In this paper, we present an experimental and theoretical study of a nonlinear oscillator for energy harvesting applications. The collected energy comes from ambient vibrations as external energy sources. Specifically, we consider both periodic (e.g. 50Hz or 60Hz power line couplings) and stochastic sources (e.g. human-made devices, automobiles, train, etc.). The proposed mechanism is a double-well oscillator with a large amplitude response over a broad range of frequencies. Such system improves proposed scavengers based on linear mechanical principles, which only give appreciable response if the dominant ambient vibration frequency is close to the mechanical resonance. At the same time, it improves nonlinear harvesters (e.g. bi-stable) proposed in the literature by decreasing the vibration amplitude required to exceed the potential barrier of the double-well function through the benefit of the additive sinusoid. Modeling, numerical simulations and experiments are here reported to show a good accordance with expectations.