Pattern voice coil transducer having permanent magnet plates of a single polarity

Electromechanical transducer apparatus which comprises,

• permanent magnet field generating means comprising a first assembly of permanently magnetic material displaying a sole pattern of magnetic poles solely of one polarity, a second assembly of permanently magnetic material spaced from the first assembly and displaying a second sole pattern corresponding to the first pattern of poles solely of opposite polarity to that of the first pattern, and means orienting said assemblies relatively to one another whereby a flux pattern is set up between the first and second patterns of poles across the space separating the two assemblies consisting of a pattern of similarly directed but alternately inclined field zones, said assemblies each comprising a sheet of ferrite material each displaying the respective magnetic pole pattern on one face thereof,
• an electrically insulating diaphragm in said space,
• conductors on said diaphragm, each conductor extending substantially across a respective field zone,
• and means connecting the ends of said conductors into a circuit in the sense that forces on said conductors reinforce in a chosen direction transverse to the diaphragm to move the diaphragm when current flow is in one direction in said circuit, and forces on the conductors reinforce to move the diaphragm in the opposite direction when current flow in the circuit is in the opposite direction.