Abstract: 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 energising 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 transmission through the structure or noise and vibration reduction by driving the surface out of phase with the vibration received from the structure.

Abstract: An audio system comprises, according to one aspect of the invention, an audio frequency actuator coupled to a body so as to cause the body to radiate sound when an audio signal is supplied to the actuator by a controller, and an acoustic sensor coupled to said body or to an adjacent body so as to sense acoustic vibrations in said body, the sensor being connected to the controller, whereby the controller is arranged to change the audio signal supplied to the actuator according to the vibrations sensed by the sensor.

Abstract: An acoustic transducer comprises an active element (21) which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass (20) and a foot (24) which in use engages a surface whereby audiofrequency vibrations produced by the active element are transmitted to the surface, characterised in that the foot is hingedly (25) connected to the inertial mass and the active element is located between the foot and the mass such that the angle between the first axis and the surface is less than 90°, in use.