Abstract: A downhole thermoacoustic device comprises a heater with a terminal chamber, connected to a source or radiator of acoustic oscillation, including a hollow housing having mounted therein a longitudinal shaft carrying coils with cores in the form of a plurality of flat rings of a magnetostrictive material, operable as the active elements adapted to generate acoustic oscillation. Accommodated intermediate the coils is a member for focusing the acoustic field, in the form of a sleeve, while the longitudinal shaft carries a tube-shaped reflector of acoustic oscillation internally of the core of each coil. The top and bottom portions of the hollow housing of the radiator of acoustic oscillation have mounted therein damping elements including sleeves of a resilient material, while a heat-insulating member including a sleeve with a fluted surface is provided intermediate the terminal chamber of the heater and the hollow housing of the radiator.