The 31MIT Inertial Transducer is a device having applications as a receiver or vibrator in communications equipment, speech enhancement equipment, and relaxation systems employing vibration techniques. It is used in applications where a higher output is required than can be obtained from the Teardrop transducer. It can be used as a bone conduction receiver in direct contact with the skull or for vibration therapy, other parts of the body. In communications applications it can be attached to a lightweight helmet, effectively using the helmet shell as a loudspeaker.

Physically the device is cylindrical, having a diameter of 31mm and a height of 14.2mm. A mounting clip is available as an option. Unlike many inertial receivers which exhibit a frequency response with a single peak around 1200Hz, the 31MIT transducer has a useful response from 200Hz to 12kHz. It is available in various impedances and with either a polarised or non-polarised IEC#5 socket for connection.