Improvements, in Telephone Transmitters.
Year: 1892

page_text: Date of Application, 26th Jan., 1892
Complete Specification Left, 26th Oct., 1892-Accepted, 3rd. Dec., 1592
3-
PROVISIONAL SPECIFICATION.
Improvements, in Telephone Transmitters. .
I, JOSEPH GOFFIN; of 11 Rue Royale, Brussels, in the Kingdom. of Belgium,
Engineer, do hereby declare the nature of this invention to be as follows:-
!
The strength and clearness with which an apparatus transmits the human voice
depending directly on the number of variations which the vibrating diaphragm is
5 susceptible of producing in the telephone current, the attempts to produce these
variations in great number in the current have given rise to the numerous systems
of, microphones which are well known. These systems have given good results as
regards strength, but they very often, leave much to be desired in the way of clear-
ness. This is especially due to the fact that the variations produced in the means
10 included in the circuit for this purpose are not.equal throughout the mass of those
means, the vibrations of the diaphragm not being equal at all the points of its
surface or extent. It is also for this reason that the intermediaries which receive
only the vibrations from the centre of a diaphragm, such as is the case in the
Edison, Blake and other telephones, while leaving perhaps something to be desired
15 as regards the strength give the best results as to the clearness and distinctness
of the voice, because the vibrations which influence the intermediary are always
of the same order, that is to say of the order of those of the centre. Hence multi-
plying in the intermediary only those vibrations of the same order is solving the
problem from the double point of view as regards' both. strength and clearness, and
20 this is the original idea underlying the construction of the new transmitter which
forms the subject of. this invention.
2.
}
Experience has shown that the vibrations of a transmitting diaphragm produced
by any sound have nearly the same intensity in a circle situated' a little outside the
mean region, of the diaphragm towards the circumference as they have at the
25 centre. If under these conditions I arrange an intermediary taking, instead of a
single point of contact at the centre, any suitable. number of points of contact
upon the said circle of the diaphragin, 1 evidently augment the variations of the
same order in the intermediary and consequently in the current which when flowing
transmits the voice with many times more power and. clearness.
.30
It is clear that the power and clearness of a transmitter is directly proportional
"to the number of points of contact which can be suitably established upon the
strongest zone or vibratory circle of a diaphragm with given general conditions.
The principle upon which the new transmitter is based being thus clearly
established it is only necessary to determine the nature of the intermediary
35 which must preferably be employed in order to mark with the greatest clearness
and precision the variations of teusion caused by the vibrations of the diaphragm.
If as in telephones hitherto used I employ pencils of hard carbon elastically
bearing upon the vibratory circle above referred to, and these pencils were
five in number, I should obtain a power and clearness 'five times as great, but
-40 it is known on the other hand that a carbon pencil does not constitute the best,
medium because the variations of density produced in this intermediary are too
´small and consequently the fluctuations of tension"not great enough for absolute
clearness. These facts have induced me to use finely granulated carbon as an
intermediary in the circuit and the notably superior results obtained by this agent
-45 in the Hunnings, Berion and other systems need not be set forth. Only in these
systems the variations produced are not equal for two reasons, the first is that the
cup containing the granular material' covering part or the whole of the surface of
the diaphragm receives in its mass variations of unequal density, because it is
acted upon by different vibratory circles so that the fluctuations of tension of the
i.
A

page_text: current are not distinct and the second is that the granular material sinks or settles
and thus forms in itself layers of unequal density which receives more unequal
compressions by the diaphragm because the surface of the granular material
before the diaphragm is not in contact with the latter at all the points of the
surface so that to the inequalities of density are added irregularities of contact.
These inconveniences can be completely obriated by reducing the diameter of
tbe cup for the granular material to such a proportion that the mass of the
granular material enclosed therein cannot undergo other variations, that is to say
caunot settle and will always be in contact with the diaphragm over the whole of
its extent, that is to say it must remain of a homogeneous nature except as regards
the compressions which the diaphragm transmits to. it. The maximum diameter
evidently depends on the length of the cup. By applying a similar cup containing
always homogeneous granular material to the centre of the diaphragm, for example
in the place of the carbon pencil of a Blake transmitter, supposing the latter
constructed in a manner corresponding to the nature of the intermediary I should
obtain a result vastly superior to the Blake precisely by reason of the special
nature of the intermediary so that we may consider a new fact in telephony the
employment of a cup of granular material of dimensions such that they do not
permit the mass to get out of order from ordinary causes, such as sinking, settling
and the like.
Now by providing the large circle of vibrations of a diaphragm with the greatest
.possible number of similar cups I augment the power and clearness so as to
create a transmitter speaking with a force and a precision leaving nothing to be
desired.
.
I provide therefore a sonorous case to which is screwed à mouth-piece pressing
'a
on the diaphragm in a suitable manner at its circumference. Against this diaphragm
is held, in the interior of the sonorous box or case, a disc of a certain thickness of
metal, carbon or even insulating material such as ebonite. This disc contains the
holes constituting cups for, the granulated carbon with which they are filled and
which are arranged symmetrically around the centre upon the strongest vibratory
circle of the diaphragm. The surface of the disc is insulated from the diaphragm
by a suitable intermediate membrane perforated, opposite the holes in order that
the granulated material shall alone come in contact with the said diaphragm.
On the opposite side of the disc the holes are closed by another metallic
diaphragm having a certain degree of flexibility and placed in direct contact
with the perforated disc. When the latter is made of ebonite the holes are lined
with gilt copper, which linings come in contact with the rear diaphragm also
establishing contact. The disc with the central screw which supports it, is insulated
by a sheath from a screw threaded tube which serves to regulate the apparatus by
a more or less strong pressure exerted by the screw thread in the sonorous case.
The screw threaded case is held by the pressure of a nut which fixes at the same
time one of the wires of the circuit to the sonorous case, whilst the other wire is
connected to the central screw by a second nut; the circuit in which the whole of
the apparatus is included being completed by one or more wires connecting the
front diaphragm to the sonorous case. The gilded metallic rear diaphragm is not
only a good conductor of the current, but by its elasticity it also favours the effect
of the variations produced in the intermediary granular material thus augmenting
still further the power of the apparatus.
Of course this construction is susceptible of numerous variations without affecting
the value of the invention. Thus each hole could be closed separately by a small
disc and all these discs connected with each other by a star sliding upon the
central rod. In like manner the holes themselves, instead of being formed in the
disc, could be small independent metallic caps united upon the central rod by
the medium of a similar star to that herein before mentioned.
From the foregoing it might be thought that if I filled with granular material
a continuous circular groove in a disc which coincided with the vibratory circle
of the diaphragm I should obtain the maximum éffect; but this is not so because

page_text: the same inconveniences of sinking, settling, and irregularities hereinbefore stated
will again recur.
There is no fixed rule as regards the number of holes to be employed
because it will be varied according to the nature of dimensions of each
diaphragm.
Dated this 26th day of January 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Telephone Transmitters.
I JOSEPH GOFFIN, of 11 Rue Royale, Brussels, in the Kingdom of Belgium,
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 has for its object to construct a telephone, in which granular
carbon or similar material is used as a transmitting agent, in such a manner that
the inconveniences of the older apparatus heretofore employed are obviated and
a telephone of the greatest efficiency is produced.
The greatest inconvenience in the telephones heretofore used with a granular
transmitter lies in the fact that the latter is included, in the battery circuit, in a
receptacle insulated, at the edge or circumference between two electrodes, on
the one hand the diaphragm and on the other hand a carbon or metal plate; the
current therefore has to find its way from one electrode to the other through the
granular transmitter, consequently it does not at this point pass with its full
strength from one pole to the other and cannot accentuate the variations as
energetically as if the passage took place with its whole strength. Moreover, the
variations produced in the transmitter by the vibrations of the diaphragm, by
reason of the fact that it does not hear to the whole of its extent against conducting
surfaces, are not all transmitted and the transmitter leaves therefore something to
be desired as regards distinctness.
Now my invention is designed to arrange the transmitter in such a manner that
it is not included at the circumference so as to be insulated between two electrodes,
but, being enclosed in a conducting cover, forms itself one battery-pole and closes
the circuit directly by contact with the second battery pole, the diaphragm.
In the accompanying drawing I have shown how my said invention may be
conveniently and advantageously carried into practice.
Figure 1 is a diagram illustrating the principle of my invention.
Figure 2 represents a longitudinal section, and
Figure 3 a transverse section of a practical form of construction.
In the diagrammatic example the arrangement is shown with only one transmitting
cup B which is insulated at its front edge only by a paper ring from the diaphragm D
bearing against the cup. The diaphragm D of suitable metal is connected with
one pole of the battery S, and the walls of the cup made of conducting material are
connected in a suitable manner with the other pole of the battery. Now the
granular carbon mass K with which the cup is completely filled constitutes the
direct intermediary between the diaphragm D and the conducting walls of the cup
or the two battery poles so that the changes or vibrations produced during the
speaking by the diaphragm in the granular transmitter will all exert their action
upon the current. The voice is now transmitted with the greater strength the less
the energy of the current is weakened in its passage through the transmitter, so
that the variations of the transmitter are accentuated the more the stronger the
current is by itself.
If, as already stated, the transmitter is insulated at the circumference, only a

page_text: fraction of the current will pass through the transmitter only to the granular:
condition of the carbon, inasmuch as the current spreading in all directions cannot
pass through laterally and is for the most part lost. The same inconvenience
occurs when the diameter of the cup B is too large, because then the current
spreading laterally is lost in the transmitter by reason of the incoherent condition
of the latter, to which is added a further inconvenience which consists in that the
granular mass sinks and becomes heterogeneous, so that the variations are also of a
dissimilar nature and the voice is not clearly transmitted.
These inconveniences are remedied in the most effectual manner in the first place,
by making the cup for the reception of the transmitter of conducting material so
that the current entering the transmitter can flow off without hindrance in all
directions through the walls of the cup, and therefore the strength of current is
transmitted by it as completely as practicable, and in the second place by using
dimensions which do not permit of the sinking of the transmitter, or enable a
perfectly automatic regulation to take place during every vibration of the
diaphragm.
In practice for instance cups of from 7 to 8 millimetres in diameter and 15 mille-
metres in length give excellent results. As regards the length of the cups it may
be observed that by it the elasticity of the transmitter becomes greater and the
variations therein are thereby still more accentuated.
This clasticity is moreover increased by the fact that the cups are closed at the
rear end by a spring plate P of conducting material, and the said plate is included in
the circuit both by its contact with the cup itself and by a special contact, so as
not to prevent the passage of the current even if the edge should, by a stronger
vibration transmitted through the intermediary, be bent back a little from the edge
of the cup.
For this reason the said plate is made of metal whilst the cylindrical wall of the
cup consists of carbon and therefore has the same resistance as the transmitter,
whereby a more uniform action of these two factors is obtained than if the wall of
the cup were made of a material which conducts better, such as for example metal.
The action of this perfected telephone may be considerably increased by providing
in lieu of a single cup, a number of cups around the centre upon approximately
the circle of the strongest vibrations, whereby the perfected action of the cup is
multiplied and the strength and clearness of the voice becomes greater.
In this case the cups are in practice drilled around the centre of a carbon disc B
which is closed at the rear with a plate and insulated in front by the sheet of paper
from the diaphragm D, as represented in Figures 2 and 3. The cup disc B is then
held in the centre by the pin T and the latter screwed in a suitable manner to the
part A of the casing, and insulated from the same by closing the circuit on the
diaphragm D, whilst the same is closed on the disc B by means of the pin T with
which also the plate P is in conductive connection. The tube R insulates the pin T
from the other parts of the casing. The form shown is however only given by
way of example, and any other suitable construction may be used for carrying the
said principle into effect. In lieu of boring the cups into a disc they may also
consist of separate carbon tubes which are suitably connected with each other, and
being united upon the pin T can be closed at the rear end by means of one or more
spring metal plates.
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
a cup of
First. In telephones, in which, for influencing the current, granulated carbon is
used as a transmitter, the arrangement of the carbon in a tube or
conducting material so that the granular transmitter is enclosed on its entire
peripheric surface by solid conducting walls included in the circuit, and, forming
one battery pole, closes with its front surface the circuit on the other battery pole,
that is to say the diaphragm.

page_text: Second. In a telephone constructed on the principle characterized by the first
claim, for increasing the elasticity of the granular transmitter, the prolongation of
the cups in accordance with the diameter, and the closing of the same on one side
by means of very clastic membranes P included in the circuit.
Dated this 26th day of October 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.