Improvements in Telephones.
Year: 1896

page_text: Date of Application, 29th Jan., 1896
Complete Specification Left, 23rd Sept., 1896-Accepted, 24th Oct., 1896
PROVISIONAL SPECIFICATION.
[Communicated from abroad by LA SOCIÉTÉ ANONYME POUR LA TRANSMISSION
DE LA FORCE PAR L'ELECTRICITÉ, of 13 Rue Lafayette, Paris, France.]
Improvements in Telephones.
I, JOHN IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the
County of London, Consulting Engineer and Chartered Patent Agent, do hereby
declare the nature of this invention to be as follows:-
If one speaks before a microphone excited by an alternating electric current all
the sounds reproduced by the telephone receiver are affected by beats due to the
variations of the intensity of the exciting current, and the receiver emits a sound
which is higher in pitch the greater the frequency of the alternations.
When this frequency is very great the vocal sounds reproduced are unintelligible.
According to this invention means are provided for rendering them intelligible
when the frequency of alternation is moderate, and sets of transmitters and receivers
are so arranged in combination with alternators that two or more line wires serve
for transmission of many independent messages.
is excited by two distinct currents traversed by alternating currents of like
For this purpose, the microphone
frequency, but of phase displaced by a quarter of a period, and the receiver is
provided with two distinct magnetic circuits acting on one diaphragm plate, these
circuits being such that the coefficient of their mutual induction is nil. These
two magnetic circuits are connected each by a separate conducting line to
the two circuits of the microphone, the currents of which are generated by two
alternators.
In the receiver there is an iron base made up of numerous concentric rings from
which project four longitudinally divided iron cores. Two of these diametrically
opposite are wound with coils connected to the one line wire, and the other two,
also diametrically opposite, are wound with coils connected to the other line wire.
The diaphragm plate is fixed near the polar ends of these four cores.
Instead of two alternating currents displaced in phase, there may be a greater
number relatively displaced, each with its line wire and exciting and receiving
coils.
In order that the same pair or greater number of line wires may serve for
transmitting currents for many sets of telephones, it is only necessary to provide as
many alternators giving currents of different frequencies, each two or more having
suitable phase displacements. In connection with the coupled transmitters and
receivers there are resonators which allow currents of only one frequency to pass
and condensers of suitable capacities.
By the arrangements above described each connected set of transmitters and
receivers is rendered independent of every other set, as words spoken to a
microphone excited by currents of a certain frequency can only be reproduced by
a receiver excited by currents of the same frequency.
Each connected set of connected transmitters and receivers is provided with
a call bell worked by currents of special frequency in each case
Dated this 29th day of January 1896.
ABEL & IMRAY,
Agents for the Applicant.

page_text: 2. The receiver has two distinct magnetic circuits so arranged that the mutual
induction of their magnetising coils is nil, these two magnetic circuits being closed
by one diaphragm, their cores being of soft iron, and the coils are connected
respectively to the two microphone circuits which are connected to an alternator
producing the two phase currents of the required intensity.
Fig. 1 is the elevation of the microphone having the oue circuit communicating
with it at S, and S, and the other by R, and R₂.
Fig. 2 is a plan and Fig. 3 is a section of the receiver, having its diaphragm ab
presented to two magnets s₁ s, and c₁ ce, the cures of which are longitudinally split
and project from an iron base made up of concentric rings. The magnet coils
are so wound that s₁ and s, are of opposite polarity and so are c₁ and c₂, and their
conducting wires pass along the central bore U V.
Fig. 4 is a diagram of the connections. A₁ A, are the circuits of the two
microphones, B₁ B. are the circuits of the two receivers, G is the alternator
producing the two currents of different phase, K, K, are the connections for the
sine circuit, I, I, are the connections for the cosine circuit.
If (t) represent the law of variation of the conductibility of the two
circuits formed on the alternator when the microphone is spoken to, being a
constant and (1) being a function of the time depending on the wirds spoken.
If e sin 2 wt and eo cos 2 wt indicate the electromotive forces developed in
the two circuits by the alternator, aud if the coefficients of self induction in these
are so small in relation to their resistances that they may be neglected then the
intensities in the two circuits are

page_text: The attraction F on the diaphragm of the receiver may be thus expressed
FK (+), (K being a constant depending on the construction of the
instrument) or F = K (c + f (t))³ e² = Ke (C2+2 cf (t) + ƒ (1)³).
This expression is the same as that for the attraction on an ordinary receiver
which is actuated by a microphone excited by a battery. The first term, which is
constant, takes the place of that which expresses the constant attraction due to the
permanent magnetism of the cores.
The second term represents a variable attraction which is greater than the
former and which determines the vibrations of the diaphragm reproducing speech.
The third term represents the attraction which would be developed by the
telephonic currents it the cores had no permanent inagnetism; this term may be
neglected.
Thus there is provided a system capable of reproducing speech like an ordinary
telephonic system, without beats in the transmitted sounds because the exciting
current of one of the microphone circuits is maximum when the other is nil,
and thus there is always a circuit capable of transmitting sounds.
Furthermore, the sum of the attractive forces on the diaphragm developed
by the alternating currents being constant, there is no parasitic sound emitted
by it.
It is, of course, essential that the alternating currents which excite the
microphone and those which magnetise the receiver cores should have equal
frequencies.
Let the connections be as shown in Fig. 5, when an alternator H supplies
alternating two phase currents of frequencies w¹ and intensities j₁ = a sin 2 w¹ t
and a cos 2 to the microphone circuits A, A2, while the receiver
circuits B, B, are supplied from an alternator G with currents of frequency w.
The circuits A, and B₁ and A, B, are connected through condensers T of capacity
sufficiently small to prevent passage of currents of appreciable intensity and of
frequencies and w', but sufficiently large to give free passage to currents having
frequencies of the same order as ordinary microphone currents which may be
assumed to be much greater that the frequencies and w. The law of variation
of resistance in each microphone circuit being as before C+f (t), the differencies
of potential at the extremities of A, and A, are
If psin 2 wt and i, = p cos 2 wt, the intensities of the currents in the
circuits B, B, from the alternator G, then the attraction F on the receiver diagram
must be
F = K(+)+ K (i, + y)² = K{(p² + 2 pm f (t) cos (w-w²) t + m² (f (t))}.
Comparing this expression with that formerly obtained for F, it appears that the
second term which alone serves for reproduction of speech now contains the factor
cos (ww). The diaphragm therefore will not reproduce the sounds directed at
the microphone as they will be affected by (w-w) beats per second.
But generally these are imperceptible, or cease to affect the auditor, their
frequency being less than those of the sounds directed at the microphone.

page_text: It follows that it is possible to employ microphones excited by alternating
currents of ordinary frequencies, on condition that these are made to act on receivers
having cores not permanently inagnetic but magnetised by currents of the same
frequency as those which excite the microphones. If they were of different
frequencies no sounds could be transmitted.
From this may be deduced a multiple telephone system in which the microphones
and the receivers of one converted group are excited by currents of equal frequency
while those of another group have also currents of equal frequency which is
different from that of the currents in the former group. The currents are in each
case two phased, being a sine current on one line and a cosine current on another
line. All the sine currents being of different frequencies can be sent by one line,
and all the cosine currents also by one line, the currents being separated at the
station where they are to be received by means of an electric resonator consisting
of a condenser and a self induction coil.
The currents which excite the microphones act effectively only on the receivers
which are actuated by currents of equal frequency.
igo. spews diagrammatically the arrangement for operating 4 telephone
stations, such that P, and P, can communicate, and at the same time P, and P, but
without interference.
The stations are all connected by the line y for sine currents and the line u v
for cosine currents.
G and H are alternators each producing two-phased currents, G giving frequency w
and H giving frequency w. One of the currents of G connects y to earth
or to the common return lines, the other connects uv to earth or the common
returns.
The circuits of H are similarly connected.
The station P which is for currents of the frequency has two resonators, each
consisting of a coil with coefficient of self induction D₁ and a commutator of
capacity E, these being such that E₁ D₁ = 1
4according to a well known law.
Two circuits through E, D₁ connect xy and u respectively to earth, each
circuit having besides the resonator a receiver B and a microphone A.
Each resonator has a short circuiting shunt interrupted by a condenser of
capacity T allowing microphonic currents to pass but not currents of frequency w
or w', which are always inferior to the microphonic currents. The station P, has
the same arrangements as P.
1
The stations P, and P have like arrangements but their resonators have
coils having self induction coefficient D, and condensers of capacity E, such
that E, D, =
The instruments at the stations P₁ and P, are therefore
operated by currents of frequency w, and those at P, aud P, by currents of
frequency w¹.
4π w
On speaking to the microphone at P, which is excited by a current of
intensity (C+f()) o sin 2 w t, this current traverses the adjoining receiver and
divides into two, the first of which Ce, sin 2 wt traverses the resonator, while the
other(), sin 2 wt having quite a different frequency cannot pass the resonator
but passes by the shunt containing the condenser of capacity T to the sine line ay,
whence its currents pass to earth, these not being capable of reproducing speech
except in the receiver of P, which is excited by the current of frequency w.
Similar action takes place at the other pair of stations, but there is no reason
why the system cannot be extended to 2n stations connected in pairs, each pair
having resonators adapted to a different frequency, the highest of which however
should be small in relation to ordinary microphone frequencies.

page_text: III. CALLS.
For the purpose of calling from one station to the other of the connected pair,
an arrangement such as is shewn in Fig. 7 is adopted. In this there is a call F
which when pressed causes the bell of the connected station to sound, this being of
any suitable construction to be operated by an alternating current of low frequency,
such for instance as the magnetic calls of M. Abdank Abakanowitz.
The alternating currents for operating this call may be produced by a special
alternator, which preferably should give two phased currents traversing the sine
and the cosine lines respectively but their frequency should differ from those for
the telephones. The resonator shewn in Fig. 8 consists of the self induction coil L
and condenser C which allows only the call currents to pass, stopping all others.
This circuit is closed by the hook K, resting on the contact j.
When the connected station calls, an armature descends as indicated by the
arrow in Fig. 7, making contact at l.
The electromagnet of the contact has two coils m and n which when they are
traversed by the microphone and telephone currents of the station cause the contact
at 1 to be broken thus opening the circuit of the call.
When the operator at the connected station calls he does so by depressing his
button F, which puts his resonators in connection with earth, so that they offer
resistances that may be neglected to the passage of the exciting currents of both
stations. Consequently all currents of corresponding frequency sent by the two
lines will close themselves at the first station and will cease to traverse the
connected station. This result ceases on releasing the button F.
In order that the resistance of the coils m and n may not affect the speaking, the
two hooks K, and K, when they rise on removing the receivers from them, short
circuit these coils as shewn.
Fig. 9 shews to an enlarged scale the arrangement of the instrument at the
station.
IV. REMARKS.
1. Although the use of two phased alternating currents has been described, three
phased currents might in like manner be employed with three lines instead of two,
the instruments and their arrangement being suitably modified.
2. Instead of employing alternators to produce currents of sinusoidal form, the
alternating currents might be obtained by introducing into the armature circuits of
the generators, vibrators turned to the desired frequencies.
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. The multiple telephone system herein described with reference to the
drawings.
2. The use in the system above referred to of alternators producing currents of
different phase and of determined frequencies.
3. In each line the arrangement of resonator herein described.
Dated this 23rd day of September 1896.
ABEL & IMRAY,
Agents for the Applicant.