Abstract: An electromagnetic transducer for sound and ultrasound reproduction includes a substantially flat coil coupled to a diaphragm that is near to and facing the North or South side of a magnet. A very thin membrane made from a non-magnetic but electrically conductive material is independently mounted from the diaphragm and faces it. An AC signal in the coil results in diaphragm movement and “modulates” the permanent magnetic field. The modulating field generates a current in the membrane, which, upon further interactions, causes the membrane to move. The two independently moving surfaces each generate sound and result in an unusually flat SPL/frequency response, with unusually low narrow-band intensity variation and very low distortion. The transducer is also unique among electromagnetic transducers in that the force acting on the membrane is uniformly distributed over much of it, as in an electrostatic sound transducer.

Abstract: A variant of a planar magnetic transducer for sound and ultrasound reproduction includes a substantially flat coil fixed on a diaphragm. A source of a non-varying magnetic field is disposed on one side of the diaphragm; a thin, electrically conductive, non-magnetic membrane is disposed on the other side. An AC signal in the coil results in diaphragm movement and modulation of the non-varying magnetic field. The modulating field generates a current in the membrane, which, upon further interactions, causes the membrane to move. The two independently moving surfaces, each of which produce sound, together result in an unusually flat SPL/frequency response, with very low narrow-band intensity variation and distortion. The forces acting on the moving planes are substantially uniformly distributed on active parts and the force per unit area is high. In embodiments directed to reproducing sound in a limited frequency band, the driver can be very efficient.