This work presents an approach for increasing operational bandwidth of a vibration energy harvester in low-frequency environments by effectively exploiting contact-based frequency up-conversion. It was implemented by a couple of low-frequency resonators with appropriately spaced natural frequencies impacting high-frequency piezoelectric generators when the device is harmonically excited in 10-40 Hz range. A proof of concept was designed, modeled, fabricated and characterized, demonstrating improved power and bandwidth performance (up to 37 μW and 9 Hz at 1g) with respect to traditional single-resonator designs. © 2014 The Authors. Published by Elsevier Ltd.