IMPROVE- MENTS IN TRANSMITTING AND REPRODUCING SOUNDS AT A DISTANCE AND IN APPARATUS EMPLOYED THEREIN
Year: 1883

page_text: LETTERS PATENT to Alfred George Brookes of N° 59 Chancery Lane in
the County of Middlesex Patent Agent for an Invention of IMPROVE-
MENTS IN TRANSMITTING AND REPRODUCING SOUNDS AT A DISTANCE AND IN
APPARATUS EMPLOYED
THEREIN communicated to him from abroad by
Theodore N. Vail of Boston in the State of Massachusetts one of the
United States of America
COMPLETE SPECIFICATION filed by the said Alfred George Brookes at the
Office of the Commissioners of Patents on the 18th October 1883.
ALFRED GEORGE BROOKES of N° 59 Chancery Lane in the County of
Middlesex Patent Agent IMPROVEMENTS IN TRANSMITTING AND REPRODUCING
SOUNDS AT A DISTANCE AND IN APPARATUS EMPLOYED THEREIN communicated to
me from abroad by Theodore N. Vail of Boston in the State of Massachusetts one
of the United States of America
This invention relates to the art of transmitting and reproducing articulate
speech at a distance and it consists in an improvement in the said art. It further
consists generally speaking, in a nevel method of producing the undulating pulsa-
tions or currents of electricity which are essential to the successful transmission of
articulate vocal sounds. It further consists in certain instrumentalities and forms
of apparatus in which the said improved method may be embodied, and by means
of which I am enabled to transmit speech with great clearness and facility.
The aim of my invention is to secure such results, and, furthermore, to provide
instruments of an extremely simple and economical construction. Heretofore all
transmitting telephones, so far as I am aware, have based upon certain principles
in electrical and magnetical science, which, as a recognition of the present state of
the art, I will now briefly describe. The first type is that which is now almost
exclusively used as a receiver-id est, the ordinary Bell magneto-telephone, in
which, when used as a transmitter, the undulating currents are developed by the
vibration of a diaphragm of thin sheet iron under the influence of the voice in front
of a magnet, the core of which is surrounded by a helix of fine insulated wire,
forming part of the main-line circuit, in which is also included the helix of the

page_text: receiving-telephone. The said vibrations alternately re-inforce and weaken the
strength of the magnet, and the magnetic variations produced brief magneto-
currents in the transmitting-helix of a character corresponding to the sound waves
resulting from the spoken words, and these vibrations, passing over the main line
and through the helix of the distant receiving-telephone, vary the magnetism of
the same, causing its diaphragm to vibrate synchronously with the transmitting
diaphragm throwing the air into vibrations, thus reproducing the sound. Trans-
mitters of the second type are those in which the action of the voice on the
diaphragm, instead of producing electric currents by creating and varying an
electro-motive force, varies the resistance of a voltaic battery circuit. Undulations
of a much greater magnitude are thus developed with a corresponding strength in
the reproduced tones. The best example of an instrument of this class is the well
known Blake transmitter in which the diaphragm, when vibrated effects a variation
of resistance by varying the degree of contact pressure existing between two
electrodes in the battery-circuit, the said electrodes being normally in slight
contact one with another.
Other instruments of this class have been constructed in which a conductor
forming a part of the battery-circuit dips to a greater or less extent in a conducting
fluid, which also forms part of the circuit, thus producing the necessary variation
in the, current strength My invention, however, is based upon a principle in
electro-dynamics, which, though well known, per se, has not heretofore been
directly utilized in the transmission and reproduction of articulate speech. The
principle may be thus stated: When a conductor or coil of insulated wire through
which an electric current is passing is caused to approach or recede from another
conductor currents of electricity are induced in the latter or secondary conductor
of a strength depending partly on the strength of current flowing in the primary
conductor, partly upon the distance between the two coils, and partly upon the
rate of speed which characterises the approach and recession of the moving coil.
This principle I have embodied in a transmitting telephone consisting of two coils
of insulated wire, one of which conveys a constant electric current, while the other
is included in a main circuit of any desired length, having one or more telephones
inserted therein as receivers. One of the said coils is adapted by suitable devices
to vibrate by the sound waves consequent upon spoken words, while the other coil
is stationary. The movement or vibration of the freely held coil in front of its
fixed counterpart induces alternating currents of an undulatory character in the
secondary coil independent of any variation in the strength of the electric current
flowing through the primary coil. Although for convenience I prefer to vibrate
the primary coil through which the current is flowing and to hold the secondary
or main line coil stationary, such a condition is not essential to the success of my
invention, and I may, without materially affecting the results, reverse that arrange-
ment, should it be desirable so to do. Moreover the presence of an iron, paper, or
other diaphragm is not necessary, although in practice it will be found preferable.
In the usual construction of my transmitter I employ with or for a transmitting
diaphragm a volute or a coil of insulated wire made up of several rows. This
volute coil or helix may be glued or shellaced so as to form a stiff surface of
sufficient extent which will respond readily to the air vibrations produced by the
voice. This coil is fastened firmly to its edge to a suitable standard.
A secondary coil, similar in form but composed of finer wire, and consisting of
a much greater number of convolutions than the first coil, is placed near to but
not quite touching the latter. The ends of the second coil are, when the instru-
ment is to be operated, connected in the circuit of a telephone line which includes
the receiving telephone.
An electric current constant in strength is passed through the first coil. On
speaking near the latter it is caused to vibrate bodily, inducing in the secondary
coil alternating electric currents of an undulatory character, which, passing over
the main line and through the helix of the receiving telephone, cause the
diaphragm thereof to vibrate synchronously with the vibrations of the primary

page_text: or diaphragm coil of the transmitter, thus reproducing the words uttered near the
said transmitter
In the drawings I have shown several forms in which my invention may be
embodied, and also some of the essential parts of the same.
Figure 1. shows the primary or inducing coil detached and connected in the
circuit of a battery: Figure 2, the secondary coil, with its circuit closed, through a
magneto-telephone: Figure 3, a sectional view of the instrument in its simplest
form. Figure 4, shows a slightly modified form, in which both coils are provided
with iron cores extending through their centres. By the use of this form, the
effect of the voltaic induction is augmented by the magneto electric induction
between the two cores and their respective coils. Figure 5 shows an instrument
embodying another modification of the same principle, in which the coils are
pyramidal in form, one of the said coils that which is made convexly pyramidal,
being adapted to project into the other which is concavely pyramidal. Figure 6
is a sectional view of another form, in which the primary coil is fitted loosely
within the secondary coil. Figure 7 represents still another form showing
a combination of my improved method and the apparatus by which it is put in
practice with a magneto telephone. Figure 8 is an enlarged view of the form
shown in Figure 3
In Figure 3, A is the primary coil, supported in clamps 8 attached to the front
of a suitable frame or standard, M which is fitted with a mouthpiece a. The ends
of this coil are united with the poles of a battery, D. In close proximity to the
primary coil I place a secondary coil, B. This is of high resistance, being composed
of a great number of turns of insulated wire.
Connected with its ends, which may be extended to any desired length by being
connected with a main-line circuit, is a telephone T. In front of the primary coil
is an iron diaphragm,f to which the coil is cemented, or fastened otherwise. A plate
of iron, c, is placed behind and close to the secondary coil B. The presence of these
iron plates augments the inductive effect of the coil A upon the secondary coil B.
Figure 8 is nearly the same as Figure 3 and is shown on a larger scale. It
represents the instrument in its simplest form. The iron diaphragm and plate f
and c respectively, are dispensed with. The primary coil A is clamped at its edge
(shown at 8) to the front board of the standard M. The secondary coil is held by
the brace N. An air space, R, is left between the front board and the coil A
The volute or diaphragm coil may consist simply of one row of insulated copper
or iron wire or a coil consisting of several rows, may be employed, as in Figures 5
and 6. Figure 5 shows the primary helix, consisting of several rows wound in a
pyramidal form. The secondary coil B. is pressed in a form corresponding there-
with. In Figure 6. the primary coil loosely fits within the secondary coil B, thus
enabling the primary coil to exert an inductive effect on the edges or flanges of
the secondary coil, as well as on the surface thereof.
In Figure 4 both coils are represented as being fitted with iron cores e and ḍ
which aid in the inductive effects.
In
Figure 7. shows a magneto telephone combined with my charged coil diaphragm
transmitter. f is an iron diaphragm, to which is fastened the inducing coil A,
and which is clamped, as in the foregoing figures to the standard. The secondary
coil B, surrounds the core of a magnet h¹. The iron diaphragm forms a part of
the primary circuit, the primary coil being attached thereto at the point x.
this form of instrument the effect of the vibration of the iron plate in the magnetic
field surrounding the end of the magnet, being inductive, is added to the inductive
action of the coil A on the coil B, causing an increase of volume in the transmitted
speech. When iron wire is used for a primary coil, the coil as a whole is rendered
quite magnetic.
In the ordinary microphonic transmitter the largest amount of current that can
be used to advantage is about one ampere per second.
This is because of the heating of the electrodes at their point of contact. Frying

page_text: and hissing noises ensue when the contact become heated, these interfering with
conversation. What is gained in loudness by an increase of current above the
amount stated is lost in distinctness of articulation. One great advantage of my
invention is that the amount of inducing current employed is limited only by the
burning of the insulating substance surrounding the wire of the coil diaphragm.
With a coil made of moderately large wire very intense currents may be used and
consequently strong inductive effects may be produced. According to the laws of
electro dynamic induction, an induced current is proportional to the square of the
inducing current and as the limit of available current large, very satisfactory
results are obtained
I am aware that heretofore induction coils have been employed in connection
with transmitting telephones: but such use has been entirely subordinate to the
variations of the strength of current passing in the primary coil, caused by varying
the pressure at a point of contact. My invention is distinct from any such use,
since in the primary coil which I employ the current of electricity is of constant
strength, and the currents in the secondary coil, instead of being induced by the
increase and decrease of an electric current, are induced by the approach and
recession of a charged primary coil
I have spoken of the primary coil as being made of iron wire. The secondary
may be made of iron wire also.
I claim.
coil
First. The hereinbefore described method of transmitting articulate speech, which
consists in producing the electrical undulations essential to the said transmission
by vibrating a coil or helix carrying a constant current of electricity in proximity
to a secondary coil or helix forming part of a closed circuit including a receiving
telephone or conversely by vibrating the said secondary coil in proximity to the
current carrying coil.
:
Second. A telephone transmitter, consisting of a coil or volute in a battery
circuit a secondary coil adapted to be included in a line circuit and means for
vibrating in correspondence with articulate vocal utterances one of the said coils
in the immediate proximity of the other, whereby the said articulate vocal
utterances may be reproduced in a receiving telephone included in the circuit of
the secondary coil.
Third. A transmitting telephone consisting of a coil or helix in a battery circuit,
a secondary coil adapted for inclusion in a main line circuit, and a mouthpiece by
which the sound waves of the human voice may be directed to the primary coil
whereby the said primary coil may be vibrated in the presence and vicinity of the
secondary coil as described.
Fourth. A telephone transmitter consisting of a coil or volute in a battery
circuit a suitable frame or support therefor, a secondary coil adapted to be included
in a main line circuit, and a mouth piece by which the sound waves of the human
voice may be directed to the primary coil, may be vibrated in the presence and
vicinity of the secondary coil, as described.
Fifth. In a telephone transmitter, a primary coil in a battery circuit, a diaphragm
attached thereto, and a mouth-piece in front of the said diaphragm, combined with
a secondary helix included in the circuit of a receiving telephone and supported in
inductive proximity to the primary helix substantially as and for the purposes
described.
Sixth. The combination, in a telephone transmitter, of a helix in a battery
circuit and a second helix in a main line circuit, including a receiving telephone,
whereby when either helix is vibrated by vocal utterances in the vicinity of the
other undulatory currents are produced in the secondary helix and the vocal
utterances reproduced in the receiver.
Seventh. The combination of a helix in a closed battery circuit with a secondary
helix, a closed circuit in which the said secondary helix is included, and one or
more receiving telephones, also included with the secondary helix in the closed

page_text: circuit, so that the vibrations of the primary helix shall induce electrical undula-
tions in the secondary helix, substantially as described.
Eighth. In a telephone transmitter, a primary helix or volute in the circuit of a
battery, a diaphragm attached thereto, a supporting frame therefor, and a mouth
piece inserted in the said frame in front of the diaphragm, combined with a bar
magnet placed in inductive proximity to the said diaphragm, and a secondary coil
or helix surrounding the core of the said magnet in inductive proximity to the
primary coil, whereby the inagneto electric currents induced by the action of the
diaphragm on the magnet are superadded to the electro dynamic currents induced
in the secondary coil by the vibration of the primary helix substantially as
described.
In witness whereof I the said Alfred George Brookes have hereunto set my hand
and seal this Seventeenth day of October in the year of our Lord One thousand
eight hundred and eighty three
ALFRED GEORGE BROOKES (L.S.)