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To select springs for vibration isolation, first determine the mass of the machine and the desired natural frequency of the isolation system. The natural frequency should be well below the operating frequency — typically less than 1/3 of the lowest excitation frequency.

Use the formula k = m × (2πf)² to calculate the required total spring stiffness, then divide by the number of springs to get the stiffness per spring. Verify that the static deflection is acceptable and that the springs can support the load.

For effective vibration isolation, the natural frequency should be at most 1/3 of the lowest operating frequency. For example, if a machine runs at 1500 RPM (25 Hz), the isolation system should have a natural frequency below about 8 Hz.

Lower natural frequencies provide better isolation but require softer springs and larger static deflections. Typical isolation systems target 2–8 Hz depending on the application.

The transmissibility of a vibration isolation system depends on the ratio of operating frequency to natural frequency. Isolation only begins when this ratio exceeds √2 ≈ 1.41.

At a ratio of 3 (natural frequency = 1/3 of operating), transmissibility drops to about 12.5%, meaning 87.5% of vibration is isolated. Below √2, the system actually amplifies vibrations, with the worst case at resonance (ratio = 1).

The number of springs depends on the machine size, weight distribution, and mounting configuration:

• 4 springs — most common, one at each corner for rectangular machines
• 3 springs — triangular layouts
• 6+ springs — large machines requiring distributed support

The total required stiffness is divided equally among all springs. Ensure all springs have equal stiffness to prevent tilting.

Static deflection is the amount a spring compresses under the weight of the supported mass due to gravity (δ = mg/k). It matters because:

• It determines how much the machine sinks on the springs
• It is directly related to natural frequency — larger deflection = lower frequency = better isolation
• The spring must have enough travel for static deflection plus dynamic motion
• Excessive deflection can cause stability issues

Typical isolation springs have 5–25 mm of static deflection.