Harvesting the maximum energy from mechanical vibration is typically achieved using a High-Q mechanical resonator. A drawback of this approach is that the mechanical resonance frequency Ω t must be matched to the source vibration frequency. In [1,2], it was shown through simulation that the Bias-Flip (BF) technique can be used to electronically tune the mechanical spring constant of a Piezo-Electric (PZ) Energy Harvesting Device (EHD) to achieve the match, and thereby achieve substantial power output over a broad range of source vibration frequencies. This paper reports two new results: 1) SPICE simulation confirms that ideal, lossless BF gives output power that is independent of frequency over a wide frequency range, and 2) experiments show that, when the source vibration frequency is far away from Ω t , BF gives improvement in output power of ∼6X.