Abstract: A hydrogen-oxygen acoustic logging device is provided for generating acoustic waves for logging a subsurface formation when arranged in a borehole through the formation. The device is electrically driven for electrolyzing water to a gaseous hydrogen-oxygen mixture and for firing the gaseous mixture for generating the waves. The device comprises an inflatable compartment to be inflated by the gaseous hydrogen-oxygen mixture. The device further comprises a housing having an outer wall facing and closely fitting to a borehole wall portion, and provided with a recess. The recess contains the inflatable compartment and, when arranged in logging position against said borehole wall portion, defines a substantially closed wave generating chamber.