How do I select the right vibration mount?

Select vibration mounts based on the machine mass, operating frequency, and desired isolation percentage. The mount must have a natural frequency well below the disturbing frequency — typically fn ≤ fd/√2 for any isolation, and fn ≤ fd/3 for 90% isolation.

What isolation percentage should I target?

For general machinery, 80-90% isolation is typical. For sensitive equipment near precision instruments, 95%+ is desired. The higher the isolation percentage, the softer (lower stiffness) the mounts must be, which increases static deflection.

What is the relationship between static deflection and natural frequency?

Natural frequency fn = (1/2π)√(g/δst), where δst is static deflection and g is gravitational acceleration. A static deflection of ~25 mm gives fn ≈ 3.1 Hz. Softer mounts (more deflection) give lower natural frequency and better isolation.

How many mounts should I use?

Typically 4 mounts for rectangular machines (one per corner). Use 3 for triangular arrangements, 6 for large machines or when load distribution is uneven. Each mount carries a fraction of the total load.

What happens if mounts are too soft or too stiff?

Too stiff: insufficient isolation, vibration transmitted to the foundation. Too soft: excessive static deflection, potential instability, and amplification at resonance during startup/shutdown. The mount must be stiff enough to support the load with acceptable deflection.

Free Engineering Tool #063

Vibration Mount Selection Calculator

Select vibration isolation mounts by machine mass, operating frequency, and target isolation percentage. Calculate required mount stiffness, number of mounts, and static deflection.

Isolation Design Transmissibility Auto-Calc

Results

Total Required Stiffness

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Stiffness per Mount

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Natural Frequency

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Static Deflection

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Transmissibility

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Transmissibility

The transmissibility T defines the fraction of vibration force transmitted through the mounts:

where r = f/f_n is the frequency ratio. For isolation (T < 1), we need r > √2.

Required Natural Frequency

From the target isolation percentage, the required natural frequency is:

Required Stiffness

Static Deflection

Example — Pump on 4 Mounts

Given: Machine mass = 500 kg, Operating freq = 25 Hz, Target isolation = 90%, 4 mounts

T = 1 − 0.90 = 0.10

r = √(1/T + 1) = √(11) = 3.317

f_n = 25 / 3.317 = 7.54 Hz

k_total = m × (2πf_n)² = 500 × (2π × 7.54)² = 1,122 kN/m

k_{per mount} = 1122 / 4 = 280.5 kN/m ≈ 280.5 N/mm

Static deflection = mg/k = 500 × 9.81 / 1,122,000 = 4.37 mm

⚠️ Note: This calculator assumes undamped single-degree-of-freedom isolation. Real mounts have damping that reduces resonance amplification but slightly reduces high-frequency isolation.