GB2082018A

GB2082018A - Telephone sounder

Info

Publication number: GB2082018A
Application number: GB8025123A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1980-07-31
Filing date: 1980-07-31
Publication date: 1982-02-24
Also published as: HK55587A; GB2082018B; SG81384G

Abstract

A tone sounder for use in a telephone subscriber's instrument has as its sounder element a thin disc 1 of a piezo-electric ceramic, e.g. lead zirconate titanate PZT, bonded to a thin disc diaphragm 2, e.g. brass. The ceramic disc has electrical connections to both faces so that it is made to vibrate when AC is applied to it. On one face of this element is a Helmholz resonator 5, whose outlet is formed by a set of holes adjacent to another set of holes in the instrument casing. Rotation of the sounder relative to the casing varies the effective size of the outlet as the holes' overlap varies. <IMAGE>

Description

SPECIFICATION Telepone sounder The present invention relates to tone sounders, such as used in telephone subscriber's instruments, but which have other applications.

With the increasing use of electronic devices in teiephoning and elsewhere, conventional electromagnetic sounders, such as telephone bells, are becoming more and more out-moded. They are bulky and expensive, and not compatible with electronics, and are not readily adjustable.

An object of the invention is to provide tone sounders which are simple and are compatible with electronic circuitry.

According to the present invention, there is provided a tone sounder, which includes a disc of a piezo-electric ceramic material bonded to a thin disc which acts as a diaphragm when the disc is energised electrically, a Helmholz resonator one side of which is formed by the diaphragm, the other side of the resonator having a set of holes forming an aperture for sound waves to leave the resonator, and an outer casing which also incorporates a set of holes adjacent to the firstmentioned set of holes, the sounder and the portion of the outer casing having said holes being capable of relative rotation so as to vary the volume of the sound emitted by the sounder.

Embodiments of the invention will now be described with reference to the accompanying drawing, in which: Figure 1 shows in section a simple tone sounder using a ceramic disc as the sounder.

Figure 2 shows how a tone sounder embodying the invention is used in a telephone subscriber's instrument.

Figure 3 is a further embodiment of a tone sounder in a telephone instrument.

Figure 4 is a view on a larger scale of part of the arrangement of Fig. 3.

In the tone sounders to be described herein, the sounder element is a disc of a piezoelectric ceramic material, such as lead zirconate titanate-PZT, bonded to a disc, e.g. brass, which acts as a diaphragm. Electrical connections are made to the ceramic disc by metallic conductive coatings on the faces of the disc.

When a voltage is applied to these connections the PZT changes its shape, as does the diaphragm, which is normally flat, but takes up a concave or convex form depending on the polarity of that voltage. If an alternating voltage is applied, the diaphragm vibrates in sympathy to give a sound output. This sound output is greater if the electrical drive frequency coincides with the natural resonant frequency of the sound element. This sound output is, in the arrangements to be described, enhanced by the use of a Helmholz resonant cavity in front of the diaphragm.

Fig. 1 shows one way of maintaining such a device in the base of a telephone. Here the sounder element consists of a thin piezoelectric ceramic disc 1 to which a thin brass disc 2 is bonded. The sounder element is mounted by a cylindrical wall 3 and on 0 ring 4 at its nodal diameter so that there is no mechanical restraint on its vibration. Opposite the diaphragm and facing downwards there is a resonant cavity 5 with an outlet 6 on its underside. Hence a large sound output is obtained, which is reflected by the surface on which the telephone stands, and is thus distributed evenly round the room.

Note that as already mentioned, such a tone sounder has applications other than to telephones.

Fig. 2 shows further details of the mounting of such a sounder in a telephone case 8, one of the supporting feet of the instrument being seen at 9. In this case, the resonator has its lower face somewhat frusto-conical in form, with a rotatable volume control consisting essentially of a perforated disc 10 rotatable with respect to a set of fixed holes. Hence the cavity can be detuned by varying the effective area of the outlet, and hence the volume of the output sound. Thus a continuously variable volume control may be obtained by rotating the sounder and resonator assembly against the base of the telephone so that the holes coincide or are partly obstructed.

In this arrangement the electrical connections to the sounder element are made via flexible wires (not shown).

Fig. 3 shows an arrangement in which the electrical connections to the sounder element are provided by spring contacts 15, 16. Contact 1 5 engages the centre of the metallisation on the upper face of the piezo-electric ceramic disc, while contact 1 6 engages the brass disc and thereby establishes contact with the other face of the ceramic disc. In addition, the contact 16, see also the enlarged Fig. 4, is used to provide an "off" position for the volume control.

In Fig. 3 the control is so arranged that with the holes of the volume control fully open, maximum sound output is obtained. As they are effectively reduced in area by rotating the assembly against the base the sound ouput is progressively reduced until the holes are closed, which gives the minimum output.

As the assembly is rotated further, a ramp indicated at 1 7 impinges on the spring contact 1 6 to lift its contact-making portion 1 8 away from the sounder element, thus breaking the connections.

Note that in this arrangement the nodal diameter support for the sounder element uses two cylindrical walls 19, 20, each with "knife edge" to engage the element. However, the use of "knife edges" as shown in Fig. 3 is not essential to the operation. In any of the constructions illustrated the disc may be a) clamped between a cylinder and a sealing ring, as in Figs. 1 and 2; b) clamped between two cylinders, as in Figs. 3 and 4, but without the knife edges; c) fixed by a flexible adhesive to a cylinder, in which case only one cylinder is used. Such an arrangement could follow the principles of Figs. 3 and 4, but only using a lower cylinder.

Claims

1. A tone sounder, which includes a dis of a piezo-electric ceramic material bonded to a thin disc which acts as a diaphragm when the disc is energised electrically, a Helmholz resonator one side of which is formed by the diaphragm, the other side of the resonator having a set of holes forming an aperture for sound waves to leave the resonator, and an outer casing which also incorporates a set of holes adjacent to the first-mentioned set of holes, the sounder and the portion of the outer casing having said holes being capable of relative rotation so as to vary the volume of the sound emitted by the sounder.

2. A tone sounder as claimed in claim 1, and in which the ceramic material is lead zirconate titanate, the diaphragm being of brass.

3. A tone sounder as claimed in claim 1 or 2, and in which the sounder assembly rotates and as it reaches the low volume end of its travel the relative movement of that assembly and a fixed portion of the outer casing lifts a contact out of engagement with the element to cut off the supply of power to it.

CLAIMS (28Ju11981)

4. A tone sounder, such as used in a telephone subscriber's instrument, substantially as described with reference to Fig. 2 or Figs. 3 and 4 of the accompanying drawing.

5. A tone sounder, which includes a sounder assembly formed by a disc of a piezoelectric ceramic material bonded to a thin disc which acts as a diaphragm when the disc is energized electrically, and a Helmholz resonator one side of which is formed by the diaphragm, the other side of the resonator having a set of holes for sound egress arcuately located about a centre point, and an outer casing which also has a set of arcuately located holes adjacent to the first-mentioned set of holes, the sounder being rotatable about said centre point so that the degree of overlap of the holes in the two sets varies so as to vary the volume of the sound emitted by the sounder.

6. A tone sounder as claimed in claim 5, and in which when the sounder assembly when it reaches the lowest volume end of its travel in the course of its rotation operates a switch to disable the electrical power for the sounder.

7. A tone sounder as claimed in claim 6, and in which said switch operation is effected by the co-operation of a spring element on the sounder assembly and a stationary ramp, which displaces the spring element in the lowest volume position to effect said switch off.

8. A tone sounder, which includes a sounder assembly formed by a disc of a piezoelectric ceramic material bonded to a thin disc which acts as a diaphragm when the disc is energized electrically, and a Helmholz resonator one side of which is formed by the diaphragm, the other side of the resonator having a set of holes for sound egress, and an outer casing with a region having a set of holes adjacent to the first-mentioned set of holes, the sound and the outer casing being capable of relative movement so that the degree of overlap of the holes in the two sets varies so as to vary the volume of the sound emitted by the sounder, in which when said relative movement produces the lowest volume condition that relative movement also operates a switch to disable the electrical power for the sounder.

9. A tone sounder as claimed in claim 8, and in which said switch operation is effected by the co-operation of a spring element on the sounder assembly and a stationary ramp, which displaces the spring element in the lowest volume position to affect said switch off.