Improvements in Telephone Transmitters.
Year: 1894

page_text: Date of Application, 12th June, 1894-Accepted, 14th July, 1894
COMPLETE SPECIFICATION.
Improvements in Telephone Transmitters.
I, JOHN EDWARD KINGSBURY, of 79 Coleman Street in the City of London,
Manager, (a communication to me from abroad by The Western Electric Company,
of Chicago, Illinois, United States of America,) 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:-
This invention relates to current varying transmitters in which the variable
resistance medium is a mass of finely divided carbon, or other conducting material,
held between two electrodes and more particularly to that class of instrument in
which the said medium is contained in a chamber block, technically known as a
"button."
For the transmission of music as from an orchestra, or from a chorus upon a
theatre stage, it has been found necessary to employ a transmitter so designed that,
while extremely sensitive to sounds originating at some distance from the instru-
ment, it shall at the same time remain uninjured by powerful tones originating in
its immediate vicinity. Transmitters for this class of work must moreover be so
constructed that, while competent to respond perfectly and faithfully to the
relatively feeble tones of such instruments as the violin, they will not be adversely,
or abnormally affected by the sounds produced by more powerful instruments, such
as drums, or brass instruments.
In addition to these requirements, it is also desirable that in the operation of
such a transmitter all tones of its own shall be suppressed so that there shall be no
resonance, or sympathetic vibration of the transmitter as a whole, or any of its
parts.
The object of this invention is to provide a transmitter in which the above
requirements are met.
To this end I employ slate as the material for the casing and side wall of the
variable resistance button, and thereby am enabled to form a button which remains
efficient through a wide range of temperature; and I mount the front or vibratory
electrode of the said button on a supporting dise of fine gauze, and thereby am
enabled to maintain an equal air pressure on both sides of the said electrode.
I also provide a comparatively large vibratory diaphragm of wood and mount
the same in a frame, likewise preferably of wood, which is stiffened and enabled to
preserve its shape by a ring of brass, or other metal, secured thereto. The said
wooden diaphragm is preferably encircled by a rubber band, and is retained in
place by spring pressure much in the same way as is the diaphragm of the well
known Blake transmitter.
In the drawing which accompanies and illustrates this Specification, Figure 1 is
a perspective view of an instrument embodying these features, and meeting the
above stated requirements; and the transmitter is shewn as being in an electric
circuit, including a source of current and a receiving telephone.
Figure 2 is a central cross section of such a transmitter; and Figure 3 is a
detail, showing the outer side of the front, or vibratory electrode, secured to the
flexible gauze disc; and provided at its centre with a bolt whereby it is adapted to
be attached to the diaphragm centre.
Referring to Figure 1 a frame R of wood is stiffened and maintained in shape by
a metal ring R' screwed or otherwise fastened to its back surface; and may be
flared, (as shewn in Figure 2) on one side, and shouldered on the other to form a
ring seat for the diaphragm.
Dis a comparatively large diaphragm of wood, encircled by the rubber band r

page_text: in a manner well understood, and retained in said ring seat by the dampening
springs d, in much the same way that is employed in holding the diaphragm of the
well known Blake transmitter.
I have found a diaphragm baving a diameter of three and one half inches to
operate satisfactorily.
The remaining operative portions of the transmitter are combined in a button of
the same general type as that which is used in the "solid back" transmitter but
differing in some degree structurally, and being mounted in an essentially and
radically different manner.
The external appearance of the button B is indicated by Figure 1, and its
internal parts appear in section in Figure 2. As the transmitter is in the use for
which it is primarily designed subjected to great variations in temperature, due
both to the current employed in its operation and to the heat from the lights
which illuminate the stage, it has been found useful to employ slate as the material
for the containing chamber or button.
•
Accordingly I employ a casing of that material and form in one side thereof the
cavity C to serve as containing chamber for the finely divided conducting material
which serves as a current changer or variable resistance.
Secured to the rear of the chamber C, is the fixed or back electrode
e, which is
conductively united to a metal nipple y, extended through the back of the slate
casing and terminating in a socket pin y².
.
The front, or vibratory electrode f, is secured to the centre of the inner surface
of a flexible or resilient disc g, which in turn, is clamped by a metal ring and
suitable screws to the front edge of the slate casing. Both electrodes are discs of
carbon, but other material such as metal may, if desired, be employed.
Electrodes of brass may for example be used, and should preferably be plated
with gold.
The containing chamber C is thus provided with a circumferential sidewall of
slate, with a rigid and conducting rear wall formed by the fixed electrode and with
an clastic and conducting front wall formed by the vibratory electrode.
The current changing material M is placed within the chamber C, and is a
finely divided or granulated conducting substance; carbonized anthracite being
preferably employed.
In order that the pressure of the air may be equal on both sides of the front
electrode, I form the flexible disc g of extremely fine wire gauze, and between the
under-surface thereof, and the surface of the slate casing to which it is secured,
a very thin washer of porous paper is preferably interposed which serves as a
cushion without materially hindering the sufficient passage of air.
The said gauze disc g supports the front electrode and completely closes the
front of the chamber, retaining the granular conducting material in the said
chamber between the electrodes.
The said disc g is secured to the front electrode by means of a clamping plate p,
on its reverse side which is screwed to a stud g attached to the back of said
electrode, and projecting through the centre of the disc. The stud q, by means of
a small bolt p forming a continuation thereof passing through the centre of the
diaphragm and secured on the outer side thereof by nuts n in a manner well under-
stood, serves also to attach the front electrode and thereby the button B as a whole
to the said diaphragm so as to participate in its vibrations.
A light metal bridge b, mounted by its feet on the diaphragm, spans the back
of the button B and a screw socket c, adjustable by a jam nut C, is carried at its
centre, and delicately supports the socket pin y' of the button as shown.
It will be evident therefore that the compound button B instead of being
immovably secured to the attachment of its casing to rigid frame portions of the
instrument, as is the case in the "solid back" transmitter before mentioned, is
mounted wholly but loosely upon the diaphragm itself, and that the light bridge b
and its socket connection c serve merely to support it in place and to aid in
preserving perfect parallelism of the electrodes.

page_text: The instrument when in use may, as shown, be suspended by a light stirrup s:
from cords or chains or wires S, the said stirrup engaging with hooks, pins or
screws fixed on the frame ring R.
One of the circuit wires, w, is to be connected with the front and the other w³
with the back electrode. Any metal strip, or ribbon a, extending from the metal
clamping plate p to the frame may be used to establish the front electrode con--
nection, while the wire w² may be attached at r to the bridge foot 6* as shown, or,
if preferred, the said wire may be attached, say by soldering, directly to the
nipple y which projects through the back of the button casing.
The said wires w and w² are shown as forming the circuit of a source of current E,.
such as a voltaic battery, which circuit includes the transmitter button B, and a
telephone receiver t.
Considering now the compound button B with reference to its mounting, it is.
evident that the front electrode is rigidly attached by means of nuts to the wooden
diaphragm, while the back electrode rests in its support on the frame and is
comparatively loose.
The results of the operation of the instrument are therefore largely due to the
inertia of the slate casing, and probably to a considerable extent also to the simple
agitation of the granular carbon contained in the button.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. In a telephone transmitter a hollow block of slate or substance equivalent for
the purpose described forming the casing and side walls of the variable resistance
containing chamber, said block containing a fixed electrode at the rear of said
chamber a vibratory electrode mounted and adapted to vibrate within the front.
opening of said chamber, and finely divided conducting material placed within
said chamber and between said electrodes, substantially as described.
2. In a variable resistance button for a transmitting telephone, the combination.
of a hollow block of slate, forming the casing and sidewall of the resistance
containing chamber; a fixed electrode, secured within said chamber, and forming.
its rear wall or floor; a vibratory electrode mounted and adapted to vibrate within.
the front opening of said chamber; finely divided conducting material, placed
within said chamber, and between said electrodes; and a disc of fine wire gauze
supporting the said vibratory electrode, secured to the front. of the casing and
closing the said containing chamber, substantially as specified.
3. The combination in a telephone transmitter of a diaphragm, a variable
resistance button, mounted wholly upon said diaphragm, and a light back support
also mounted on said diaphragm and delicately holding said button in place,
substantially as described.
4. In a telephone transmitter a diaphragm of wood held in place by spring.
pressure only combined with a hollow button mounted thereon, the said button
comprising a block of slate forming the casing and sidewall of a containing.
chamber; a carbon disc secured therein and serving as the fixed electrode;
a vibratory electrode secured to a flexible disc of wire gauze clamped to the front
of said containing chamber, the said electrode being attached also to the centre of
the said wooden diaphragm and adapted to participate in the vibrations thereof
granular conducting material enclosed in said chamber, and a rear support for
said button, substantially as described.
5. A telephone transmitter substantially as described and represented by the
annexed drawings.
J. E. KINGSBURY.