IMPROVEMENTS IN TELEPHONIC INSTRUMENTS."
Year: 1882

page_text: LETTERS PATENT to Amos Emerson Dolbear of Somerville, Massachusetts,
United States of America, now of Queen Victoria Street, in the City of
London, for an invention of IMPROVEMENTS IN TELEPHONIC INSTRUMENTS."
$5
PROVISIONAL SPECIFICATION left by the said Amos Emerson Dolbear at
the Office of the Commissioners of Patents on the 6th April 1882.
AMOS EMERSON DOLBEAR, of Somerville, Massachusetts, United States of
America, but now of Queen Victoria Street in the City of London "IMPROVE-
MENTS IN TELEPHONIC INSTRUMENTS
"
My Invention relates to electrical telephonic transmitters and is designed to
afford the means for producing a more advantageous effect of the vibratory action
of the sound waves upon the electrodes of these instruments than has heretofore
been practicable.
Hitherto telephone transmitters have been so constructed that the sound-
vibrations in impinging upon the diaphragm or the electrodes cause the latter to
vary in closeness of contact in the same order as the various phases of the sound-
waves, the condensations in the air-waves increasing the compression, and the
rarefactions diminishing the compression at the terminals where the resistance in
the circuit is varied.
The peculiar and distinctive novel feature of one portion of my present invention
is the arrangement of the parts of the instrument in such a relative position that
the above conditions are reversed, that is to say, the sound vibrations in the air
will so act as to cause the greatest separation of the electrodes at that phase at
which, in the former instruments, there is the greatest compactness.
If two suitable electrodes through which a current of electricity is passing are
so adjusted that one or both shall be capable of being freely moved by sound-
vibrations, and such sound-vibrations are so directed as to act between the
electrodes instead of upon the outer surface of one of them, then the condensations
will tend to make them separate and the counteracting force which may be either
their weight or a spring, or other means will make them return to their norma!

page_text: position and pressure, while the rarefactions will cause the terminals to press upon
each other more strongly as the air-pressure between the electrodes will be less than
that external to 'them."
For example I may employ a short tube containing two electrodes formed of
thin metal of a width nearly equal to the diameter of the said tube and extending
longitudinally from the end at which they are fixed to the other end of the same.
Each of these electrodes is capable of slight movement towards and away from the
other, and both are in connection with wires or conductors from any source of
electricity. If sound-vibrations enter the tube at the end at which the electrodes
are fixed, the condensations of the air will tend to force their free ends or terminals
apart.
In another form or modification of my invention one electrode only is capable of
movement, the other being fixed on a suitable base The parts should be so
enclosed in a box or case as to prevent the escape of the sound-vibrations that enter
it otherwise than by passing between the electrodes.
In another example or modification of the said instrument I employ a short
cylinder or ring to the opposite flat sides of which I attach two diaphragms or
plates; these plates may be of metal and the electrodes are fastened to them in
such a manner that their terminals meet in the centre of the cylinder. I form
in the said cylinder two diametrically opposite holes or apertures:
Any sound
vibrations entering one of these apertures will act upon the plates in the manner
above specified that is to say, they will cause them to vibrate in phases exactly
the reverse of those in which either would vibrate if acted upon externally and
perpendicularly to them.
From the above description it will be obvious that with these improved instru-
ments the current will be varied in the same order as the vibrations of the voice
or other source of sound but the phases of the sounds will be completely reversed.
According to another part of my invention I construct the transmitter as
follows, that is to say, I provide a tube formed of thin metal or other suitable
material and of convenient form for speaking into one end of the same.. The other
end may be either open or closed. Near this end of the tube (but sufficiently.
distant therefrom to permit the same to vibrate freely from the effect of the sound)
I surround the same with a carbon ring. The said ring should fit closely but not
tightly on the said tube. It may be formed of solid hard carbon, or of this material
in a granulated or powdered condition. In the latter case I prefer to place on the
end of the tube a cup-shaped piece formed of wood; ebonite, or other suitable
insulating material and to form in the same a circular groove or channel for con-
taining the carbon. The space at the sides of the carbon within the cup should be
packed with felt or the like to prevent the displacement of the carbon. One wire
of the circuit is in electrical contact with the outer surface of the carbon ring and
the other is in contact with its inner surface; this contact may be obtained by
making the tube of metal and having a common, binding screw affixed to it. When
the sound enters the open end of the tube the vibration's produced thereby upon
the carbon ring will cause the required variations in the current.

page_text: .
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Amos Emerson Dolbear in the Great Seal Patent Office on the
6th October 1882.
AMOS EMERSON DOLBEAR, of Somerville, Massachusetts, United States of
America, now of Queen Victoria Street, in the City of London. "IMPROVE
MENTS IN TELEPHONIC INSTRUMENTS."
My Invention relates to telephonic transmitters and is designed to afford the
means for producing a more advantageous effect of the vibratory action of the
sound waves in these instruments than has heretofore been practicable. It is well
known that in speaking into a telephone transmitter the voice produces air-waves
whose phases or alternations of pressure cause the vibrations by whose transmission
through the circuit the sounds are reproduced in the receiver.
· Hitherto telephone transmitters have had their electrodes or those parts by
whose action the vibrations of the sound-waves are communicated to the electric
current so arranged that the sound-waves or vibrations cause variations in the
closeness of contact of such electrodes (or parts) corresponding in order with the
different phases of the sound or air waves, that is to say, the condensations of
the air-waves cause the approximation or increase the compression and the
rarefactions tend to separate or diminish the compression of the said electrodes
or parts.
My present invention relates to the arrangement of the parts of these instru-
ments in such a relative position that the above conditions are reversed, that is to
say, the sound or air waves will so act in my improved instruments as to diminish
the compression or closeness of contact or approximation of the electrodes (or those
portions of the instrument by whose action the vibrations of the air waves are
transmitted to the current) at that phase at which in other instruments there is the
greatest compactness, compression or approximation and vice versa.
If two suitable electrodes are so adjusted that one or both shall be capable of
being freely moved by sound waves or vibrations, and such sound vibrations are
so directed as to act between the electrodes, the condensations of the air will tend
to separate them, and the counteracting force (which may be either their own
elasticity or weight or may be produced by a spring or otherwise) will cause their
approximation or return to their normal position or pressure, and the rarefactions
of the air will assist this counteracting force, as during these rarefactions the air
pressure between the electrodes will be less than that external to them.
This principle of my said invention may be embodied in various forms or modifi-
cations, some of which I have shown in the accompanying drawing. For example,
I may employ an apparatus constructed as shown in Figure 1, which is a longi-
tudinal section, and Figure 2, which is a section of the same on the line x, x,
Figure 1; a is a short tube containing two tongues or blades or the electrodes b, c,
formed of thin metal of a width nearly equal to the diameter of the said tube and
extending longitudinally from the wire terminals b', c', toward the other end of
the said tube.
Each of these electrodes b, is capable of slight movement towards and away
from the other, and both are in connection with wires or conductors b', c¹, from
any source of electricity. When sound waves or vibrations enter the tube a at the
mouth-piece or aperture a¹, they exert their action upon the inner surfaces of the
tongues or electrodes b, c, and it is obvious that the alternate augmentations and
diminutions of density constituting the phases of these air-waves will tend to
cause separations and approximations of the electrodes in the same order of
succession, as above described,

page_text: Another form or modification of my said invention is shown in longitudinal
section in Figure 3, in which one electrode b only is capable of movement the
other c being fixed on a suitable base a.
The above described parts should be so enclosed in a box or case (not shown in
the drawing) as to prevent the action of the air waves or vibrations that enter the
instrument otherwise than between or upon the inner faces of the electrodes b, c.
Another example or modification of the said instrument is shown in Figure 4,
which is a plan, and Figure 5, which is a central transverse section. In this
example I employ a short cylinder or ring a to the opposite flat sides of which I
attach two diaphragms, membranes, or plates b, c, ; these diaphragms or plates may
be of metal and the electrodes are fastened to them in such a manner that their
extremities b², c² meet in the centre of the cylinder a. I form in the said cylinder
two diametrically opposite holes or apertures a¹, a². Any sound vibrations entering
one of these apertures will act upon the plates b, c, in the manner above specified,
that is to say, will cause them to vibrate in phases exactly the reverse of those in
which either would vibrate if acted upon externally and perpendicularly to them.
The above described illustrations or examples of my invention will clearly
explain the principle of action on which the part of our invention to which they
relate is based, and it will be obvious that I may vary or modify the construction
of the said instruments to any extent which will not involve a departure from this
principle, that is to say, in all the forms or modifications of such instruments the
parts must be so arranged that the current will be varied with the vibrations of
the voice or other source of sound, but the effect of the phases of the sounds
relatively to other telephonic transmitters will be completely reversed.
According to another part of my invention shown in longitudinal section in
Figure 6, I construct the transmitter as follows; that is to say, I use a tube a
formed of thin metal or other suitable material and provided at one end with a
convenient mouth-piece or aperture for the reception of the vocal or other sounds.
Near the other end of the tube (but not so near as to prevent or impair its free
vibration by the action of the sound) I surround the said tube with a carbon ring b.
The said ring which should fit closely but not tightly on the tube may be formed
of solid hard carbon or of granulated or powdered coke or the like. In the latter
case I prefer to provide the end of the tube with a cup-shaped piece d formed of
wood, ebonite, or other suitable insulating material, and to form in the same a
circular groove or channel for containing the carbon b. The space at the sides
of the carbon ring within the cup should be packed with felt or the like as
shown at e to prevent the displacement of the carbon b.. One wire of the circuit is
in electrical contact with the outer surface of the carbon ring and the other wire
is in contact with its inner surface through the medium of the tube a if this tube is
formed of metal. When vocal or other sounds enter the mouth-piece or aperture
of the tube a, the air waves or vibrations produced thereby and transmitted
through the tube to the carbon ring b will cause the required variations of
resistance to impart to the current the undulating character necessary for telephonic
purposes.
Having thus fully described my said invention and shown how the same may be
conveniently and advantageously carried into practice I wish it understood that I
do not limit myself to or claim any particular form or construction of telephonic
instruments, irrespective of or not essential in the applications to such instruments
of the novel features above set forth but I claim,-
First. A telephonic transmitter wherein the electrodes (or parts which form the
medium for developing in or transmitting to the current the vibrations of the voice
or other sound) are so arranged that in the phases or variations of density of
the air or sound waves the condensations tend to separate or diminish the com-
pression and the rarefactions tend to approximate or increase the compression of
the said electrodes or parts.
Second. The instrument constructed with two electrodes arranged relatively to
each other and to the mouth-piece or aperture through which the sounds enter and

page_text: enclosed within a tube or case substantially as shown in Figures 1 and 2 of the
drawings, for the purpose specified.
Third. The modification of the said instrument wherein I employ one vibrating
and one fixed electrode substantially as described with reference to Figure 3 of the
drawings, for the purpose specified.
Fourth. The instrument shown in Figure 5 constructed in the form of a cylinder
or ring provided on its flat sides with plates diaphragms or membranes between
and upon which the sound waves or vibrations act and to which are attached
electrodes arranged between the said plates or diaphragms as, and for the purpose,
specified.
Fifth. The instrument wherein the speaking tube is provided with a ring of
carbon or other suitable material arranged in combination with the said tube and
other parts of the said instrument substantially as described with reference to
Figure 6 and for the purpose specified.
In witness whereof I the said Amos Emerson Dolbear have hereunto set my
hand and seal this Fourth day of September in the year of our Lord
One thousand eight hundred and eighty two.
AMOS EMERSON DOLBEAR. (L.S.)