Improvements in Microphones for Telephonic Circuits, and in the Induction Coils thereof.
Year: 1891

page_text: Date of Application, 11th Apr., 1891
Complete Specification Left, 23rd Dec., 1891-Accepted, 23rd Jan., 1892
PROVISIONAL SPECIFICATION.
Improvements in Microphones for Telephonic Circuits, and in the
Induction Coils thereof.
We, EUGENE GWOSDEFF, Gentleman and ANDREAS BUNGE, Civil Engineer
both of Boulevard Konnogwardeisky No. 20 St. Petersburg Russia, do hereby
declare the nature of this invention to be as follows:-
In microphones for telephonic circuits the diaphragm is intended to receive the
sonorous undulations of the air, to enter into vibration and to transmit the vibratory
movement to microphonic carbon contacts. Practical experience has shewn that
the best material for such diaphragms is dry pine wood with close grained fibre,
but as yet no definite data have been obtained as to the most favorable dimensions
or form thereof. It was only known that for the transmission of loud speech and
to great distances, microphones should have a diaphragm of as large a size as
practicable.
In increasing the surface of the diaphragm, it will soon be observed that the
transmission becomes more or less indistinct and distorted, and this will occur
sooner when transmitting speech than with the transmission of musical sounds.
Microphones of the Ader type provided with comparatively large diaphragms,
the force of transmission of which is very considerable, have been found more
suited for transmitting musical sounds than for speech, while the modifications of
the Ader microphone can only transmit speech with smaller diaphragms and with
systems of dampers or moderators, which cause the transmission to be considerably
weakened.
Our invention relates to means whereby the detrimental influence of large
diaphragms upon the transmission is obviated, and which we will proceed to describe
with reference to the accompanying drawings.
Figure 1 of the drawings shews a pine wood diaphragm of rectangular form.
The fibres of the wood are arranged parallel to the sides A B and C D.
Two plates a and b of the same wood are glued to the diaphragm, the fibres of
these plates being placed transversely to those of the diaphragın. The carbons of
the microphone are fixed to the plates a and b and not to the diaphragm itself.
Figure 2 shews a diaphragm of circular form, the fibres being in this case parallel
to the diameter A B, and the fibres of the plate a glued thereto, on which is the
microphone contact, are at right angles to those of the diaphragm.
With this arrangement all the fibres of the diaphragm transmit their motion to
the microphone contact, and the surface of the diaphragm could be increased at
will without any derangement in the sound transmission resulting therefrom.
This is explained by the fact that human speech is composed of a long series of
musical sounds of different pitch. These sounds cause the fibres of the diaphragm
to vibrate differently. Each fibre can only vibrate to the fullest extent under the
influence of a certain sound.
Notwithstanding the equal length of the fibres of a rectangular diaphragm, they
do not all behave in the same manner relatively to musical sounds, and their
vibrations are not identical.
The transverse plates a bare influenced by the collective vibrations of all the
fibres of the diaphragm, and transmit their composite vibratory motion to the
microphone contact.
The same circumstance as above stated takes place with a circular diaphragm,
but to a greater extent, because in this case the fibres are of different length: but
he plate a transmits the movements of all the vibrating fibres.

page_text: In the microphones heretofore constructed, it has not been possible to subject
the carbons to the action of all the fibres of the diaphragm, as the latter always
acts upon the microphone contact by part only of these fibres.
The greater the number of fibres acting directly upon the carbons of the
microphone, the louder will be the transmission of sound, as with the Ader
microphone, while as to the fibres that are not connected to the microphone,
they will vibrate under the influence of the sound undulations and these
vibrations will derange the character of the vibratory movements of the fibres
acting upon the carbon.
The derangement of the transmission increases with the number of the free or
unconnected fibres. If the microphonic contact is placed at the centre of the
diaphragm the derangement is increased to a maximum, and there is no micro-
phone with the contact at the centre that is not provided with a system of
brakes or dampers of varying construction, the object of which is to prevent
the vibration of the free fibres. The strength of transmission depends however
directly upon the extent of the diaphragm submitted to the action of the sound
waves.
Another essential element in the proper working of microphones is the
induction coil. It is known that in the secondary coil of a Kuhmkorff coil,
two induced currents are produced, which are quite different from cach other,
both as regards tension and duration. Thus the current produced in the
secondary coil at the moment of closing the primary circuit, or of increasing
the inducing current therein, is slower and of lower tension than the induced
current which is formed at the moment of rupture of the primary circuit or, of
the decrease of the inducing current. It follows that the induction coil placed
opposite the microphone sends into the line wire alternating currents of unequal
force in both directions, and the currents produced by the rupture or decrease
of the inducing current will always predominate.
All decrease or increase of the microphone current in the primary coil is the
result of a change in the resistance of the microphone contacts.
This change in the resistance of the contacts is produced in its turn by the
vibrations of the diaphragm under the action of the sound waves.
The diaphragms constructed according to our invention with consolidated fibres
transform the action of the sound waves into alternating variations of the resistance
of the primary circuit of the microphone coil which variations are as nearly as
possible similar to the vibrations of the air.
In the ordinary induction coils the transformation of the currents being
irregular, the curve representing the alternate currents of the secondary coil
can never be similar to the curve of the intensity of the current in the primary
coil, and this is the primary cause of the defective transmission of the micro-
phones, which are sometimes unable to transmit certain sounds at all, such as
sibillant or hissing consonants. It is evident that speech becomes all the more
indistinct, the greater are the number of consonants omitted. On long lines this
omission of certain consonants is increased still further through the special
properties of the conductor as regards self-induction and electrical capacity.
It will be understood that in this case the irregularities of the transformation
of the currents by the coils exercise a still greater influence upon the limits of
the distance to which the transmission of speech can be effected with distinctness.
The method which we will proceed to describe, if it does not effect the
complete annulment of the detrimental influence of the transformation of the
currents upon the clearness of transmission of speech, at any rate renders nearly
identical the curves representing the intensity of the currents sent into the line,
and the variations of the inducing current in the primary coil.
Fig. 3 of the drawing shews two Ruhmkorff coils of equal electrical elements,
that is to say, in which the resistance, the number of windings of the primary and
secondary coils, the iron cores, the diameter, and the length and coefficient of self-
induction are identical; they are also both coiled in the same direction.

page_text: The entering ends of the primary coils p' p' are connected to each other and to
the battery.
The outgoing end of induction coil No. 1 is connected to the "Neff "interrupter a,
making contact with the spring connected to the other pole of the battery B.
By this arrangement, the current circulates in the primary coil of No. 1 and
magnetises the core.
The interrupter a, being attracted, is separated from the spring b, the motion of
which is limited by the conducting stop which supports it while the interrupter
descends to the core. The contact between a and ceasing, the current no longer
passes through the primary coil of No. I and passes into the primary coil p" of
No. II, the wire of which is connected to the stop e.
In the secondary coils S S and S, S₁ of the two transformer coils, currents will
be induced simultaneously, but in the one the current will be due to the interruption
and in the other it will be due to the closing of the inducing circuit. The ends of
the secondary coils of the two induction coils can be connected together in tension
or in quantity, according to requirements, but in such manner that in the two
cases the current produced by the interruption of the inducing circuit is added to
the current produced by the closing.
By this arrangement there are obtained two currents of opposite direction but
almost identical as to intensity and duration.
These currents thus equalised are conveyed into the linewire.
In replacing the "Neff" interrupter by a microphone with contacts suitably
arranged so that the increase and decrease of the resistance in the primary circuits
of the two coils take place simultaneously, there are obtained under the influence of
the sound waves alternating currents equalized in the same manner.
For the sake of clearness we have shewn at Fig. 4 the application of a Hughes
microphone.
a a is the vibrating diaphragm the fibres of which are consolidated by a transverse
piece glued thereto. The transverse piece carries a carbon having two
cavities in which bear the points of two carbons e₁ the other ends of which are
situated in the cavities of two fixed carbons d d, so that the carbon de is inclined
to the left and the carbon d₁ e₁ to the right. When the diaphragm is displaced to
the right, the resistance at ₁₁ d increases while that in ce d₁ decreases, and
The current of the battery enters at c'and divides into c, e d and e e, d₁.
It then passes through the two branches to the entering ends p p of the primary
coils of the induction coils 1 and 2; the outgoing ends and p of these primary
coils are connected to the battery.
vice versa.
Fig. 5 shews a cross section and sectional plan of the invention as applied to a
microphone with carbons in rod forin, which displace themselves freely on inclined
planes.
The diaphragm a a is provided with two frames of wood glued to the diaphragm
in such manner that one of the sides of each frame connects all the fibres of the
diaphragm with each other.
Within the frames are fixed four carbons d d and d₁ dr.
Between the two frames and parallel to the diaphragm is securely fixed a plate e
provided with inclined pins serving as guides for the carbons, the inclination of the
pins being the same in each case. The carbons ce and c c which can roll freely
upon the pins, displace themselves in different directions and bear against the
carbons d d. In consequence of the vibrations of the diaphragmn, the resistance at
the points of contact of the carbons at the left hand increases when it decreases at
the right hand carbons, and vice versa. The induction coils are connected to the
microphone in the same way as in the preceding case, that is to say, the current
from the battery enters the two left hand carbons d and d₁ divides, and passes
through the carbons ccc..
and 1 C₁ C1 to the right hand carbons d d₁
on passing from these, one branch of the current is connected to the entering end pl
of the primary coil of induction coil No. 1, and the other to the entering end p₁ of

page_text: the primary coil of induction coil No. 2; the other ends p and p¹¹ return to the
battery.
Dated this 11th day of & nil 1901
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE
SPECIFICATION.
Improvements in Microphones for Telephonic Circuits, and in the
Induction Coils thereof.
We, EUGENE GWOSDEFF, Gentleman, and ANDREAS BUNGE, Civil Engineer,
beth of Boulevard Konnogwardeisky No. 20, St. Petersburg, Russia, 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—
In microphones for telephonic circuits the diaphragm is intended to receive the
sonorous undulations of the air, to enter into vibration and to transmit the vibratory
movement to microphonic carbon contacts. Practical experience has shown that
the best material for such diaphragms is dry pine wood with close grained fibre,
but as yet no definite data have been attained as to the most favourable dimensions
or form thereof. It was only known that for the transmission of loud speech and
to great distances, microphones should have a diaphragm of as large a size as
practicable.
In increasing the surface of the diaphragm it will soon be observed that the
transmission becomes more or less indistinct and distorted, and this will occur
sooner when transmitting speech than with the transmission of musical sounds.
Microphones of the Ader type provided with comparatively large diaphragms,
the force of transmission of which is very considerable, have been found more
suited for transmitting musical sounds than for speech, while the modifications of
the Ader microphone can only transmit speech with smaller diaphragms and with
systems of dampers or moderators, which cause the transmission to be considerably
weakened.
Our invention relates to means whereby the detrimental influence of large
diaphragms upon the transmission is obviated, and which we will proceed to describe
with reference to the drawings accompanying our Provisional Specification.
Figure 1 of the drawings shews a pine wood diaphragm of rectangular form.
The fibres of the wood are arranged parallel to the sides A B and C D.
Two plates a and 6 of the same wood are glued to the diaphragm, the fibres of
these plates being placed transversely to those of the diaphragm. The carbons
of the microphone are fixed to the plates a and band not to the diaphragm
itself.
Figure 2 shews a diaphragm of circular form, the fibres being in this case
parallel to the diameter A B, and the fibres of the plate a glued thereto,
on which is the microphone contact, are at right angles to those of the
diaphragm.
With this arrangement all the fibres of the diaphragm transmit their motion
to the microphone contact, and the surface of the diaphragm could be increased
at will without any derangement in the sound transmission resulting therefrom.
This is explained by the fact that human speech is composed of a long series
of musical sounds of different pitch. These sounds cause the fibres of the diaphragm
to vibrate differently. Each fibre can only vibrate to the fullest extent under the
influence of a certain sound.
Notwithstanding the equal length of the fibres of a rectangular diaphragm, they
do not all behave in the same manner relatively to musical sounds, and their
vibrations are not identical.

page_text: The transverse plates a bare influenced by the collective vibrations of all the
fibres of the diaphragm and transmit their composite vibratory motion to the
microphone contact.
The same circumstance as above stated takes place with a circular diaphragm
but to a greater extent, because in this case the fibres are of different length; but
the plate a transmits the movements of all the vibrating fibres.
In the microphones heretofore constructed, it has not been possible to subject
the carbons to the action of all the fibres of the diaphragm, as the latter always acts
upon the microphone contact by part only of these fibres.
The greater the number of fibres acting directly upon the carbons of the
microphone, the louder will be the transmission of sound, as with the Ader
microphone, while as to the fibres that are not connected to the microphone,
they will vibrate under the influence of the sound undulations and these vibrations
will derange the character of the vibratory movements of the fibres acting upon the
carbon.
The derangement of the transmission increases with the number of the free or
unconnected fibres. If the microphonic contact is placed at the centre of the
diaphragm the derangement is increased to a maximum, and there is no microphone
with the contact at the centre that is not provided with a system of brakes or
dampers of varying construction the object of which is to prevent the vibration of
the free fibres. The strength of transmission depends however directly upon
the extent of the diaphragm submitted to the action of the sound waves.
Another essential element in the proper working of microphones is the induction
coil. It is known that in the secondary coil of a Ruhmkorff coil, two induced
currents are produced, which are quite different from each other, both as regards
tension and duration. Thus the current produced in the secondary coil at the
moment of closing the primary circuit, or of increasing the inducing current
therein, is slower and of lower tension than the induced current which is formed
at the moment of rupture of the primary circuit or of the decrease of the inducing
current. It follows that the induction coil placed opposite the microphone sends
into the line wire alternating currents of unequal force in both directions, and the
currents produced by the rupture or decrease of the inducing current will always
predominate.
All decrease or increase of the microphone current in the primary coil is the
result of a change in the resistance of the microphone contacts.
This change in the resistance of the contacts is produced in its turn by the
vibrations of the diaphragm under the action of the sound waves. The diaphragms
constructed according to our invention, with consolidated fibres transform the action
of the sound waves into alternating variations of the resistance of the primary
circuit of the microphone coil which variations are as nearly as possible similar to
the vibrations of the air.
In the ordinary induction coils the transformation of the currents being irregular,
the curve representing the alternate currents of the secondary coil can never be
similar to the curve of the intensity of the current in the primary coil, and this is
the primary cause of the defective transmission of the microphones, which are
sometimes unable to transmit certain sounds at all, such as sibillant or hissing
consonants. It is evident that speech becomes all the more indistinct, the greater
are the number of consonants omitted. On long lines this omission of certain
consonants is increased still further through the special properties of the conductor
as regards self-induction and electrical capacity. It will be understood that in this
case the irregularities of the transformation of the currents by the coils exercise a
still greater influence upon the limits of the distance to which the transmission
of speech can be effected with distinctness.
The method which we will proceed to describe, if it does not effect the complete
annulment of the detrimental influence of the transformation of the currents upon
the clearness of transmission of speech, at any rate, renders nearly identical the

page_text: .
curves representing the intensity of the currents sent into the line, and the variations
of the inducing current in the primary coil.
Fig. 3 of the drawing shews two Ruhmkorff coils of equal electrical elements,
that is to say, in which the resistance, the number of windings of the primary and
secondary coils, the iron cores, the diameter, and the length and coefficient of self.
induction are identical; they are also both coiled in the same direction.
The entering ends of the primary coils p' pare connected to each other and to
the battery. The ontgoing end of induction coil No. 1 is connected to the "Neft"
interrupter a, making contact with the spring b connected to the other pole of the
battery B.
By this arrangement, the current circulates in the primary coil of No. 1 and
magnetises the core.
The interrupter a, being attracted, is separated from the spring the motion of
which is limited by the conducting stop, which supports it while the interrupter
descends to the core. The contact between a and ceasing, the current no longer
passes through the primary coil of No. 1 and passes into the primary coil pof
No. II, the wire of which is connected to the stop c.
In the secondary coils S S and S, S₁ of the two transformer coils, currents will
be induced simultaneously, but in the one, the current will be due to the inter-
ruption and in the other it will be due to the closing of the inducing circuit. The
ends of the secondary coils of the two induction coils can be connected together in
tension or in quantity, according to requirements, but in such manner that in the
two cases the current produced by the interruption of the inducing circuit is added
to the current produced by the closing.
By this arrangement there are obtained two currents of opposite direction but
almost identical as to intensity and duration.
These currents thus equalized are conveyed into the linewire.
In replacing the Neff interrupter by a microphone with contacts suitably arranged
so that the increase and decrease of the resistance in the primary circuits of the two
coils take place simultaneously, there are obtained under the influence of the sound
waves alternating currents equalised in the same manner.
For the sake of clearness we have shewn at Fig. 4 the application of a Hughes
microphone.
a a is the vibrating diaphragm the fibres of which are consolidated by a
transverse piece glued thereto. The transverse piece carries a carbon c,
having two cavities in which bear the points of two carbons e e, the other ends
of which are situated in the cavities of two fixed carbons d d₁ so that the
carbon de is inclined to the left and the carbon d, e, to the right. When the
diaphragm is displaced to the right, the resistance at c, ed increases while that
inced decreases, and vice versa. The current of the battery enters at c and
divides into c₁ed and. ce, d₁. It then passes through the two branches to the
entering ends of the primary coils of the induction coils to 1 and 2; the
outgoing ends p and p₁ of these primary coils are connected to the battery,
Fig. 5 shews a cross section and sectional plan of the invention as applied to
a microphone with carbons in rod form, which displace themselves freely on inclined
planes.
The diaphragm aa is provided with two frames of wood glued to the diaphragm
in such manner that one of the sides of each frame connects all the fibres of the
diaphragm with each other.
Within the frames are fixed four carbons d d and d₁ d₁.
Between the two frames and parallel to the diaphragm is securely fixed a plate e
provided with inclined pins serving as guides for the carbons, the inclination of
the pins being the same in each case. The carbons cc and c₁ c₁ which can roll
freely upon the pins, displace themselves in different directions and bear against
the carbons dd₁. In consequence of the vibrations of the diaphragm, the resistance
at the points of contact of the carbons at the left hand increases when it decreases

page_text: at the right hand carbons, and vice versa. The induction coils are connected to the
microphone in the same way as in the preceding case, that is to say, the current
from the battery enters the two left hand carbons d and d₁ divides, and passes
through the carbons c c c... and ₁₁₁ to the right hand carbons d d₁;
on passing from these, one branch of the current is connected to the entering
end p of the primary coil of induction coil No. I and the other to the entering
end of the primary coil of induction coil No 2; the other ends p and p¹¹ return
to the battery.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what
we claim is :-
1. The use in microphones for telephonic circuits, of diaphragms, the vibrating
fibres of which are connected together by means of transverse plates, the micro-
phonic contact pieces being exclusively attached to the said transverse plates,
substantially as described.
2. In telephonic circuits arranging the induction coils in such manner that the
transformation of the current is effected simultaneously in two precisely similar
coils, the inducing current being made to divide into the two primary coils of the
apparatus, and the closing of the circuit or strengthening of the current in one
of the branches being made to coincide with the interruption of the circuit or
the weakening of the current in the other branch, substantially as and for the
purposes described.
Dated this 23rd day of December 1891.
ABEL & IMRAY,
Agents for the Applicants.