A nonlinearly broadband tuneable energy harvesting device has been designed, fabricated, and tested based on the nonlinear dynamical response of a parametrically excited clamped-clamped beam carrying a central point mass as the core element; a tuning mechanism in the form of an initial axial displacement applied to one of the clamped-clamped beam ends has been introduced to the system which enables tuning of device's natural frequency. Magnets have been used as the central point mass which generates a backward electromotive force (EMF) as they move through a coil when parametrically excited. The tuning parameter was set to a value for which the primary and principal nonlinear resonant regions become close to each other; hence, the frequency bandwidth is broadened substantially, leading to a larger amount of electrical power harvested; moreover, the nonlinear behavior, due to flexural/restoring-electromagnetic couplings, increased the operating bandwidth considerably. The system was parametrically excited using an electrodynamic shaker, and the corresponding motions of the magnets were measured. By increasing the tuning parameter, the fundamental natural frequency reduces and the system nonlinearity significantly increases; it has been discovered that when the initial axial displacement is approximately the thickness of the beam the fundamental and principal parametric resonance branches combine thus, the frequency bandwidth (and hence the range of the energy harvested) is significantly increased due to the parametric excitation, nonlinear behavior, and initial axial displacement.