Ideal one-dimensional linear model
Equivalent Linear Spring Stiffness
Combine two to five positive tangent spring rates in a true one-dimensional series or parallel arrangement. Optional natural frequency uses an ideal undamped single-degree-of-freedom model.
Equivalent ideal model
MIT OpenCourseWare Precision Engineering Principles states these compliance/stiffness addition rules. A separate MIT solid-mechanics laboratory note derives the two-spring series result from equilibrium and compatibility.
The frequency result applies only to a rigid effective mass on massless linear springs with one degree of freedom and no damping. MIT Mechanics and Materials states this boundary explicitly. For real isolators, include the effective mass of mounts/springs, geometry, damping and all coupled modes.
Unit correction: input is always N/mm and kg. Results also show N/m and lbf/in, using exact SI definitions: 1 lbf=4.4482216152605 N and 1 in=25.4 mm. The old toggle reinterpreted unchanged numbers and could alter physical stiffness by 5.71×.
