Customers sometimes ask us a simple question: “Can this isolator provide 90% vibration isolation?”

The percentage sounds straightforward, but it cannot be answered from the isolator model alone. Isolation efficiency changes with equipment mass, excitation frequency, isolator stiffness and damping.

In application reviews, we have seen customers choose a mount from load capacity first and check vibration frequency later. The mount may safely support the equipment but still operate too close to resonance to provide useful isolation.

That is why HOAN normally asks for equipment weight and vibration frequency together.

How Is Vibration Isolation Efficiency Calculated?

Isolation efficiency describes the reduction in vibration transmitted through an isolation system.

A commonly used expression is:

Isolation Efficiency (%) = (1 − T) × 100

where T is vibration transmissibility.

If:T = 0.2

then:Isolation Efficiency = 80%

In simple terms, the transmitted response represented by that transmissibility ratio is 20% of the input.

But this does not mean the isolator has a fixed “80% efficiency.” Change the excitation frequency or supported mass, and the result can change.

This is the first distinction we make when reviewing an isolation application.

Why Frequency Ratio Determines Isolation Efficiency

For a simplified vibration isolation system, the key relationship is the frequency ratio:

r = f / fn

where:

· f = excitation frequency

· fn = natural frequency of the isolated system

The behavior changes considerably as this ratio increases.

This relationship is much more useful than asking for an isolation percentage without specifying frequency.

A Practical Example: Shipboard Electrical Equipment

Consider a shipboard electrical cabinet exposed to a dominant vibration around 30 Hz.

If the mounted system has a natural frequency of 15 Hz:

r = 30 / 15 = 2

The system is above the theoretical isolation threshold, but the frequency ratio is still relatively low.

Now consider an isolator that reduces the system natural frequency to 7.5 Hz:

r = 30 / 7.5 = 4

The higher ratio can provide substantially better vibration attenuation.

On paper, the second option appears better. In an actual installation, however, the softer mounting may allow more cabinet movement.

Cable clearance, connector movement, mounting stability and available travel now become part of the decision.

This is a situation we pay close attention to during isolator selection: a lower natural frequency may improve theoretical isolation, but the resulting movement still has to fit the equipment installation.

30 Hz Excitation

Option A: fn = 15 Hz → r = 2
Option B: fn = 7.5 Hz → r = 4

Underneath:

Higher frequency ratio → lower transmissibility, but check available travel.

How Stiffness and Equipment Mass Affect Natural Frequency

For a simplified system:

fn = (1 / 2π) √(k / m)

where k is stiffness and m is supported mass.

This explains why selecting an isolator only by maximum load can cause problems.

Two mounts may both support the same equipment weight while having very different stiffness characteristics. Their resulting natural frequencies—and therefore their isolation performance—can be different.

Reducing stiffness generally lowers natural frequency and improves isolation when the operating frequency is sufficiently high.

The cost is additional deflection.

For equipment with limited clearance, simply choosing the softest available mount is rarely a good engineering approach.

How Damping Affects Vibration Isolation

Damping matters most around resonance because it controls the response peak.

More damping, however, does not automatically produce better isolation at frequencies well above resonance.

For nonlinear designs such as wire rope isolators and friction damping isolators, actual load-deflection and vibration test data can be more useful than treating the mount as an ideal linear spring.

This is particularly relevant when equipment experiences variable speed, startup and shutdown rather than operating continuously at one fixed frequency.

Why Operating Frequency Range Matters

A generator, compressor or fan rarely behaves as a perfect single-frequency vibration source.

Suppose a compressor has significant vibration around 25 Hz and 50 Hz. Evaluating the isolator only at 50 Hz may show excellent isolation while overlooking a potential response closer to resonance at the lower frequency.

For variable-speed equipment, startup and shutdown can also sweep through the system natural frequency.

In these applications, we prefer to review the operating frequency range or vibration spectrum, not just one frequency value.

That usually tells us more about the real isolation requirement than a requested percentage such as “90% efficiency.”

Is 90% Isolation Always Better Than 80%?

Not if achieving it creates too much movement.

A softer isolation system may improve attenuation, but excessive deflection can lead to cable strain, connector movement, contact with surrounding structures or poor equipment stability.

The engineering target is therefore not the highest possible percentage.

It is to reduce transmitted vibration to an acceptable level without exceeding the available displacement or compromising the installation.

This balance is especially important for cabinets, communication equipment, optical systems and other installations where movement space is limited.

What Information Does HOAN Need?

For a preliminary isolation review, equipment weight and vibration frequency are the best starting points. We also look at the number and position of mounts, installation orientation, available movement and center of gravity when it is known.

If test data is available, send the original vibration spectrum rather than converting it into a single frequency.

A mounting drawing is also useful. It often reveals load-distribution and clearance issues that cannot be identified from equipment weight alone.

For applications that also have a separate mechanical shock requirement, shock performance should be evaluated independently from vibration isolation efficiency.

FAQ

Is 90% vibration isolation good?

It can be, but the percentage only has meaning when the operating frequency and measurement conditions are known. The required attenuation depends on how sensitive the protected equipment is.

When does vibration isolation begin?

For a simplified linear system, transmissibility drops below 1 when the excitation-to-natural-frequency ratio exceeds approximately √2.

Does a softer vibration isolator provide better isolation?

It can lower the system natural frequency and improve isolation at higher frequency ratios, but it also increases deflection. The available travel must be checked before selecting a softer mount.