A nonlinear Duffing-type dynamical system, in which the stability of equilibria is modulated in a time-dependent manner, is investigated both experimentally and numerically. This is a low-order dynamical system with some interesting available choices in the coordinate system. The system is found to exhibit a variety of interesting nonlinear behavior including ultrasubharmonic resonance. Frequency content is used to characterize periodic and chaotic behavior and their relation to the parameter space. © 2012 World Scientific Publishing Company.