This paper presents the development of a broadband, multi-frequency acoustic energy harvester. The devised energy harvester contains an optimized Helmholtz resonator with conical cavity and a piezoelectric composite plate. The shape and dimensions of the resonator are selected based on the 3D pressure acoustics analysis in COMSOL Multiphysics®. In addition, a cantilever beam, made up of a brass base, a copper rod and a steel sheet, is integrated with the harvester’s piezoelectric plate to add an extra degree of freedom to the device. The developed harvester exhibited three peaks at 1501, 1766 and 1890 Hz frequencies, which correspond to the three resonant frequencies of the harvester. Furthermore, the harvester, when subjected to 130 dB sinusoidal SPL and 1501 Hz resonant frequency, generated a maximum power of 214.23 μW. However, when the harvester is operated under random (real) SPL in the vicinity of household electric generated, it produced about 250 and 265 mV output AC and DC voltage levels respectively.