Energy, normally in the form of electricity, is a basic requirement for the modern life-style and the search for "green" energy is a major focus today. The invention provides a novel eco-friendly mechanism and device for producing mechanical power, in the form of pressure oscillations (sound waves). The energy source for driving these self-sustained oscillations is the pressure change of dry air, induced by evaporation within an acoustic resonator. The pressure oscillations may be coupled to an external load, to be concurrently converted into electricity by means of a linear motor or, alternatively, be used to drive a thermo-acoustic heat pump producing heating/cooling, as required.