IMPROVEMENTS IN TELEPHONIC TRANSMITTERS
Year: 1885

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I, CHARLES DENTON ABEL, of No 28 Southampton Buildings, Chancery Lane in
the county of Middlesex Consulting Engineer and Patent Agent do hereby declare
the nature of my invention for "IMPROVEMENTS IN TELEPHONIC TRANSMITTERS
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:-
According to the present invention, the vibrating plates of telephonic microphone
transmitters are constructed of artificial carbon, prepared either from retort carbon
or from graphite, such carbon vibrating plates offer the advantage over wooden
plates of transmitting speech with a more natural sound. In addition they admit
of a considerable simplification of the construction of the microphone, as this
consists only of arranging between the two carbon plates the carbon button or
other material that unites the two carbon plates and serves for the transmission of
the electric current. This construction of microphone transmitter can be applied
to all kinds of apparatus whether those of the subscribers or those of the exchange..
By way of example I will describe this construction of transmitter applied to
apparatus for the telephonic exchange and to one for the subscribers.
The
The exchange apparatus is shewn to half full size in side view at Fig. 1, the
transmitter being shewn in section; Fig. 2 shews a plan. The microphone consists
essentially of a circular or rectangular frame A of ebonite or of wood having a
recess a containing the two carbon plates B which constitute the vibrating plates
and which are separated from each other by the insulating ebonite washer b.
plates B are of artificial carbon, either retort carbon or graphite, of from 04 in.
(1 millemeter) to 08 in. (2 millemeters) in thickness; they are adjusted in the
recess of the frame A and maintained in position by a screwed metal ring C.
Between these two carbon, vibrating plates is placed granulated retort carbon sifted
so as to obtain grains of as uniform size as possible; or they may be grains of
retort carbon or of graphite similar to lead shot. Other substances besides carbon.
may be used, being conductors or semi conductors of electricity. It is essential
that the space separating the two parts of carbon should not be completely filled
with carbon grains. The distance between the plates may vary from 08 in.
to 2 in, or even more; grains of variable size and of greater or smaller quantity
may also be used. The granular carbon may be placed in any position in the
space between the discs, and in particular in the centre of the disc such as at las
shewn at Fig. 1, and also to a larger scale at Figs. 3 and 4. On the centre of one

page_text: of the vibrating plates B is placed a ring c of ebonite or of carbon cemented with
shellac to the bottom plate. This ring c serves to confine the granular carbon d
which is thus held in the centre of the vibrating plate. This apparatus has the
effect of rendering the apparatus much more sensible and the operator can speak at
a distance of 8 in. from the disc.
In order to render the plates of a less brittle nature and yet obtain the same
effect, plates of metal D D Fig. 5 may be employed, one of which has at the centre
a disc of carbon e, while the other has an ebonite or carbon ring c serving to receive
the granular carbon d. The metal plates might also be replaced by vibrating
plates of wood or other material.
In cases where the carbon plate is made of the full diameter of the frame it may
be strengthened by constructing it with a perforated metal plate or disc of wire
gauze introduced in its thickness as shewn at Fig. 6 or again a plate of metal or
other material may have carbon dust strewn over it which is made to adhere by
means of a coating of shellac as at Fig 7. If necessary, the carbon plates may be
protected, either the end one or both, by means of a disc of wood or of metal. The
outer plate may also have a protecting shield.
Fig. 8 shews a front view of a telephonic transmitter for subscribers stations or
other localities, with the back plate removed; Fig. 9 shews a cross section.
The transmitter is formed of the two carbon plates B B having in the centre
between them granulated carbon d and mounted in a frame A which is slightly
inclined and which is carried by an arm F. The drawing shews the accessory parts
of well known construction such as the call button G, the commutator lever H
and the induction coil I. The electric current of a battery passes through the
two carbon vibrating plates and through the interposed granular carbon and it
circulates through the telephonic line or through an induction coil interposed in
the circuit.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim in respect of telephonic microphone transmitters is
1, The use of carbon vibrating plates substantially as herein described.
2. The interposition between two vibrating plates of carbon or other conducting
inaterial, of grains of carbon or other material that is a conductor or semi conductor
of electricity, substantially as herein described.
3, Arranging the granular carbon or other material referred to in the preceding
claim, within an enclosure at the centre of the space between the two vibrating
plates substantially as herein described.
4, The various modes of constructing vibrating plates wholly or partly of carbon,
with granular carbon between them, as herein described with reference to the
accompanying drawings.
5, The portable telephonic transmitting apparatus for exchange offices combined
and arranged as herein described with reference to Figs. 1 and 2 of the drawings.
6, The telephonic transmitting apparatus for subscribers and for other purposes,
combined and arranged as herein described with reference to Figs. 8 and 9 of the
drawings..