A novel diaphragm Stirling/thermoacoustic engine has been developed and tested that operates at high pressure and high frequency thereby delivering good power density and efficiency. This engine does not require any high tolerance or exotic parts and may thus be amenable to low cost construction in volume. Given the high frequency (500 Hz) and high working gas pressure (90 bar He) the inertia of the working gas is not negligible and thus traditional Stirling engine analysis fails to properly model such an engine. Instead, the engine is successfully modeled as a traveling wave thermoacoustic engine with a mechanical resonator (the displacer) closing the acoustic power loop. The predictions of the thermoacoustic model are compared with experimental results obtained from a prototype engine. (C) 2013 Elsevier Ltd. All rights reserved.