[0001] The invention relates to a telephone bell assembly comprising two bells which are
arranged to be struck alternately by a single hammer.
[0002] Conventional telephone bell assemblies comprise two bells each of a particular resonant
frequency which are struck by a single hammer operated by an electromagnetic motor
unit. The bells are placed on opposite sides of the hammer so that they are struck
alternately as the hammer is swung from side to side by the motor unit.
[0003] Such bell assemblies are relatively bulky items which, while - satisfactory in the
traditional telephone instruments which have a relatively large volume, take an unacceptably
large proportion of the interior volume of smaller instruments. In particular the
depth of the instrument may be insufficient to house the conventional bell assembly.
A possible solution to this problem, is to reduce the depth of each bell but in order
to maintain the same musical tone it is then necessary either to increase the diameter
of the bell or to make the bell from thinner material. The preferred practical solution
is to increase the diameter of the bells as thin bells do not possess the necessary
robustness. This however will increase the overall width of the assembly and again,
may cause the assembly to occupy an unacceptably large proportion of the interior
space of the instrument.
[0004] It is an object of the invention to produce a more compact telephone bell assembly.
[0005] The invention provides a telephone bell assembly comprising two bells which are arranged
to be struck alternately by a single hammer characterised in that one of the bells
is inverted with respect to the other, that the mouths of the bells overlap and that
the wall of at least one of the bells is slotted to enable the bells to nest one within
the other. By overlapping the bells the width occupied by the assembly can be reduced
or an assembly having larger diameter bells may be accommodated in the same width
and by slotting the bells a reduced depth may be achieved.
[0006] In an arrangement in which the bells are arranged symmetrically about the hammer,
the hammer is located between the overlapping portions of the bells. With this arrangement
the degree of overlapping of the bells is limited in that the hammer must be able
to strike each bell within its limit of travel.
[0007] In an alternative asymmetric arrangement the hammer is arranged to strike the inside
of the wall of one bell and the outside of the wall of the other bell. This arrangement
allows a substantial overlapping of the bells to provide a particularly compact arrangement.
It may also permit an easier adjustment of the bell position with respect to the hammer.
[0008] Embodiments of the invention will now be described, by way of example, with reference
to the accompanying drawings, in which:-
Figure 1 shows a plan view of a first embodiment of a telephone bell assembly according
to the invention.
Figure 2 is a cross-sectional elevation on line X-X of Figure 1,
Figure 3 is a plan view of a second embodiment of a telephone bell assembly according
to the invention, and
Figure 4 is a cross-sectional elevation on line Y-Y of Figure 3.
[0009] The telephone bell assembly shown in Figures 1 and 2 comprises two bells 1 and 2,
a hammer 3 and an electromagnetic motor unit 4. The bells and motor unit are mounted
on a base plate 5, the bells being mounted by pillars 6 and 7. The electromagnetic
motor unit comprises an arm 8 connected to an armature 9 which is pivotted on a permanent
magnet 10. Two series connected coils 11 and 12 are mounted on either side of the
magnet 10 and when connected to an a.c. ringing voltage cause the armature 9 to rock
about its pivot as each end is in turn attracted towards the respective coil 11 or
12. The rocking of the armature causes the arm 8 on which the hammer 3 is mounted
to swing from side to side thus causing the hammer to alternately strike the bells
1 and 2.
[0010] The bell 2 is inverted with respect to the bell 1 and is provided with two slots
13 and 14 to enable the depth of the assembly to be reduced by allowing the walls
of bell 1 to pass through those of bell 2. The bell 1 is also provided with a slot
15 to allow the arm 8 to pass through the bell so that the hammer 3 can be located
between the bells.
[0011] The bells 1 and 2 may be pressed from steel or brass sheet 0.030 inches thick and
have a diameter of 2 inches. Bells of these dimensions and materials produce a tone
similar to that of the conventional bell assembly. Different tones may be produced
by altering these dimensions.
[0012] An alternative arrangement in which the bells can be overlapped to a greater extent
is shown in Figures 3 and 4. In this arrangement the hammer 3 is located between the
non-overlapping portions of the bells 1 and 2. The bell 1 is provided with three slots
20, 21 and 22 the slot 20 being provided to enable the arm 8 to pass through the wall
of the bell 1 and the slots 21 and 22 being provided to enable the wall of bell 2
to pass through the wall of bell 1. It can be seen that with this arrangement only
one of the bells need be slotted. It is necessary with the arrangement shown in Figures
3 and 4 to provide a hole in the base of bell 1 to allow the supporting pillar 7 of
bell 2 to pass through bell 1 to the base 5. Alternative mounting arrangements could
be used, for example a bracket attached to the base 5 could carry an arm which supports
bell 2 or the bell 2 could be mounted on the body of a telephone instrument with the
base 5 subsequently assembled into and mounted on the body so that the bells are located
in the desired positions. Instead of providing the slot 20 in bell 1 the arm 8 could
be cranked so that it passes over the wall of the bell 1 but the hammer 3 still strikes
the walls of the bells. The arm 8 could further be cranked so that the motor 4 is
not offset from the bells 1 and 2 thus providing an even more compact assembly.
1. A telephone bell assembly comprising two bells which are arranged to be struck
alternately by a single hammer characterised in that one of the bells is inverted
with respect to the other, that the mouths of the bells overlap, and that the side
wall of at least one of the bells is slotted to enable the bells to nest one within
the other.
2. A telephone bell assembly as claimed in Claim 1, in which the hammer is located
between the overlapping portions of the bells.