Improvements in Telephone Transmitters, and Arrangements for same.
Year: 1894

page_text: Date of Application, 24th Feb., 1894
Complete Specification Left, 24th Dec., 1894-Accepted, 24th May, 1895
PROVISIONAL SPECIFICATION.
Improvements in Telephone Transmitters, and Arrangements
for same.
ALFRED CHARLES BROWN of Winchester House Old Broad Street in the
City of London, do hereby declare the nature of this invention to be as
follows:-
In order to develope the maximum power of telephone transmitters, using any
kind of carbon variable resistance or tension regulator, and especially of those.
kinds using granulated carbon, variably compressed between a diaphragm and
back electrode of various shapes, I find it is absolutely necessary to clamp the
diaphragm in a particular way; that is between a hard and rigid flatly ground, or
faced ring seating on the one side, and a resilient compressible or elastic spring
ring on the other, the said spring ring being compressed by the clamping to a
certain definite pressure (depending on the composition, thickness and diameter of
the diaphragm used) and no more, and to secure that such clamping pressure. shall
thereafter remain absolutely invariable.
Where granulated carbon variable resistances are used also I find it is necessary
that the back electrode shall be exceedingly rigidly fixed to the rigid ring seating,
and that the latter should be composed of a very hard and unyielding material.
To fulfil the above-mentioned conditions, I therefore construct my transmitter as
follows:-
I take a back block, which may be either of metal, carbon, glass, porcelain or.
stoneware, or other hard material not subject, or only very little subject to change
from ordinary atmospheric causes.
Of this I make a ring seating for the diaphragm and take care that the said
ring seating is turned or ground perfectly flat on the diaphragm side. In or near
the centre of this ring back block, I then cement, by means of a very hard, rigid
cement such as shellac, or plaster of Paris, the back carbon electrode, which may
be of any of the many well-known, previously used shapes, such as a plain plate or
block, having grooves or projections on its surface.
I find however, the most efficient shape for this purpose, and the one which I
therefore prefer to use, consists of a short cylindrical block of carbon placed with
one of its end faces towards the diaphragm at or near the centre thereof, and
having an edge or ridge all round projecting towards the diaphragm, the said.
projecting ridge not quite touching the diaphragm, but coming sufficiently near
thereto, to prevent the escape of the granules which are contained in the space
between the back electrode and the diaphragm, and are carefully sifted so as to
make quite sure that each individual particle is too large to drop through the
small intervening space, which space may be further packed round with silk, wool,
cotton or similar fibrous material.
Or the said ridge may ouly extend partly round the carbon block, or may take
other directions, in which case the granules are confined by the packing.
.I do not however in any way limit myself to the above form of electrode.
Or instead of being cemented into the back-block, or diaphragm-ring-seating,
the back electrode may be formed solid therewith out of one piece of carbon, but
in this case a ring of insulating material preferably composed of mica, or similar
hard substance, must be interposed between the diaphragm and back block to
prevent direct electrical connection.

page_text: Round near the edge of the diaphragm on the front side, or side which comes
opposite to the back-block, 1 then place the before-mentioned compressible but
resilient spring ring which I preferably make of a small hollow india-rubber tube,
baving rather thick sides compared to the diameter of the hole, so that the latter
may not be flattened quite together or collapsed by the amount of clamping
pressure used.
Or I may make the spring ring of a helix of any spring wire, which is then laid
round in a block of the required diameter of the spring ring and partially collapsed
by means of pressure applied to another block, placed on top of the spring, and to
which block a small rotative movement is imparted during the application of the
collapsing pressure. This causes each of the turns of the spiral to turn over and
partially lie down in one direction and in which position each turn separately
exerts a resilient upward pressure throughout the required short range. Or I
may use for the spring ring a number of separate or combined springs of any form,
such that they will, when placed in position apply invariable spring pressure at
numerous points round near the edge of the diaphragm, and that such pressure
shall extend through a short range to allow a little movement of the diaphragm
under heavy vibration and slight contractions in the fixed clampings without
causing either any great variation in the amount of the pressure or any
permanent set.
I also take care that when this spring clamping ring, however formed, is placed
in position on the diaphragm, that it comes in or near the middle of the breadth
of the flat hard ring seating on the other side, so that the diaphragm may be
perfectly evenly clamped and not buckled or unduly strained, in any one place.
Over the spring clamping ring I then place another ring seating formed in a
containing case also made of a bard, rigid material like the back one, and which
case may also be formed into a mouthpiece on its front side, or be adapted to have
a separate mouthpiece screwed into or otherwise affixed on to it, and having a
flange of a larger diameter than the diaphragm projecting backwards over the
diaphragm and back block and adapted to be affixed to the latter also by a very hard
and rigid cement, the said cement being applied, and the clamping made preferably
in the following manner :-
The back-block is first laid on a flat horizontal surface. The granules which
may consist as heretofore of any hard form of carbon or similar substance, are then
put into their proper space over the back electrode, which is fixed into the back-
block, which latter also carries or forms the hard ring seating for the back of the
diaphragm, care being taken that the quantity of granules is insufficient to jam or
bulge the diaphragm. The latter is then placed on its seating, the spring ring
laid on the top of it and the front casing inverted thereover. The whole together
is then again carefully inverted, so that the front casing lies on the horizontal
surface. A weight of definite amount is then put on top of the back-block, the
exact amount depending on the composition and thickness of the diaphragm. If
the latter be of carbon, and about millimetre thick by about 55 millimetres or
2 inches diameter, which I find to be a very good construction, a weight of
about 2 lbs., should be applied. While this weight is on the back-block, the
cement is run round the edge of the latter so as to firmly unite it to the backwardly
projecting flange of the front casing, the said cement being allowed to thoroughly
set before the weight is removed, when it will be found that the clamping pressure
on the diaphragm is of the exact amount and quality to give the maximum speaking
power, and that the latter will thereafter remain invariable.
Spring pressure may of course be substituted for the weights during cementing
if the same amount of pressure be obtained, but I prefer weights as being more
simple and less liable to accidental variation.
The diaphragm, granules, and back electrode are then connected in series in
circuit with a battery and preferably the primary coil of an induction coil, the
secondary coil of which is to line and receivers, or in any other usual well
understood way of connecting. Telephone transmitters, and contact with the

page_text: various parts of the transmitter may be secured in a variety of well understood
manners. If the back-block and ring seating is a conductor and has a separate
back electrode fixed therein by an insulating cement, I prefer to make those pieces
respectively the positive and negative poles of the transmitter. If the back ring
seating be not made of a conductor, connection with the diaphragm may be
established through the spring ring where the latter is metallic, or in other obvious
or usual ways.
I prefer to connect these transmitters by means of a flexible cord with a receiver
mounted so as to stand on a shelf, and preferably carry the induction coil in its
base, or the receiver may be suspended overhead and the induction coil be fixed
separately, the receiver in either case having a trumpet-shaped mouthpiece, to
enlarge the sound which with these transmitters is loud enough to be heard in any
part of a room without putting the receiver to the ear, even when a considerable
resistance is interposed in the line circuit.
I also provide on the back or other part of the transmitter, a small key adapted
to be pressed by the finger while speaking, so as to complete the battery or local
circuit, while speaking, and also preferably to short circuit, or cut out the secondary
coil where an induction coil is used, when the key is released, leaving the receiver.
only in circuit, which arrangement by reducing the line resistance enables a greater
number of stations to be run in series on one wire or circuit.
The transmitters can thus be laid on a desk when not in use, and picked up
and conveniently applied to the mouth for speaking, and any station out of a
number in series on one line can be spoken to by simply calling into the transmitter
the proper name, the sound being loud enough to attract attention without any bell
or other signal.
Dated this 24th day of February 1894.
COMPLETE SPECIFICATION.
Improvements in Telephone Transmitters, and Arrangements
for same.
I, ALFRED CHARLES BROWN, of 129, Algeruon Road, Lewisham, in the
County of Kent, Electrician, do hereby declare the nature of this invention and
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-
My invention relates to telephone transmitters, and while particularly adapted
to that class comprising a diaphragm and back electrode with granulated carbon
compressed between the electrode and diaphragm as to certain features, is not
limited as to others to this class of transmitters, being applicable to transmitters
using any form of variable resistance.
My invention consists first in a telephone transmitter in which the diaphragm is
seated on one side against an elastic bearing near the edge of said diaphragm,
and further of a diaphragm having a rigid seat on one side and an elastic bearing
composed of a springy or elastic ring forming a seat for the edge of the diaphragm
upon the other, and which elastic ring is compressed exactly to a predetermined
extent and set so as to remain invariable.
My invention consists further of an improved electrode for telephone transmitters
composed of a short and preferably cylindrical block of carbon placed with one of
its end faces towards the diaphragm at or near the centre thereof, and having an
edge or ridge all round projecting towards the diaphragm at an angle of about 45°,
the said projecting ridge not quite touching the diaphragm, but coming sufficiently
near thereto to prevent the escape of the granules which are contained in the space
between the back electrode and the diaphragm. In the centre of the cavity formed

page_text: by the projecting ridge is placed a disc of cotton wool covering the flat part of
the bottom filling up the space between the latter and the diaphragm so as to
confine the granules in the triangular space between the inclined side of the
electrode, the packing, and the diaphragm, which granules are carefully sifted so
as to make quite sure that each individual particle is too large to drop through
the small intervening space, which space may be further packed round with silk,
wool, cotton, or similar fibrous material; or the said ridge may only extend
partially round the carbon block, or may take other directions in which case the
granules are confined by the inclined side, diaphragm, and packing; or the electrode
may be formed as the frustum of a cone and have a ring of cotton wool or other
similar springy packing material placed round it so as to confine the granules onto
the inclined edge of the cone; or the back electrode may be formed in other
obvious manners, the essential feature being that there shall always be an inclined
surface extending towards the diaphragm (and preferably at an angle of about 45°)
and which may take any longitudinal direction over or along the face of the
electrode, but which always has running parallel to its length and at a slight
distance from its upper edge, a layer or strip of cotton wool or other springy elastic
packing serving to confine the granules in the triangular cross-sectioned space
contained between the diaphragm, the inclined surface of the electrode, and the
wool or other packing.
My invention consists further of certain improvements in the method of
constructing telephone transmitters as will be hereinafter more particularly
described.
.
In the accompanying drawings I have illustrated my invention, in which
Fig. 1 is a central vertical section through the transmitter ;
Fig. 2 is a section on line c-x of Fig. 1;
Figs. 3 and 4 are similar sections of transmitter showing modified forms of the
electrode ;
Figs. 5 to 10 are views showing different forms of electrode;
Figs. 11 and 12 show details of the manner of mounting or supporting the
transmitter.
In Figs. 1 and 2 the casing of the transmitter is shown at F, having a flaring
mouthpiece F, with the walls extending to the rear as at sufficiently to carry
the back seating for the diaphragm and its attached electrode. The diaphragm is
shown at A, with an elastically compressible ring E between it and the face of the
casing F. Upon the opposite side of the diaphragm is the electrode C secured in
place as hereinafter explained by cement or plaster of Paris H, extending between
the same and a ring B which forms a back bearing for the diaphragm, and which
is secured by cement or plaster of Paris H to the wall of the casing F. The
electrode C is here shown as a circular block having inclined edges extending
towards the diaphragm at an angle of about 45°, the packing D being arranged
centrally in the central cavity c¹ so formed so as to cover the flat surface and form
with the inclined face c a triangular cross-sectioned space in which the granules
are located.
In Figs. 3 and 4 a modification is shown in which the electrode is in the
form of the frustum of a cone, and on the inclined faces c. c. of the cone are
located the carbon granules G, these granules being prevented from escaping by
packing D of silk, wool, cotton, or the like, surrounding the granular field as
shown. This packing has the further property in all cases of always exerting a
continuous elastic pressure on the granules tending to slightly force them against
the incline c towards and onto the diaphragm A. I prefer to make the diaphragm
of carbon, or of thin platinised or silvered glass, or glass covered with any other
conductor, but I do not limit myself to any particular composition for the
diaphragm.
As a further illustration as to how my invention can be carried out, reference is
made to Figs. 5 and 6, in which the electrode has straight V-shaped channels, and
in these chaunels sufficient packing D is placed to fill substantially one half of

page_text: each space, and in the other half the granules G are placed, thus securing precisely
the same relative arrangement and action.
In Figs. 7 and 8 the back electrode C is channeled or recessed, the channel
having a flat base and inclined walls c, along the flat base the packing D is laid
thus forming two triangular-shaped channels one on each side thereof, into each of
which the granules G are placed.
In Figs. 9 and 10 the recesses or channels are formed with one vertical side c¹.
a horizontal bottom, and an inclined side c opposite the vertical side, the packing D
and granules G being arranged as shown in Fig. 9.
It is obvious that the electrode may be made in various forms, but the essential
feature of this part of my invention lies in confining carbon granules within a
triangular cross-sectioned space formed by the diaphragm on one side, the inclined
surface of the electrode on the second side, and the spring packing material on the
third side, the electrode having grooves or projections with inclined sides which
may take any longitudinal direction over its surface and followed always by parallel
strips of cotton wool or springy packing material serving to form the third wall of
the said triangular spaces, and the said electrode having no other faces in contact
with granules.
In this channel the granules are confined and are by the springy packing
yieldingly compressed against the inclined face and the diaphragm so that the
springy pressure of the packing will constantly tend to cause the granules to shift
their position by moving up the incline towards the diaphragm instead of towards
the angle at the base of said incline.
This construction permits of the entire space between the diaphragm and back
electrode, remaining after the introduction of the packing, being filled with
granules, while avoiding any possibility of their falling between two rigid opposing
surfaces or into grooves or recesses between projections, both opposing facings of
which are hard, rigid, and unyielding, and thereby becoming packed or jammed
and thus practically short circuiting the transmitter and preventing the free motion
of the diaphragm, objections to which existing transmitters are subject.
The small space between the upper edge of the inclined faces c of the back
electrode C and the diaphragm A may also be packed with similar light packing,
but if the distance be carefully limited by the process hereinafter described, and
the granules sifted so as to make quite sure that each individual particle used is too
large to pass through the small intervening space x, I do not find any such packing
necessary or desirable.
In order to fix the carbon back electrode C into the ring or back block B in
such way that the upper surfaces or top edges of the projections or inclined faces c
of the electrode shall approach very closely to without touching the diaphragm,
I prefer to place the ring B with its face downwards upon a sheet of glass or other
flat surface, with a piece of writing paper or metal of requisite thinness, say
about 1 inch, between the glass and the electrode which is also inverted upon the
paper in the centre of ring B. Around the electrode I place a suitable core
capable of being afterwards removed from the front side, to produce the requisite
hollows between ring and electrode, and then fill in with plaster of Paris, or other
rigid cement, which is allowed to thoroughly set before the cores are removed.
By this method of construction I secure an instrument wherein the separation of
the back electrode from the diaphragm is made exact and uniform for any number
of instruments and without the difficulty which would necessarily arise from the
attempt to secure the desired separation by fastening the electrode in place by
means of its back surface in the usual way.
Or instead of being cemented into the back block B the back electrode may be
formed solid therewith out of one piece of carbon, but in this case a ring of
insulating material preferably composed of mica, or similar hard substance, of
definite. thickness must be interposed between the diaphragm and: back block to
prevent direct electrical connection through the seating.

page_text: In mounting the diaphragm so as to fulfil the conditions of efficiency above
referred to I place near the edge of the diaphragm on the front side, opposite.to
the rigid seat, a compressible but resilient spring such as E, which I preferably
make of a small hollow india-rubber tube, having rather thick walls compared to
the diameter of the hole, so that the latter may not be flattened quite together or
collapsed by the amount of clamping pressure used; or, I may make the spring
ring of a helix of any spring wire, which is then laid round in a block of the
required diameter and partially collapsed by means of pressure applied to another
block, placed on top of the spring, and to which block a small rotative movement
is imparted during the application of the collapsing pressure. This causes each of
the turns of the spiral to turn over and partially fold or lie down in one direction,
in which position each turn separately exerts a resilient upward pressure throughout
the required short range. Or I inay use for the spring ring a number of separate
or combined springs of any form, such that they will, when placed in position, apply
invariable spring pressure at numerous points round near the edge of the diaphragın,
and that such pressure shall extend through a short range to allow a little movement
of the diaphragm under heavy vibration and slight contractions in the fixed
clampings without causing either any appreciable variation in the amount of the
pressure or any permanent set.
I also take care that when this spring ring, however formed, is placed in position
on the diaphragm, that it comes in or near the middle of the breadth of the flat
hard ring seating on the other side, as shown in Figs. 1 and 3, so that the
diaphragm may be perfectly evenly clamped and not buckled or unduly strained in
any one place.
In building up the transmitter the back block or ring B with the electrode C
and packing D attached is laid face upwards on a flat horizontal surface. The
granules G, which may consist as heretofore of any hard form of carbon or similar
substance, are then put into their proper space, care being taken that the quantity
is not sufficient to jam or bulge the diaphragm. The latter is then placed on its
seating, the spring ring laid on top of it, and the front casing inverted thercover.
The whole together is then carefully reinverted so that the front casing lies on the
horizontal surface. A weight of definite amount is then put on top of the back
block B, the exact amount depending on the composition and thickness of the
diaphragm. It the latter be of carbon, and about millimetre thick by about
55 millimetres or 2 inch in diameter (which I find to be a very good construction),
a weight of about 2 pounds should be applied. While this weight is on the back
block plaster of Paris or other rigid cement is run around the edge of the latter so
as to firmly unite it to the backwardly projecting flange of the front casing F, the
said cement being allowed to thoroughly set before the weight is removed, when it
will be found that the clamping pressure on the diaphragm is of the exact amount
and quality to give the maximum speaking power, and the latter will thereafter
remain invariable.
Spring pressure may of course be substituted for the weights during cementing
if the same amount of pressure be obtained, but I prefer weights as being more
simple and less liable to accidental variation.
As will be obvious the clamping pressure must be determined for each different
construction of instrument, but the best pressure having been once exactly
determined by the use of the weight, spring, or other device, any number of
instruments may be rapidly and easily constructed by using the same weighed or
measured pressure and the best results obtained from each instrument.
The diaphragm, granules, and back electrode are connected in circuit with a
battery and preferably the primary coil of an induction coil, the secondary coil of
which is to fine and receivers, or in any other usual well understood way of
connecting telephone transmitters, and contact with the various parts of the
transmitter may be secured in a variety of well understood ways.
If the ring
seating B is a conductor and has a separate. back electrode fixed therein by an

page_text: insulating cement, I prefer to make these pieces respectively the positive and negative
poles of the transmitter. If the ring seating B be not made of a conductor,
connection with the diaphragm may be established through the spring ring E
where the latter is metallic, or in other obvious or usual ways.
Fig. 11 shows one way of making the connections in which contact with the
back carbon electrode is secured by means of a spring 2, the spring being affixed to
a back block or base 3, and to this base the transmitter 1 is bodily fixed by screws +
passing through the base 3 and screwing into the brass ring seating B, which
screws also form a means of making an electrical connection from the diaphragm ;
or the connections may be made and the transmitter fixed to a support in any other
convenient way. As shown in Fig. 12 when the transmitter 1 is to be held in the
hand, I provide on the back or other part a small key such as 6, adapted to be
manually pressed while speaking so as to make contact with the back electrode C
and complete the circuit. The transmitters arranged in this way can be laid on a
desk when not in use, and picked up and conveniently applied to the mouth for
speaking, and any station out of a number in series on one line can be called by
simply speaking into the transmitter the proper name, the sound being loud enough
to attract attention without any bell or other signal.
Having now particularly described and ascertained the nature of this inven
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. In a telephone transmitter the arrangement of a diaphragm having a rigid
ring seating ou one side and an elastic spring ring upon the other side, said spring
ring and diaphragm together being compressed to a definite predetermined degree
and thereat rigidly and permanently affixed, substantially as and for the purposes
above set forth.
2. In a telephone transmitter a carbon electrode having one or more grooves or
projections running in any longitudinal direction over its surface, one of the walls
of such grooves or projections being inclined to the face of the diaphragm at an
angle of approximately 45° and having parallel thereto and at a short distance
therefrom a strip of cotton wool or other springy packing following the direction
of such grooves or projections, so as to form together with the diaphragm, and
inclined face of the electrode, a triangular space having two rigid and one yielding
sides in which alone the granules are confined.
3. In a transmitter, an electrode in the form of the frustum of a cone in
combination with an elastic packing forming a ring around said electrode, and a
mass of granules filling the triangular space between the cone, the packing ring, and
the diaphragm, and subjected by said ring to an elastic pressure exerting a constant
tendency to cause the granules to move up the incline of the cone towards and on
to the diaphragm, and the said electrode carrying no granules on any other
surfaces, substantially as set forth in reference to Figs. 3 and 4.
4. The several arrangements of my improved telephone transmitters shewn
respectively in the drawings and adapted to operate substantially as hereinabove
set forth.
5. The herein described improvement in constructing telephone transmitters
having a diaphragm and rigidly held back electrode separated from the diaphragm
by a narrow space, consisting in cementing the said electrode to a back piece while
the two are supported in proper relative position with a gauge piece or plate
between the electrode and its temporary support, and subsequently securing the
said back piece with attached electrode in position against the diaphragm in the
frame or case of the instrument.
6. The herein described improvement in constructing telephone transmitters
having a diaphragm resting upon an elastic seat consisting in subjecting the
diaphragm and said elastic seat together to the determinate measured pressure of a
weight, spring, or other device, and cementing and rigidly fixing or setting the

page_text: diaphragm in position while the pressure is maintained at the measured or
determined amount.
..
1
100
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.