Improvements in and relating to Telephone Transmitters.
Year: 1895

page_text: Date of Application, 28th Dec., 1895-Accepted, 8th Feb., 1896
COMPLETE SPECIFICATION.
Improvements in and relating to Telephone Transmitters.
I, THOMAS JOSEPH RORKE, of 17ª Great George Street, in the County of
Westminster, Electrical Engineer, 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 telephone transmitters and has for its objects improved
constructions of such apparatus by which a large clectric current can be employed
for telephonic purposes without causing disturbing effects in the circuit or injury
to the microphones, and at the same time increasing the efficiency of the
transformer or induction coil. By my invention the transmitter can be utilized
for speaking over very long distances and also over very had lines or over lines
much disturbed by neighbouring wires, which would be impossible if only a weak
current were employed.
According to my invention I construct the telephone transmitter with two,
three or more distinct microphones constructed of metal or carbon rods one or
more of the rods of each microphone being carried by a rigid support and the
remaining rod or rods being secured to a rigid frame carried by or bearing
against a flexible diaphragm. The said frame is preferably secured at one point
only to the diaphragm, but in some instances it is connected to the diaphragm at
more than one point. By this construction all the microphones are actuated
simultaneously and in an exactly similar manner, and all are equally effectual for
speaking purposes. The microphones are connected to separate batteries or other
sources of electricity by distinct circuits, preferably no common return being used.
By constructing the transmitter with several distinct microphones a large current
may be employed.
I am aware that telephone transmitters have already been constructed with two
or more microphones secured at different points on the vibrating diaphragm
which in some cases forms the common electrode for the microphones but such
microphones have not been carried by a rigid frame attached to the diaphragm
which constitutes the essential difference between my invention and the con-
structions heretofore known. Moreover in my improved transmitter the
diaphragm does not act as an electrode for the inicrophones but merely as a
means of mechanically conveying its vibrations to the microphones.
In order that my invention may be clearly understood I will now describe the
same with reference to the accompanying drawings, in which
Figure 1 is a vertical section of my improved transmitter taken on the line
Figure 2.
y
Figure 2 is a horizontal section of the transmitter taken on the line xx
Figure 1.
Figures 3, 4 and 5 are diagrams shewing various methods of connecting the
microphones, as hereinafter fully described.
Figures 6 and 7 are vertical sections of two modifications of my improved
transmitter.
A is the transmitter case, which is shown broken away in the drawings. B. is
the diaphragm which may be made of wood, glass metal or other suitable
[ Price 1

page_text: material. C is a plate of insulating material rigidly secured to the case A. The
said plate extends nearly to, but does not touch, the diaphragm B.; On this plate
are carried split terminals. D, D, by which carbon rods E, E, are carried.
To the diaphragm B is attached, by means of a screw B₁ or in any other
suitable manner, a light, hollow rigid frame F of insulating material in which are
carried pairs of carbon rods G, G'. These latter rods are on a level with the
rods E, E and of each pair of rods G, G¹ oue is on one side of the adjacent rod E
and the other on the other side of the said rod. The three rods G, G¹, E form
a set and the drawing shews a transmitter having three such sets of rods.
Supported upon each set of rods, as shewn in Figures 1 and 2, are balls H, H
of carbon, lead, iron or other suitable material. A set of rods together with the
balls appropriated thereto constitutes one microphone. The transmitter may be
made up of any number of microphones according to the strength of current
that it is desired to pass through the transmitter. The balls when of iron and
lead may be gold-plated or platinized.
The carbon rods are preferably of circular cross section with circumferential
corrugations as shown in Figure 2. The object of these corrugations is to prevent
the balls H, H¹ from rolling or vibrating in the direction of the axis of the rods,
which motion would seriously impair the clear and loud speaking capabilities of
the telephone. The rods may be gold-plated or platinized or they may be made
entirely of metal in which case the balls H, H₁ would be carbon without being
plated or platinized:
It is obvious that the larger number of rods may be arranged on the fixed
plate C instead of on the movable frame F, as herein before described. This
arrangement will enable the frame F to be made very light.
Several methods of connecting my improved transmitter with the batteries and
induction coils are shown diagrammatically in Figures 3, 4 and 5.
Figure 3 shews the connections employed when a separate induction coil is used
for each microphone. J J J are the batteries. K, K are the secondary windings
and L L are the primary windings of the induction coils. It will be noticed
that there are two primary windings L L to each induction coil and therefore, in
this case, to each microphone. Each of the two primary windings of a pair are
so wound and connected in the well-knowu manner that they assist each other in
their action upon their respective secondary winding.
The current enters a microphone at E and there divides, one part passing
through the balls H' to the rod G₁ and thence to the primary L and through the
battery J back to the rod E, and the other part passing from the rod E through
the ball H to the rod G and thence to the primary winding L' and through
the battery J back to the rod E. The current in this way has provided for it
two paths and therefore only half the current has to be carried by each
part; moreover by this arrangement the induction coils are rendered very
efficient.
The operation of the transmitter is as follows: On a person speaking into the
transmitter the diaphragm B is set into vibration which causes the frame F and
with it the rods G G to move. Let us consider the state of things at the instant
when the diaphragm has just moved forward in the direction indicated by the
arrow in Figure 3. It will be seen that the pressure of the rods E and G on the
balls H is less than the pressure of the rods E and G₁ on the balls H. This will
cause a rise of current to take place in the primary winding L and simultaneously
a fall of current to take place in the primary winding L'. On the reverse
movement of the diaphragm the reverse action takes place and therefore the
current falls in the primary winding L and rises in the primary winding L.
It will be understood that with the arrangement hereinbefore described an
exactly similar action takes place simultaneously in all the microphones.
Figure 4 shows the connections when only one induction coil is used for the
whole of the microphones.
L, L' and L' are the primary windings.

page_text: I sometimes use in each microphone only one fixed and one movable rod.
The circuits are then arranged as shown in Figure 5, the primary windings
in this case being all wound in the same direction as in an ordinary induction
coil.
Although I prefer the method of connecting up the microphones shown in the
drawings nevertheless they may also be connected up in parallel as one large
microphone, or separate batteries may be used for each microphone with a common
return in the well-known manner, and in these cases an ordinary induction coil with
one primary and one secondary winding would be used.
The arrangement shown in Figure 6 is one enabling carbon granules to be
utilized instead of the carbon or other balls hereinbefore, described. For this
purpose I prefer to reverse the relative positions of the movable frame F and the
fixed plate C, the latter being arranged above the movable frame F, as shown in
the said Figure 6. In this instance F is a light plate of insulating material on the
upper face of which the rods G G¹ are attached in any suitable manner. The
rods EE are secured to the lower face of the fixed plate C so that each rod E
lies between a pair of rods G, G¹ without touching the plate F. The plate F is
shaped like a tray with insulating partitions F F across the tray between each
microphone so as to insulate the microphones from one another. The spaces
between the rods are loosely filled with carbon granules M which take the place,
in this arrangement, of the carbon, lead or iron balls aforesaid. I find that the
fixed rods E E act most efficiently, in this form of microphone, if they have a
triangular cross section and are corrugated circumferentially.
Although I prefer to attach the movable frame or plate F to the diaphragm B
at one point only, I sometimes attach it to the diaphragm at two or more points.
The said frame or plate is preferably securely attached to the diaphragm Bas
hereinabove described but it may be unattached, in which case it is suspended or
supported in such a manner that it bears against the vibrating diaphragm and so
that it is free to correctly respond to the vibrations of the diaphragm. A con-
venient method of suspension is that shown in Figure 7 in which OO are arms
secured together or formed in one piece and pivotally suspended at O' on an agate
or steel knife edge in a bracket or arm rigidly secured to the case A. The
arms 0,0 are attached to the frame or plate at O2 O2. Rigidly secured to
the said arms OO is a balancing arm Os having at the end remote from the
diaphragm B an adjustable counterpoise weight O* which is moved in and out on
the screw threaded arm 03 in order to adjust the pressure with which the frame
or plate F bears against the diaphragm B. I
to
arrange
may also
the
vary
pressure of the frame F against the diaphragm by means of spring pressure acting
on the arm 03 or at any other suitable part of the suspended frame. A piece of
magnetized steel is preferably secured at F2 where the frame F touches the
diaphragm B, which latter will in this case be of thin sheet steel or iron. The
magnet F2 will cause the frame F to adhere to the diaphragm B and will enable
the said frame to correctly follow the movements of the said diaphragm.
Various other methods of suspension may be adopted for example I may
support the movable frame either from above or below on springs, or I may suspend
it from silk threads or in any other convenient manner.
It is sometimes found advisable to damp the movement of the balls H H¹.
When iron balls are used as hereinbefore described their vibrations may be con-
veniently damped by means of a magnet suitably arranged to act upon the said
balls in the manner well known in other transmitters. The damping of the vibra-
tions of the balls, whatever material they may be made of, may be accomplished
by means of a cotton-wool, felt or other similar pad or damper provided over the
said balls and pressing lightly thereon.
I wish it to be understood that although the transmitter arranged as shown and
described is preferably used with an induction coil, nevertheless on account of the
large total current which can be passed through the transmitter and on account
of the large variations of resistance of the microphones, I may by slight

page_text: alterations in the connections adapt the transmitter to be used without any
induction coil.
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. A telephone transmitter comprising two or more distinct microphones con-
structed of metal or carbon rods one or more of which in each microphone, is
carried by a rigid support the other or others being secured to a rigid frame carried
by or bearing against a flexible diaphragm, with metal or carbon balls resting on
and between them, substantially as described.
2. In a telephone transmitter the employment of gold plated, or platinized balls
of iron, lead, or other suitable material, substantially as described, and for the
purpose specified.
3. A telephone transmitter wherein the movable part of the microphone or
microphones is supported by means of springs, or by silk or other flexible supports,
or by means of a knife edge, substantially as described.
4. In a telephone transmitter of the kind hereinabove described the rods of
circular or triangular cross-section and corrugated circumferentially, substantially
as described and for the purpose, specified.
5. In a telephone transmitter of the kind hereinabove described having gold
plated iron balls, a permanent or electromagnet placed in proximity to the said
balls, substantially as described, and for the purpose specified.
6. The dampers of cotton-wool, felt or other suitable material substantially as,
and for the purpose, specified.
7. A. telephone transmitter constructed substantially as described with reference
to Figures 1 and 2 or to Figure 6, or to Figure 7, of the accompanying drawings
and operating as, and for the purpose, specified.
Dated this 28th day of December 1895.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.