An implantable microphone for use in hearing systems includes a housing having a sidewall, a first membrane coupled to a top portion of the housing and configured to move in response to movement from an auditory ossicle, and a second membrane coupled to the sidewall such that an interior volume of the housing is divided into a first volume and a second volume. The second membrane has an opening that permits fluid to flow from the first volume to the second volume. The implantable microphone also includes a vibration sensor adjacent to the second membrane and configured to measure the movement of the second membrane and to convert the measurement into an electrical signal. The vibration sensor may include a piezoelectric sensor and/or a MEMS sensor.