Abstract: A hermetically sealed acoustic mechanism for an implantable hearing aid system having a signal processing unit having at least one electromechanical transducer coupled to the auditory system of a human. The transducer having an outer casing and at least one moving member extending outside the casing. The invention comprising a hermetically sealed bellows member having two ends and a generally cylindrical side wall. One end of the bellows member being hermetically affixed to the transducer casing and the other end of the bellows member being hermetically affixed to the moving member at a point outside the transducer casing. The side wall having a plurality of corrugations formed therein to allow the moving member to vibrate independently from the transducer casing while providing a hermetic seal protecting the interior of the transducer.