Improvements in Microphones.
Year: 1892

page_text: Date of Application, 11th Nov., 1892
Complete Specification Left, 11th Aug., 1893-Accepted, 16th Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in Microphones.
We, JOHN THOMAS GENT, of Narborough Road, and ALWYN WALTER
STAVELEY and ISAAC HARDY PARSONS, both of 86, Hinckley Road, all in
Leicester, in the County of Leicester, Electricians, do hereby declare the nature of
this invention to be as follows:-
:-
Our invention relates to improvements in granular carbon microphones for
telephonic purposes.
It is well known that the ordinary granular carbon microphone after long use
becomes clogged the particles of carbon gradually shaking closer to each other
until little or no vibration can take place in the diaphragm whereby the speech is
transmitted imperfectly if at all.
According to our invention we provide for rotating the microphone from time to
time, and we advantageously accomplish this as follows.
To the case containing the granular carbon and the diaphragm we attach a
toothed wheel or we form projections upon it and in connection with the lever from
which the receiver is suspended, when the telephone is not in use or to the spring
or bar of the ringing key we arrange or adapt a pawl or projections adapted to
engage with the teeth of the wheel or the projections upon the case in such a
manner that the movement of the lever when hanging the receiver upon the usual
hook or the pressing of the ringing key, causes the said case to be rotated. When
the receiver is lifted off the hook or the ringing key is being pressed returns to
its former position the pawl or projection drops into the next tooth ready for
operation when the receiver is again hung upon the hook. Thus every time the
receiver is taken off and replaced the microphone is moved a distance of one tooth
so that the carbon particles are constantly being moved and prevented from
clogging.
Dated this 11th day of November 1892.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements in Microphones.
We, JOHN THOMAS GENT, of Narborough Road, and ALWYN WALTER
STAVELEY, and ISAAC HARDY PARSONS, both of 86, Hinckley Road, all in
Leicester, in the County of Leicester, Electricians, 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:-
Our invention relates to improvements in granular carbon microphones for
telephonic purposes.
It is well known that the ordinary granular carbon microphone after long use
becomes clogged, the particles of carbon gradually shaking closer to each other
until little or no vibration can take place in the diaphragm whereby the speech is
transmitted imperfectly if at all.
According to our invention we provide for rotating the microphone from time
to time, and we advantageously accomplish this as follows:-
To the case containing the granular carbon and the diaphragm we attach a
toothed wheel or we form projections upon it and in connection with the lever from
which the receiver is suspended, when the telephone is not in use or to the spring or

page_text: bar of the ringing key we arrange or adapt a pawl or projections adapted to engage
with the teeth of the wheel or the projections upon the case in such a manner that
the movement of the lever when hanging the receiver upon the usual hook or the
pressing of the ringing key, causes the said case to be rotated.
When the
receiver is lifted off the hook or the ringing key after being pressed returns to
its former position the pawl or projection drops into the next tooth ready for
operation when the receiver is again hung upon the hook. Thus every time the
receiver is taken off and replaced the microphone is moved a distance of one
tooth so that the carbon particles are constantly being moved and prevented from
clogging.
To enable our invention to be fully understood we will describe the same by
reference to the accompanying drawings, in which :-
Figure 1 is an elevation of a telephone transmitter provided with a microphone
adapted to be rotated, the front of the casing of the apparatus being removed:
Figure 2 is a side elevation partly in section of the apparatus; and
Figure 3 is a side elevation of the casing containing the microphone detached.
a is the backboard of the transmitter and b is the case containing the microphone c
and the diaphragm d, the said case having a journal e, as shewn in Figure 3,
which works in a bearing between the two parts f,f of a divided bracket.
Through the centre of the journal e but insulated therefrom passes a pin which
at its outer end is pointed and in contact with spring connected by a wire h¹
with the primary coil of an induction coil i, the said primary coil being also
connected by a wire with a contact spring against which the pivotted lever k
(upon which the receiver is suspended when the telephone is out of use) is adapted
to come into contact when the said lever is in the position indicated by the dotted
lines in Figure 1, owing to the receiver being removed therefrom. The said pin g is
also in electrical connection with the diaphragm d through the microphone, the
said diaphragm being also placed in electrical connection with the case b.
Upon the case is fixed a ring of ratchet-teeth with which a spring-pawl m
carried upon the lever k is adapted to engage in such a manner that when, after
the telephone has been used, the receiver is hung upon the said lever, the movement
of the latter from the position shewn in dotted lines to the position shewn in full
lines will cause a slight rotation of the microphone. When in using the telephone
the receiver is removed from the lever k, the pawl slips over the ratchet-teeth
of the ring without imparting any movement to the case b.
The circuit of the primary coil is completed through the lever k, the pawl m,
the ratchet ring 7 and the case b.
The secondary coil of the induction coil is arranged in the line circuit in a
well known manner so that it will receive an induced current from the primary coil
of the induction coil. For instance, the secondary current flows from the line
through the binding screw n, the spring contact n' of the call bell, the wire n² and
the wire n³ to the receiver and from the receiver through the wire n' and the wire n³
to the secondary of the induction coil; from the secondary the current flows through
the wire n to the contact spring n' and thence through the lever k and the
bracket to which the said lever is pivotted to the wire n³ and the binding
screw n³ connected to earth or to the return wire of a metallic circuit. The current
flowing through the primary of the induction coil flows through the wire h', the
contact spring h, the pin g, the microphone, the diaphragm d, the case b, the
ratchet-wheel, the pawl m, the lever k, the spring j₁ and the wire j back to
the primary.
o, o¹ are the binding-screws or terminals for the local or bell circuit which may
be arranged in any well known manner.
Although I have described the microphone as being rotated through the medium
of the contact lever from which the receiver is suspended it is to be understood
that any other suitable means may be employed for effecting such rotation, for instance
the push of the call bell might be connected with the microphone in such a manner
that the operation of the push would cause the rotation.

page_text: 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. In a microphone transmitter in which the carbon is in a granular condition
arranging the microphone so that it will be rotated from time to time, substantially
as described.
2. In a microphone transmitter of the kind hereinbefore described, the arrangement
of the microphone and the diaphragm in a case adapted to be rotated by means of
a lever carrying a pawl engaging with ratchet-teeth upon the said case, substantially
as described.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.