Abstract: An electromagnetic transducer is disclosed that includes a pole assembly (110) comprising a central pole piece (112) upstanding from a back plate (114). A coil assembly (120) is disposed about the central pole piece (112) and rests on the back plate (114). In addition, an inverted cup-shaped permanent magnet (130) having a central opening (132) in its base (131) is positioned so that the wall (134) of the magnet circumscribes the coil assembly (120) and rests on the back plate (114). The rim of the central opening (132) in the base (131) of the permanent magnet (130) is spaced from and encircles the upper end of the central pole piece (112). Also the wall (134) of the permanent magnet (130) is of a height that the upper surface of the base (131) lies in essentially the same plane as the upper surface of the pole piece (112). A central armature (222) is supported by a nonmagnetic diaphragm (221) so as to be positioned above and spaced from the central pole piece (112).

Abstract: The disclosure relates to a ring armature electroacoustic transducer adapted for use as the receiver for telephone sets and for other purposes. The exemplary embodiment comprises the following elements coaxial about a common vertical axis: (a) a cylindrical ring permanent magnet (15) of Fe-Cr-Co material, (b) an annular disc upper pole piece (20) seated on magnet 15 and having at its inner margin a downwardly salient annular boss (30) providing an upper pole tip, (c) a lower pole piece (35) providing an annular lower pole tip (37) and aflange (36) coupling such tip (37) to the bottom of the magnet, (d) an armature support (40) within the magnet (15), (e) an annular disc armature (50) seated on the support (40), (f) a diaphragm (60) on the armature (50), and (g) a terminal plate (45) supporting such elements. The armature (50) is seated on a circular edge (90) on the support (40). The support (40), lower pole piece (35) and plate (45) form a unitary structure.