US Patent 7620193 Acoustic actuators

An acoustic transducer comprises an active element which changes in length along a first axis in response to an audiofrequency input signal, the element being mounted between an inertial mass and a foot 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 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.