Vibration transducers

A loudspeaker comprising:

• a member having opposed faces and a capability to sustain and propagate input vibrational energy by bending waves in at least one operative area extending transversely of thickness to have resonant mode vibration components distributed over said at least one area and have predetermined preferential locations or sites within said area for a transducer for exciting the member, and
• a transducer mounted on said member at one of said locations or sites for vibrating member to cause it to resonate forming an acoustic radiator which provides an acoustic output when resonating, the transducer comprising:
• a motor coil assembly having a coil rigidly fixed to a tubular member, and
• a magnet assembly, having opposed pole pieces, the periphery of one of said pole pieces being disposed within and adjacent to the motor coil assembly, and the periphery of the other of said pole pieces being disposed outside of and adjacent to the motor coil assembly,
• wherein the magnet assembly has a central attachment portion rigidly attached to the member to be vibrated,
• wherein the motor coil assembly surrounds and is spaced from said central attachment portion of the magnet assembly and has a surrounding attachment portion rigidly attached to one face of the member in spaced relation to said central attachment portion of the magnet assembly, and
• wherein the motor coil assembly and the magnet assembly move in opposite directions when a signal current is applied to the motor coil assembly, whereby the motor coil assembly and the magnet assembly apply a couple to the member through their respective spaced attachment portions to launch bending waves into the member.