Structural damping is often assumed to be viscous and linear which leads to comparatively straightforward vibration analysis. In the case of vibration isolation mounts this assumption of linearity is particularly questionable and one might want to know the effect of a nonlinear damping characteristic on the isolation performance. This paper considers the isolation performance of a single degree of freedom system with cubic damping. Previous work has considered the case of harmonic base excitation in which cubic damping is less favourable than linear damping. This work is summarised briefly here and extended to random base motion. The study is predominantly experimental in which cubic damping is realised using simple velocity feedback control. The rig is first described and characterised in its passive state prior to implementing linear and cubic velocity feedback. It is found that, unlike the case of harmonic base excitation, cubic damping offers very similar performance to linear damping. The reason for this difference in behaviour is identified by considering the probability density functions of the response variables.
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