Improvements in Transmitting and Receiving Sounds by Telephony.
Year: 1897

page_text: Date of Application, 3rd Aug., 1897--Accepted, 13th Nov, 1897
COMPLETE SPECIFICATION.
Improvements in Transmitting and Receiving Sounds by Telephony.
I, JOHN WESLEY GIBBONEY, residing at No. 30 Warren Street, in the City of Lynn,
Commonwealth of Massachusetts, 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 :-
My present invention concerns improvements in telephony, and has particular
reference to the utilization of alternating currents for this purpose. It has heretofore
been proposed to employ alternating currents of such low periodicity that the wave
would not affect the telephone receiver or be audible therein; but my present
invention, while utilizing alternating currents, particularly aims to employ those of
audible periodicity; and it consists, first, in an arrangement for polarizing the cores
of the magnets of the receiving telephones so that a soft iron core may be used
instead of a permanent magnet core, thus saving expense in manufacture. It further
consists in a novel arrangement of a receiving telephone in such a system whereby
alternating or varying currents of a period or rate of alternation such as would
ordinarily produce audible and annoying acoustic vibrations in the receiver apparatus,
may be employed to operate the transmitters, receivers, and signalling apparatus, and
which currents, used in accordance with the improvements herein described, will
produce no noise, or, at the most, will have an inappreciable or insignificant influence
upon the telephone receivers, and therefore do not interfere with the transmission of
speech. In operating by the system of inaudible vibrations, difficulty has arisen in
using alternating waves of a period below audibility, as such waves do not produce a
continuous effect upon the receiver, and the speech waves are therefore transmitted
with a small loss of continuity at times. Although it is possible to operate
commercially a system by the methods pointed out, yet I prefer the method and
apparatus of the present invention, inasmuch as by this the difficulty just pointed
out is overcome.
My invention also consists in improvements in transmitters and receivers,
signalling apparatus, etc., operating by alternating currents in whole or in part,
embodying certain novel arrangements of circuits and constructions peculiarly
adapted for use in an alternating current system of telephony.
A further development of my invention consists in a method of telephoning by
polyphase alternating currents in contradistinction to the use of the single-phase
alternating current such as has been used, and the application of which has just
been described; the object being to obtain a smooth and continuous transmission of
speech of substantially the same equality as that obtained in the use of ordinary
battery arrangements. In embodying the invention I prefer to make use of two-
phase alternating currents, although currents of other numbers of phases could be
readily applied by suitable modifications of mechanism which would be manifest to
those skilled in the art from a study of this specification. The two-phase currents
may be either audible or inaudible in period, and they may differ in phase by just
such an amount as would cause the overlapping of the current waves in the receiver,
and thus obtain continuity of speech, or they may be opposed in phase so that where
the receiver is, as I prefer, differentially wound, the two primary or main currents
neutralize each other and no magnetizing effect is produced upon the core of the

page_text: receiver, except such as due to the vocal or other sound vibrations superimposed
upon or modifying one or the other of the currents. This latter is the preferred
form of my invention, as by it I reduce the necessary wiring to the lowest amount;
and this arrangement can be carried out whether or not the rates of alternation
produce audible vibrations in telephone receivers.
In the method as thus briefly outlined, polyphase currents are ordinarily generated
at a single central station and distributed over a large system by the suitable
switchboards and other appliances commonly used to affect the interchange of
communications. This branch of my invention is not however limited to this form
of apparatus, but I may employ in the central station apparatus using only a single
line and depending upon the earth return, or using a complete metallic circuit; and
in this case I provide a proper phase-splitting device in the subscribers' station.
This ordinarily would be the most economical arrangement, as it would embrace only
a single line of communication with the central station.
Where I use here the term "phase-splitting device," I refer to any of the
well-known methods used in the art for obtaining from a single-phase current
polyphase alternating waves, and this whether the polyphase currents be of two or three
or any other number of phases. Various combinations of resistance, inductance and
capacity in any convenient forms for ready application to my improved system may
be used for the purpose described. I have illustrated several different ways of
carrying this part of my invention into effect, but nothing in the description or
claims hereto annexed is to be taken as limiting me in this regard, as the essence
of my invention consists not so much in particular apparatus (although some forms
thereof are described as well adapted to the invention), as in the combinations
by which I am enabled to employ polyphase alternating currents for the transmission
of speech; at the same time preserving a smooth and continuous effect in the
receivers, overcoming the annoying pulsations due to ordinary variations of current
in telphone lines as commonly constructed, and enabling me to derive the
advantages incident to the use of alternating current in systems of distribution.
So far as I am aware I am the first to employ this class of currents for the purposes
described, and believe myself to be entitled to claims covering broadly not only the
improvement in the art of transmitting sound electrically which consists in so
employing polyphase currents, but also the combinations of apparatus which I have
devised for carrying these improved methods into practical use.
My invention is illustrated in the accompanying drawings, wherein
Fig. 1 shows a suitable generator for supplying the alternating currents used
in the system.
Fig. 2 shows the circuit connections for the field-magnet of the same.
Fig. 3 shows a telephone circuit including the generator and two connected sub-
scribers' stations, together with a novel arrangement of receiver and transmitter
forming a part of the present invention;
Fig. 4 shows the field-magnet of the generator, Fig. 3;
Fig. 5 shows the character of the currents used in the system;
Figs. 6 and 7 show improvements in the calling bell or signal at a subscribers'
station, and a convenient way of obtaining the currents suitable for the subscriber's
transmitting and receiving apparatus.
Fig. 8 shows diagrammatically my improved method of operating receivers when
the alternating currents are of rather high period or of audible period, and shows how
their effects are eliminated in the receiver.
Fig. 9 illustrates a useful arrangement of the receiver and transmitter operating
on an alternating current system, connected relatively as in Fig. 3, and also certain
improvements in the receiver itself adapting it for use with alternating currents.
Fig. 10 shows a modification of the circuits for obtaining the high potential
currents required for an electro-static transmitter ;
Figs. 11 and 12 show improved electro-static transmitters for use in the system;
Fig. 13 is a central station apparatus enfploying two-phase currents on the three-
wire system.

page_text: more particularly adapted for those of inaudible period;
Fig. 18 is a diagram of the current waves as employed in Fig. 17;
Fig. 19 is a diagram of three-phase apparatus;
Fig. 20 is a diagram illustrating a single-phase transmission with phase-splitting
devices in the transmitter ;
Fig. 21 is a modification of the arrangement shown in Fig. 20, with a different
form of transmitter;
Figs. 22 and 23 are other modifications; and
Fig. 24 is a three-phase apparatus with a single line for transmission.
In
In Fig. 1 A represents a Gramme ring armature entirely covered with its winding
of coils and having two leads a, b taken out at opposite points. This armature is
preferably stationary, and inside thereof there revolves a field-magnet F. The coils
of the field-magnet F may receive current from any suitable source, as a battery E,
Fig. 2, or from a separate exciter or a commuted portion of the current from the
winding A. In any case I prefer to avoid the use of collector rings and brushes to
lead the current to the coil upon F, as variations of contact between the brushes
and ring are apt to cause variations of current and magnetic effect in F which may be
reflected more or less into the armature circuit inductively. Instead I may employ
mercury cups at either end of the shaft, dipping or projecting into which mercury is a
prolonged end of the shaft; or the mercury cups may be situated both at one end of
the shaft. In the first case the shaft is made in two parts bound together with inter-
vening insulation, and between these two parts the field coils of F are connected. A
simple contact spring might of course be used instead of the mercury cups.
this way the current is maintained perfectly constant. Instead of the battery E
I can also employ, and in fact prefer to employ where possible, a small separately
running exciter dynamo, having a commutator, and to prevent the fluctuations of
current produced when the brushes pass from segment to segment on the commutator
being reflected into the armature circuit, I place in the circuit between the exciter
dynamo and the field Fa self-induction coil of relatively large amount or value which
smooths out such fluctuations and maintains the current steady; in addition thereto
I prefer to place in shunt to the terminals of the field F a polarization cell which
also tends to eliminate the fluctuations of current in the exciter circuit. Of course
a permanent magnet, if it be sufficiently powerful, may be used as shown in Fig. 3
and Fig. 4, but as the speed of the generator is necessarily low, on account of the
low periodicity of current employed, the former arrangement is preferred as being
more powerful and increasing the capacity of the generator.
The character of the main generated current is that of the main outline of the
wave in Fig. 5, namely, that of a sine wave, while the shape of the wave in its modified
form, as produced by speaking into a transmitter, is roughly indicated by the smaller
waves superimposed upon the main wave.
In former descriptions such as shewn in British Patent No. 13989 dated 2nd August
1892 I have used a transformer whose primary coil is included in the main circuit
and whose secondary winding is closed through any suitable form of transmitter. I
am able to dispense with this transformer altogether, as the core of the receiving
telephone may be used instead and save an extra piece of apparatus and the extra
resistance and self-induction-thereby introduced in the circuit. To make such use
of the receiver magnet core, it is only necessary to provide thereon a local modifying
circuit including the transmitter. Thus, in Fig. 3 the magnet core of the receiver
R has two windings upon it, one a fine winding in the main line circuit, and the other
a coarser winding including the transmitter T. The latter constitutes a closed circuited
secondary around the core of the receiver R and therefore varies the main or
principal current, in accordance with the current which is induced in such secondary
circuit. The resistance of this circuit varies with the resistance of the contact,
self-induction, or static charge, of the transmitter T, and therefore if the diaphragm

page_text: of the transmitter be spoken against, the main wave will be inductively modified, and
will have superimposed upon it much quicker waves or undulations corresponding to
the acoustic vibrations or the movements of the diaphragm; these vibrations are
reproduced in any suitable receiver included in the circuit. The main alternating
wave is represented by the larger sinuous line in Fig. 5, and in its form as modified
by the acoustic vibrations by the smaller transverse waves superimposed thereon; it
being understood of course that the representation of the current corresponding to
the sound waves is not accurate, but merely explanatory. This matter is, however,
readily understood by those skilled in the art. The receiver R', in Fig. 3, has its
local circuit arranged somewhat differently from that of R, but it operates upon the
same principle of changing the inductive effects by varying the resistance in a closed
circuit, this circuit including a transmitter. In this case the receiver magnet core
has but one winding and the transmitter is adapted to shunt a part of the current
passing through all or some of the coils.
The action is, of course, to vary the inductive effects as before, by diverting a
portion of the main current from some or all of the coils upon the core of the
receiver R¹, and the arrangement is the equivalent of that of the receiver R. ..If. the
transmitter T were one adapted for currents of low potential relatively, it would
be necessary usually to place it in a secondary circuit of coarser winding than that of
the main circuit, and this is shown in Figs. 6 and 7. The main line leading from
the station, and including a connected subscriber's station, is shown at c, d. It leads
to two binding posts P, P1, (Fig. 7), and then to a primary coil of a transformer, the
secondary coils of which go to the binding posts S, S¹. The secondary circuit passes
to the telephone receiver R and transmitter. An ordinary carbon transmitter which
is adapted for currents of low voltage may be used with advantage, and be placed in
shunt to all or some of the coils upon the receiver R. This affords a simple
construction of apparatus. The transformer for, accomplishing the reduction of
potential in the main alternating current need not have a special winding, as the
winding upon the magnet which operates the calling bell may also be the primary
winding of such transformer. Thus E represents a core of laminated iron sheets of
soft iron having three legs, surrounding the middle one of which is the winding.
Outside the whole is a permanent magnet with its poles arranged to polarize the
armature A1, pivoted at its centre upon a prolongation of the middle leg of the core
of the transformer, and carrying the bell hammer. When the calling currents, or
currents of extra strength are sent through the primary coil P2, the ends of the
armature become alternately of opposite polarity and are successively attracted and
repelled from the permanent magnet in the usual manner in a rapid vibratorý
movement. The ordinary line current, or what may be called the initial working
current, is not powerful enough to affect the armature, while the fluctuations of the
main wave representing the acoustic vibrations are efficiently transmitted by induction
to the local circuit..
In Fig. 8 is shown that part of my invention which enables alternating currents
having a higher frequency than those which have been heretofore employed to be
used in the operation of a system of telephony in accordance with the principles set
out. Such higher period currents could not usually be employed, on account of the
fact that they would produce an audible tone in the receiver and interfere with
speech; but by the construction illustrated diagrammatically in this figure it will
be shown that the effects of the main current can be entirely or almost eliminated in
the receiver while it may still be used to operate the system. P is the primary winding
.coming from the central exchange, and S a secondary winding wound upon a suitable
iron core, and this core may be, if desired, the core of the magnet which operates
the calling bell, as in Fig. 7. The circuit from the coil S is branched, one part
going through a self-induction coil I of considerable amount and the conductor e, to
the receiver R, and the other branch going thereto by the conductor c, having no
induction coil, but having, preferably, a resistance Re, equal in amount to the ohmic
resistance of the coil upon the core I.. The return conductor d may include a
transmitter T. The magnetizing effects of the coils of wire between c-d and e-d

page_text: are opposed so that any current passing equally from the coil S through c, e will
have little or no influence upon the diaphragm of the receiver. If now, with a
proper selection of inductance at I, and a balancing of the effect of the coils upon R,
alternating currents of comparatively low frequency be passed through the coil P, as
coming from a central exchange, the secondary currents induced in $ pass almost
equally by way of the conductors c, d, and will therefore, as explained, have little
or no effect in producing audible tones in the receiver, but the variations or
undulations of current corresponding to acoustic vibrations at any transmitter will
be of much higher frequency and will meet a large opposition at the coil; they will
therefore pass inainly by way of conductor c, and will affect the receiver diaphragm.
Instead of employing a resistance Re, to balance the resistance of the coils upon the
core I, the resistance of the circuit S, c, d may of course be selected to equal that
of S, I, e, d. There will occur with this arrangement of circuits a slight lagging
effect upon the main alternating current wave flowing through the coil I, and there
will be therefore movements of the receiver diaphragm corresponding to the resultant
magnetizing influence of the two currents, or divided current, passing by the
conductors c and e, but the amplitude of vibration of the diaphragm will be so largely
reduced that alternating currents of quite high frequency may now be used without
annoyance or interference with speech occasioned thereby, as is evident. It is, of
course, also evident that the variations of current produced by the transmitter T will
now occur mainly in the circuits S, c, d.
In Fig. 9 I illustrate a complete telephone instrument, having the receiver and
transmitter combined in portable form, and adapted to operate upon the alternating
current system, as shown in Figs. 3 and 6. The telephone receiver has two sets of
coils, as before, one included between the line electrodes or terminals a, b, and the
other leading along the handle of the instrument to the transmitter, which modifies
the main current, or, as it were, allows only the current from the generator at the
central station to flow through the connected subscribers' circuits as an alternating
current having impressed thereon smaller variations corresponding to the sounds
received by the transmitters; the transmitters acting to vary the apparent resistance
of the circuit, as already explained. The iron core of the receiver is composed of
laminated iron so as to permit quick changes of magnetic condition, avoiding
hysteresis. P is the primary winding or coil connected between the line
terminals a, b and a secondary of coarser wire S leads to the transmitter T. The
iron of the receiver consists of an outer cup which may be formed by a punch and
die, and may consist of several pieces lying one within the other, and an inner core
piece L, also built up, preferably, of laminae, or both may be made of very soft iron,
although the laminated structure is of course the best. The inner core has secured
to it, as by dove-tailing, an extension of solid metal which is screw-threaded so that
the inner core may be advanced towards or retracted from the diaphragm for the
usual adjustment. It will be seen that the magnetic circuit is almost closed and
therefore the receiver is a very efficient transformer. It is of course evident that
instead of using a fine wire primary and a coarse wire secondary upon the
receiver, as shown, there may be employed but one coil connected as shown in
Figa. 6, 7, 8 and 10.
In former descriptions as in the prior British Patent herein before referred to I
have shown that I can transform the work current from the generator at the central
station by step-up transformers, so that electrostatic transmitters may be employed.
I show in Fig. 10 an arrangement of the circuits adapted therefor, and which may
be regarded as a modification of the arrangement of Figs. 6 and 7. The core K
may be the core of the bell magnet, as in Fig. 7, and the main circuit pass
through a part P thereof between the lines a, b. The receiver R is then connected
through all of the winding upon the core K, that is, through P and P¹, and will
therefore be supplied with current of a potential depending upon the relative
number of turns in P and P¹. The receiver R is likewise wound in two
sections P2, P3, one section only, as P2, being connected through P, P¹, while the
electro-static transmitter T is connected through both windings P2, P³, and is

page_text: therefore supplied with currents having a very high potential, because of this
double transformation upwards. The transmitter T will operate efficiently if
constructed as shown in Fig. 11. It consists of numbers of thin laminae of
conductor connected in multiple to one side of the circuit, opposed (with a free air
space intervening) to a number of other plates connected to the opposite pole or
conductor of the circuit, the latter plates being of thicker material so as to have
considerable rigidity, or being backed with a stiffening material, and the former
being made quite thin and flexible so as to respond readily to the vibrations of air
produced by sounds. The thin laminae are indicated at 1, 1, 1, 1, &c., and the
thicker laminae, or rigidly held laminae, at 11, 1, 11, &c. Between one side of a
thick lamina and the side of the adjacent thin lamina is interposed an insulating
separating ring, 8, 8, 8, &c., which is corrugated as shown, or has numerous openings
through it to permit the free entrance of air. Between the other side of the heavy
lamina and the adjacent side of the thin lamina are other insulating separating
rings r,,, &c., and these latter are solid, so as to entirely close in the space
between the laminae. All of the thin laminae are connected, as by a conductor m,
to one side of the circuit, as at P1, and all of the heavier laminae by a conductor n,
to the other side of the circuit at P. This construction enables all the thin
condenser sheets to move in free air towards the sheet of opposite polarity, the air
having access to one side thereof only, while the capacity of all the thin sheets,
acting in multiple, is utilized. A heavy lamina is located at the top, near to the
mouthpiece, preferably, so that the transmitter cannot be injured by objects passed
in through the opening by maliciously disposed or inquisitive persons.
In Fig. 12 the arrangement just described is somewhat modified, so that the
condenser can be used both as a transmitter and receiver. All of the condenser sheets
are made thin and flexible in this case, and are separated by insulating separating
rings so that the sheets are sustained at a slight distance apart. Openings are
provided in these rings so that one side of each positive plate and the opposite side
of each negative plate have free air communication to the ear while the adjacent sides
of each positive and negative plate have similarly free communication with a mouth-
piece V, Fig. 9; it being understood that the terms "positive" and "negative" are
used in the ordinary signification with reference to the charged plates, as, of course,
the charge in the present case would be changing with changes of current. By this
arrangement the alternating current having been suitably transformed upward to a
very high potential, changes in the capacity of the sheets as they move towards and
from each other when words are spoken into the mouth piece V are reflected into the
principal circuit as shown in the previous figures; while the variations of the
principal current produced by the distant transmitter cause a bodily movement of
such sheets by electro-static attractions and repulsions and thus set up sonorous
vibrations in the air and repeat the sounds from the distant transmitter.
In the case of the construction, Fig. 9, in which the entire magnetic structure of
the receiver is made of laminated iron, the polarization of the core which is necessary
to prevent the raising of the pitch to the octave is accomplished by the main or
principal current itself, which may be lowered in frequency until it is no longer heard
in the receiver.
In Fig. 13, A is an alternating current generator having two windings disposed so as
to deliver alternating currents differing in phase by 1800. I have illustrated a winding
like that of the Gramme ring, divided into two parts communicating with the bus-
bars or main conductors a, b of the station. The usual switching and connecting
devices are employed, and are not illustrated, as they form no part of the present
invention. I have indicated at 12, 13, 14, &c., connections to the switchboard, but as
all these details may be indefinitely varied, I do not illustrate them in full. I prefer
a permanent magnet for the field-magnet of the generator, although for this I may
substitute a wound field-magnet supplied preferably from a storage battery, thus
giving the smoothness of current best adapted for telephone work. The permanent
magnet field is indicated at N, S. The generator has the common junction of the
two opposed windings connected to ground at E, and shunting the machine is a

page_text: condenser C so arranged that the self-induction of the generator may be avoided.
Lines, lead from the generator, and their common termination is grounded at E¹;
the current in the line is of phase 180° displaced from that in the line 11. The
line is carried through windings up on the receivers R, R¹, but does not include the
transmitters; the line is carried through other windings upon the receivers, but
also passes through the fine wire windings P of the transformers T, T¹. The
windings S, S of the transmitters form closed circuits with microphone contacts m, m
and diaphragms M, M¹.
The operation of the system illustrated in Fig. 13 is as follows: the phase relation
of the currents in the two lines being at 180° displacement or in direct opposition,
there is no audible effect in the receivers from the principal currents, their magnet-
izing effects in the coils w, w² being equal and opposed. If, however, speech be
uttered against the diaphragms M, M¹ of the transmitters, or any other sound be
communicated to them, the current in the line has inductively superimposed upon
it the vibrations caused by the action of the coil S as a transformer primary; these
vibrations are carried to the coils w, w¹ upon the receivers R, R¹, and there cause
corresponding vibrations in the diaphragms 0, 01 of these receivers.
i
The relation of the line currents is illustrated in Figs. 14, 15 and 16. In Fig. 14
the upper curve represents the energy transmitted through the line 1, the lower one
that through the line ; these two waves are in opposition. When, however, sounds
are produced before the transmitters, the higher frequency speech waves are
superimposed upon the wave of current in the line 1, as illustrated in Fig. 15, and
by it are carried along to the receivers R, R¹. At this point the two coils w, w¹ come
into play; the magnetizing effect of the two being equal, and (by reason of the
phase displacement) opposite, the two fundamental currents are wiped out in the
receiver, only the speech vibrations represented by the broken line in Fig. 10 being
left to affect the diaphragms 0, 0¹.
With the arrangements pointed out it will be evident that the circuit for speech'
actually comprises a metallic line and an earth return; but the effect is as though an
entire metallic circuit were used, it being evident that for all extraneous induction
and leakage currents, the two lines and act in parallel as a single circuit in
connection with the earth circuit; but all these exterior currents pass through the
two windings w, w' upon the receiver, and therefore their effect is neutralized; it
being manifest that in practice only those current fluctuations which pass through
one coil alone of the receivers can affect the diaphragms 0, 0¹ to a sufficient extent to
be audible. At C I indicate in dotted lines a sinall condenser which may be employed
if desired to neutralize the difference in inductance between the lines, caused by
including the transmitter secondaries in one only of these lines. A balancing
artificial inductance in the other line (similarly indicated at 12)'might be used for the
same purpose.
Referring now to Fig. 17, I illustrate a different arrangement of apparatus,
although operating upon substantially the same principles; it being assumed that
the system shown in this figure, which also is operated by two-phase currents, is
adapted for inaudible periods or rates of alternation of the currents, while that in
Fig. 13 would be adapted for either audible or inaudible alternations. As before, A
is the generator delivering two currents, which may have any desired phase relation,
both passing through the lines l, as before, and returning by the earth. It may be
assumed that the currents are 90° out of phase, and their relation would be illustrated
by the two sine waves shown in Fig. 18; but as they are to be primarily inaudible in
character, the exact phase relation is immaterial so long as one current is rapidly
changing in value while the other is not. In this case however I employ a modified'
form of transmitter which I believe to be new with me. The transformer portion of
the transmitter is made in two parts; that is, there are two magnetic cores each
having a winding connected in one or the other of the lines l, l, and a divided
circuit in the transmitter closed through the microphone contacts, the two circuits
being in inductive relation to the coils included respectively in the lines 1, 11. In
the transmitter T the microphone contacts m are in series, but in the transmitter T¹

page_text: these contacts are in multiple; in each case the circuits to the microphone contacts.
from the primary coils of the transformers are substantially independent, at least to.
such an extent that no compound wave would be formed in the microphone to give a
pulsating or fluttering effect in. the receiver.
-
1.
Fig. 19 shows an arrangement employed with three-phase apparatus. It is not the
preferred system, as it introduces several difficulties, a general complication of
apparatus, and multiplicity of circuits both in the apparatus and exterior thereto,
and also necessitates special arrangements for getting a proper magnetizing effect in
transmitters and receivers, it being known that this effect with three currents
differing by 120° is zero; but as the combination of apparatus embraces the same
principles, it is illustrated as a modification of the main idea in my invention..
A is, as before, a generating source, represented as a Y-wound three-phrase
armature, the field-magnet (of any forin or type) not. being represented.
Lines,, lead therefrom and include in their respective circuits to a common
point K the coils w, w¹, w², w³ of receivers R, R¹; in one of the circuits are placed
transmitters T, T which may be of common form, and are represented as working
most conveniently by transformation. The coils w, w¹; &c. are shunted by
condensers, C, C¹, &c., connected between the mains 1, 11, 12, they being of selected
capacity, substantially transparent (employing a term commonly used) to speech
waves. The condenser C is arranged in series with the coil w³ upon the receiver,
the same arrangement being shown in the receiver R¹, the condenser C² and the
coil w forming a shunt around the coil w². The resultant magnetizing effect of
the three coils in the three-phase system being zero, no sound will be heard in the
receiver with any periodicity of alternation, provided the currents be equal; but if
one or two of the circuits be differently influenced, then the receivers will be
correspondingly affected. If the transmitters T, T₁ be operated, the speech waves
will be conveyed to the receivers R, R¹, when the current undulations affect but
one or two of the receiver coils. The coils w², w³ are therefore wound differentially,
the circuit through w³ being by way of the condenser C2, of such capacity as will
readily pass voice current vibrations, and yet suppress the main fundamental waves
from the alternating current source. The circuit for voice currents is thus from T in
parallel by way of w², and w³, C2, the latter two in series (the coil w³ being given
sufficiently increased inductance to balance the capacity reactance of the condenser,
the parallel circuits thus producing no effect in the receivers), through the
condensers C, C¹ to the receiver coils w, w¹. By these latter coils the receiver is
magnetized and responds to the speech waves. As shown in dotted lines, one of the
circuits might be an earth circuit, but this is not preferred.
In the practical working of this part of my invention it is not necessary that
polyphase currents be primarily generated at a central station and sent out over
several conductors, but the out-of-phase currents may be produced locally at a
subscribers' station by means of inductive coils, condensers, polarization cells, or other
apparatus possessing similar phase-modifying properties. Several arrangements
embodying these principles will now be described.
In Fig. 20 I show a single line conveying single-phase alternating current from
a central station, the line connecting communicating subscribers. A transformer T
has a winding P in the line, and another secondary or winding of coarse wire (for
ordinary microphone working) divided into two parts S, S¹. The circuit of the
section. S is completed through a resistance Q, a pair of microphone contacts and the
middle conductor, while in shunt to the inductance I is a condenser C of definite,
limited and selected capacity, such that it forms a shunt around I practically for
voice currents only. The line is continued through the receiver R and the distant
similar apparatus.
The method of operation of the apparatus shown in the figure is substantially as
follows alternating currents of a period below audibility, or nearly inaudible, being
passed over the line 1, a secondary current is induced in the windings S, S¹; the
current in S' however lags behind that in S, owing to the inductance I. There are
thus fed through the independent circuits which include the transmitter contacts,

page_text: two alternating currents the phase difference of which will depend upon the value of
the inductance. If sounds be produced at the transmitter, there will be
superimposed upon the current flowing in S modifying vibrations corresponding to
the voice vibrations; similar vibrations will also be imposed upon the out-of-phase
current flowing in S. The fundamental. currents, being out of phase, have but
negligible action upon the main line, but the voice currents in S, S¹ are in phase
and reinforcing each other are inductively transferred to the primary P. It may be
noted here that it is the condenser C which renders this working practicable, as the
quick undulations corresponding to speech waves can only pass with difficulty the
inductance I, while the condenser is quite. transparent to them; at the same time
the condenser is of such limited capacity that no material part of the fundamental
wave is affected. As the apparatus illustrated utilizes polyphase currents for the
transmitting instruments, and there are therefore no times when one or the other of
the microphone contacts is without current, continuous speech is heard in the
receivers R.
In Fig. 21 is illustrated a method employing analogous principles, but with some
modification in the apparatus. Here the line l, the transformer, inductance, condenser,.
and multiply contact transmitter are as before; but the circuits are different. The
coil has one path through the resistance Q and a set of microphone contacts, and
another circuit through the inductance I and another set of contacts. These are
illustrated as of the granular carbon or "dust" type, which is well adapted to my
invention, as in its exercise a sort of unison of action in the divided contacts of the
transmitter is desirable; in the type described, this is obtained by the average of a.
practically infinite number of minute contacts in each circuit. The resistance Q is
made to about equal the ohmic resistance of the inductance I; around the
inductance is placed a condenser of definite and limited capacity. In this arrange-
ment, out-of-phase currents for the two transmitters circulate as before, but the main
waves through the resistance. and the inductance produce a compound wave in S.
Speech uttered before the transmitter finds, as before, a current flowing through one
or the other of the microphone divided paths, and the voice currents avoid the
inductance I by passing through the condenser C. It will be seen that in the
arrangement in Figs. 20 and 21, the inductance coils I act as local current generators
at those times when the current in the other branch is reversing, and that the quick
undulations corresponding to speech do not need to transverse the inductance, but
find a ready by-path by way of the condenser shunt provided; the condenser has no
material effect in cutting down the current given out by I, on account of its limited
capacity.
In Fig. 22 I show a further modification in which the primary line is itself divided,
one branch including a transmitter coil T, and the other branch a coil T¹, the circuit
to the latter including an inductance I, shunted by a condenser C. The coils S₁
deliver out-of-phase currents to independent microphone contacts, as before, and the
voice currents from both sources add themselves upon the line and in the receivers R,
&c., the arrangement being practically a reversal of that shown in Fig. 20.
wave.
Fig. 23 shows another arrangement which may be employed when the fundamental
wave is of audible frequency instead of inaudible or only slightly audible as with the
apparatus shown in Figs. 20, 21 and 22. In this instance the receiver is wound with
additional coils whose function it is to wipe out or neutralize the main or fundamental
To obtain this result the main line is divided, one branch going through an
inductance I adapted to cause the current in this branch to lag by 120°; another
branch passes by a condenser C of such capacity as to advance the phase of the current
by 120°, while a third branch includes the primary coil of the transformer. Each of
the circuits includes one of the coils w, w¹, we upon the receiver R, thus obtaining in
the receiver a three-phase current with zero magnetizing effect, as in the case of
Fig. 7; the branches, including the coils-w, P, being alone affected by the voice
currents, speech transmission is rendered possible, while no effect, or only a negligible
A resistance Q is
effect is produced by the fundamental waves of the system.
also included in the condenser branch of the circuit, sufficient in amount to adjust the
B

page_text: resistance of the condenser branch to about equal that of the line branch passing
through the transformer.
In Fig. 24 I show an arrangement somewhat similar to that of Fig. 17. In this
case however the currents in the lines, are displaced by 120°. The receiver also
has an additional reversely wound coil w² receiving current from two coils S², S³ in
inductive relation to the coils P, P¹ included respectively in the lines 1, 1. The result
of this arrangement is to produce a compound wave in the circuits S2, S*, W²,
displaced by 120° from the currents in the other coils, and thus to obtain a three-
phase effect in the receiver R, annulling the effect of the fundamental waves, which
may be audible or inaudible in periodicity.
It believe myself to be the first to employ for telephonic transmission of sounds
an alternating current having a rate of alternation ordinarily audible in a telephone
receiver, by superposing upon such a current the sound vibrations to be transmitted,
and then avoiding the annoying fluctuations of the receiver by neutralizing therein
the main transmitting current, leaving only the superposed vibrations of current to
affect the diaphragm.
It is manifest that the ordinary alternating current is best adapted for this purpose,
and I prefer that to all other forms; but I have spoken throughout my description
and in my claims of a harmonically varying current, meaning by this a current
having a reasonably definite rate of change or periodicity, however this may be
accomplished, as an equivalent of the alternating current which I prefer; I have
mentioned this latter form of electric energy, because manifestly the principles of
my invention permit the use of the same means for neutralizing the effect thereof
upon the receiver as if the ordinary alternating current were employed, and I therefore
consider this within my invention.
It is equally manifest that extensions upon and improvements of the means herein
described would be subordinate to the particular invention set out; and this whether
more than one curtent was used; or only a single alternating current.
In any of the arrangements above described, it is to be understood that the values
given to the inductance, condensers, &c., are so selected or adjusted as to give the
phase relations to the currents which may be desired. This can readily be done in
many ways now well known and understood in the electric art and which are not
specially described or claimed by me.
In addition to the broader aspects of the case set out in my statement of invention,
I believe it to be new with me to employ a divided circuit transmitter, or one
having practically independent parts for current from the transformer coils, and this
I wish to broadly cover.
An advantage arises in the use of the methods herein pointed out, as I can
materially reduce the size and cost of the instruments as compared with those
employing low periodicity, and thereby also lessen inductive disturbances.
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. The improved process for transmitting sounds electrically which consists in
using alternating or periodically changing currents of audible periodicity said currents
being modified by a transmitter so as to reproduce sounds in the receiver while at
the same time the fundamental current is neutralized so as to avoid the production of
annoying noises and vibrations in the receiver.
2. For use with alternating or periodically changing or polyphase currents
a telephone receiver so arranged as to be insensitive to the main current alternations
but sensitive to undulations impressed on the main current by a transmitter and
corresponding with sound vibrations.
.3. A magnetic calling or signalling device wound with two coils adapted to act as
a transformer the line being joined to the primary coil and a transmitter being
included in the secondary circuit.
4. The process of transmitting sounds electrically by the aid of polyphase or

page_text: relatively displaced phase electric currents upon one or more of which currents
electrical vibrations corresponding to the sound waves are impressed by the
transmitter.
5. A telephone receiver having a differentially wound electromagnet whereby it is
rendered insensitive to the periodical variations of the main current.
6. The improved systems of telephony arranged and operating substantially as
described with reference to either of Figures 3, 8, 10, 13, 17 or 19 to 24 of the
accompanying drawings.
Dated this 3rd day of July 1897.
W. P. THOMPSON & Co.,
322 High Holborn, London, W.C., Patent Agents for the Applicant.