A hermetically sealed actuator design for absorbing and reducing the effect of sound or vibration energy from a vibrating surface. The device comprises a body (1) containing a magnetostrictive core (2-6) a reaction mass (7) for energizing the actuator by compression, and a bearing or lever system to control the movement of the reaction mass. The actuator has a foot (11) for receiving the vibration from the structure into the device and a sensor (13) for monitoring vibration levels. The device can also function as an audio transmitter whereby it vibrates the surface onto which it is mounted and can be used for audio trans-10 mission through the structure or noise and vibration reduction by driving the surface out of phase with the vibration received from the structure.