US Patent 11450302 Loudspeaker with magnets in ferrofluid

A loudspeaker is provided with a motor assembly having at least one planar coil and first and second magnets magnetized in a magnetized direction perpendicular to direction of coil movement and perpendicular to a central axis of radiation of the loudspeaker. Ferrofluid is disposed between a diaphragm and the first and second magnets. Third and fourth magnets are disposed outside the first and second magnets and are magnetized in a direction parallel to the direction of coil movement and perpendicular to the magnetized direction of the first and second speakers.