Abstract: In a telephone alerter a transducer disc is held onto a printed circuit board by an annular housing which is detachable from the board. The housing has spaced feet which are received through apertures in the board and the housing is then rotated to engage the feet with one side of the board and hold the housing in position. The transducer disc is easily removed by rotating the housing in the opposite direction to withdraw it from the printed circuit board. Preferably, the disc is retained within the housing by an O-ring retainer which is compressed between the printed circuit board and the disc. Upon removal of the housing, the disc and retainer may then be immediately withdrawn from the housing.

Abstract: A transmitter assembly for a telephone set uses a commercially available cartridge electric transmitter, by modifying the response curve. This is obtained by an adapter housing the transmitter with a first volume defined between the end of the transmitter and the end of the bore in which the transmitter fits. At the end of the bore there is an end wall with a hole therethrough, the hole covered with a layer of acoustic resistance material. A second volume is formed on the other side of the end wall, by a hollow formation on the wall of the transmitter housing of the handset. A slot is formed in the transmitter housing wall within the formation. The first volume provides damping, the hole and acoustic resistance material provides dB limitation at a particular frequency (1000 Hz) and the second volume and slot provide resonance at a second frequency (3000 Hz).

Abstract: A dynamic telephone receiver which is capable of being used in association with hearing aids, has a flux coil positioned around the pole piece and magnet assembly. To minimize the strong magnetic leakage field radiated from the air gap, which can attract pins, paper clips and other ferrous metals a shunt can be provided at the face of the receiver. However, this also shunts or at least severely attenuates the AC field produced by the flux coil for inductive coupling to hearing aids. The shunt of this invention shunts only the leakage flux from the air gap with minimal effect on the AC field from the flux coil. The shunt is in the form of a cup, with a central aperture in the front face, surrounded by an annular ring which is connected to the outer wall of the cup by narrow arms. The inner circumference of the ring is formed down towards the magnet to form a lip which attracts stray flux from the air gap. The shunt also acts to hold the receiver assembly together.