you want between the forcing frequency and the mount's natural frequency. Three is the usual design target; two is workable with little margin; anything under √2 amplifies.

How to use the result

Best suited to checking mounts already under a machine that still shakes the floor, specifying deflection before ordering isolators for a new install, diagnosing why a stiffer mount made a vibration complaint worse, screening a variable-speed drive at its lowest running speed.
One degree of freedom only: it says nothing about rocking, pitching or the other five rigid-body modes. Ignores floor flexibility, which can create a second resonance the mount cannot fix. Not a structural analysis and not a bearing-fault diagnostic. Says nothing about transmitted amplitude, only about the frequency relationship that governs it.

Common questions

Why is static deflection the input rather than the mount's stiffness rating? Because deflection is what the mount is actually doing under your machine, and stiffness is only what it was designed to do. A mount loaded well below its rating barely deflects and barely isolates; one loaded past its rating bottoms out and stops being a spring at all. Natural frequency follows from deflection alone, which is why the measurement matters more than the data sheet.
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 would. Above it, transmissibility falls below one and the mount begins to isolate. The value comes straight from the transmissibility equation, where the transmitted and applied forces are equal at a ratio of the square root of two.
My mounts are amplifying. Should I order stiffer ones? No, and this is the most expensive mistake in vibration isolation. Stiffer mounts deflect less, which raises the natural frequency, which lowers the frequency ratio and pushes you further into amplification. You need softer mounts with more deflection, a heavier inertia base, or a change in running speed. Stiffness is the intuitive answer and the wrong one.
Why does the calculator ignore damping? It fixes damping at 0.05, typical of elastomeric mounts, rather than asking for it. Above a ratio of about two, damping barely changes the ratio-based conclusion this page reaches, and an estimator cannot measure a damping ratio in the field. Asking for it would add a fifth input that looks like knowledge and is really a guess. Damping does matter at resonance, which is why this page refuses to treat a machine running near r = 1 as merely a low ratio and flags it separately.
What if my machine runs at several speeds? Check the lowest one. Frequency ratio scales with speed, so the slowest running condition gives the smallest ratio and the worst isolation. A variable-speed drive that is comfortable at full speed can sit right on resonance at turndown, which is a common and confusing complaint pattern because the machine only misbehaves at part load.

Last reviewed 2026-08-24.