Improvements in Microphones.
Year: 1892

page_text: Date of Application, 18th July, 1892
Complete Specification Left, 14th Apr., 893-Accepted, 20th May, 1893
Improvements in Microphones.
I, Sir CHARLES STEWART FORBES, Baronet, 28, Queen's Gate Terrace,
London, S. W. East India Agent, do hereby declare the nature of this invention to
be as follows:
My invention consists in an improved construction of microphone, and in means
for controlling the same.
It is carried out as follows:--Upon a flexible metallic or wooden tympan
preferably packed with soft rubber or equivalent elastic substance, I adjustably
mount a piece of carbon of any suitable shape, the edges of which may be plain or
serrated or grooved; suspended by means of a hinged joint is a thin strip of very.
soft iron which carries at its extremity an adjustably mounted carbon block or
button which may have either a perfectly flat and highly polished surface, or be of
a ring form and serrated if needed. Against the face or upon the inner surface of
the ring the plain or serrated piece of carbon attached to the tympan presses.
A small electro-magnet wound to a high resistance is adjustably mounted near to
the hinged strip and the insulated wire surrounding it connected in shunt to the
terminals of the primary battery circuit. In some cases I mount adjustably or
otherwise a serrated piece of carbon upon the tympan which is caused to lightly press
upon the cylindrical or other surfaces of two pencils of carbon flexibly and
adjustably mounted or suspended near to it, the carbon upon the tympan is fitted
with a soft iron tip and by any suitable means an electro-magnet connected in
shunt as just described is adjustably mounted so as to exert a slight pull upon the
piece of carbon tipped with iron. In either case the electro-magnet is so mounted
and connected as to have the effect of controlling the microphonic contact set up by
the sound waves which results in very clear speech.
An induction or other coil having the same effect may be fitted to or made to
conform to the case containing my improvements.
Dated July 18th 1809
FRANCIS M. ROGERS,
A cant
COMPLETE SPECIFICATION.
Improvements in Microphones.
I Sir CHARLES STEWART FORBES Baronet, 28 Queen's Gate Terrace London,
S.W. East India Agent, 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 :-
My invention consists in an improved construction of microphones and in means
for controlling the same.
It is carried out as follows:-
-
Upon a flexible metallic or wooden tympan preferably packed with soft
rubber or equivalent elastic substance, I adjustably mount a piece of carbon of
any suitable shape, the edges of which may be plain or serrated or grooved;
suspended by means of a hinged joint is a thin strip of very soft iron which
carries at its extremity an adjustably mounted carbon block or button which may
have either a perfectly flat and highly polished surface, or be of a ring form and.
serrated if needed.
Against the face or upon the inner surface of the ring the plain or serrated piece..
of carbon attached to the tympan presses. A small electro-magnet wound to a

page_text: high resistance is adjustably mounted near to the hinged strip and the insulated
wire surrounding it, connected in shunt to the terminals of the primary battery
circuit.
In some cases I mount adjustably or otherwise a scrrated piece of carbon upon
the tympan which is caused to lightly press upon the cylindrical or other surfaces
of two pencils of carbon flexibly and adjustably mounted or suspended near to it,
the carbon upon the tympan is fitted with a soft iron tip and by any suitable means
an electro-magnet connected in shunt as just described is adjustably mounted so as
to exert a slight pull upon the piece of carbon tipped with iron.
In either case the electro-magnet is so mounted and connected as to have the
effect of controlling the microphonic contact set up by the sound waves which
results in very clear speech.
An induction or other coil having the same effect may be fitted to or made to
conform to the case containing my improvements.
To enable my invention to be better understood, I will now more particularly
describe the same by means of the accompanying drawings in which:
Fig. 1 is a vertical section upon line A. B Fig. 2.
Fig. 2 is a back view of a complete instrument part of the case being removed.
Figs. 3 & 4 are vertical sections of modifications.
Fig. 5 is a detail view of taper carbon contact.
In the drawings 1, is the tympan which I prefer to form of ordinary ferrotype
iron plate, this however, may be replaced by a thin piece of pine wood, but in either
case the tympan is packed on both sides with soft rubber rings 2, and clamped by
means of metal threaded screws 3, between two brass rings 4, which are fastened to
the wood of case 5, by means of ordinary wood screws 3. A hole 23, is turned out
of the front of the case 5, and the sound waves are collected by a wooden or other
mouth-piece 24, secured thereto by glueing or other suitable means.
acts
In cutting out the innermost rubber ring 2, I prefer to leave a tongue 6, which
as a damper upon the ferrotype plate and prevents undue sensitiveness.
Mounted upon a soft rubber pad 61 and secured by screws 31 passing through it
into the top of the case is an insulated metallic rectangular bracket 7, to the
shorter leg 7 of this bracket is hinged a light strip of carefully annealed wrought
iron 8, the lower end of this strip terminates in a metal dise a, preferably of brass,
which is secured to the strip by means of the screw b. A button of carbon 9, is
coated by means of electro deposition with copper upon its under side, and is then
sweated to the disc with solder.
The front face of the carbon block 9 is highly polished, and is always more or
less in contact with the carbon contact piece 91, which is similarly coppered and
united to any suitable part of the tympan 1. Behind the carbon block 9, is an
adjustment composed of a screw 10, which engages with a plate 11, secured by
screws 31 to the back of the case. It will be readily understood that by turning
the screw 10 to the right or left hand the position of the strip 8, and the button 9,
may be regulated with regard to the electro-magnet 12. This magnet consists of
a bobbin 12 of metal, filled with insulated wire d, of relatively high resistance to
the primary circuit from which it is derived, the ends of the wires d, are connected
to the hinges 15, 15' which also serve to flexibly connect the battery circuit by
means of wires p, with the microphone contacts 9, 9, and the primary wire of
induction coil 13.
The core 12 of the electro magnet 12, is screwed at its inner end and by turning
it slightly with a screw driver inserted in the nick 12 the slotted seat e, soldered
to or forming part of the bobbin 12 may be clamped in any desired position upon
the longer leg 7" of the bracket 7, which passes through it.
In any convenient part of case 5 is mounted by glueing or screws an ordinary
induction coil 13, having a core of annealed iron wires 14. The primary wire p
proceeds from terminal P and is wound round the core 14, and connected to the
edge of the tympan plate 1, by soldering, the other end of the primary wire is
connected to hinge 15, and from thence to the insulated bracket 7, and terminal P

page_text: a third wire p is connected to hinge 15'. The local battery L, is coupled up to
terminals P. P. The high resistance wires d, of the electro-magnet 12, are soldered
to the two hinges 15, 151, thus forming a shunt to the primary circuit. The object
of connecting the shunt and primary wires to the hinges is to enable the front part
of the case containing all the working parts, except the induction coil and adjust-
ment, to be opened om. The operation of my invention is as follows :-
-
When the sound waves fall upon the tympan 1, a variable current passes
between the loose contacts 9, 91, and since the current flowing in the shunted electro-
magnet circuit varies in a ratio depending upon that passing in the primary, the
core of the electro-magnet attracts the soft iron strip 8, carrying the button 9, the
effect being to exert upon the contacts 9, 9', exactly the pressure required to give
clear, articulate sounds in the telephone T, connected to the line circuit L' passing
through the terminals SS, and secondary wire s, s, surrounding coil 13, to earth
plate E, thereby avoiding the hissing or singing due to uncertain or rebounding
contact. It follows therefore, that, irrespective of the action above mentioned, the
shunted electro-magnet will exert a greater or less pressure upon the loose
contacts 9, 9, directly in proportion to the strength of battery employed and the
contact pressure caused by the impress of the sound waves, thus rendering the
instrument self adjusting.
A modification of my invention is shewn in Fig. 3. It consists in attaching to a
metallic tympan, a plain or serrated conical carbon cone 9', which is capped with
a small iron armature 9" fastened to it by a screwed pin, passing through the
tympan 1.
The contact 9, consists of a plain or serrated ring mounted upon a ring of
brass 16, by sweating with solder as previously described, the ring 16 being fastened
by screws 3' to the thin wooden plate 17. Or if desired the carbon ring 9 may be
cemented with glue direct to the plate 17. Behind the plate is the bobbin 12' of
the shunted electro-magnet 12, the core of this electro-magnet 12", is square shaped
at its outer end 12°, threaded, and passes through a milled nut 19, and a square
hole 19 formed in the forked bracket 20, fastened to the plate 17, by screws 3'.
One of the primary wires p, is soldered to the metallic tympan 1, the other to the
brass plate 16, the shunt wires d, d, are secured as before to the hinges. By
turning the milled nut 19, the core 12 of the electro-magnet 12, is regulated so as
to exert the required pull upon the armature 9" attached to the plain or serrated
cone 91, secured to the tympan 1.
Fig. 4, shews the application of my invention to transmitters having vertical
cylindrical carbons. In this case attach by cementing with glue or the like,
preferably to a wooden plate 17, packed with soft rubber strips 2, secured by means
of screws 3, passing through the metallic bridge 20, into the case 5, the cylindrical
carbon contacts 9, the contacts are pointed or journalled and are free to move in
the holes drilled in the blocks 9" fastened by small wood screws 31 to the plate 17.
Upon the metallic tympan 1, packed with rings 2, is mounted by electro-typing
and sweating with solder the serrated tapering carbon contact 91 fitted with an
armature 9 secured to it by a pin (see also Fig. 5). The outer end of the
magnet core 12 is square, threaded as at 12, and passes through a square hole 191
in the bridge 20.
Two nuts 19, serve the purpose of adjusting the core to the required distance
from armature 9¹¹.
When the loose contacts are mounted upon wooden tympans, the circuit connec-
tions are made direct to them as shewn in Fig. 3.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. In an electric telephone transmitter the combination of an adjustable electro
magnet forming a shunt to the primary circuit for controlling the loose carbon
contacts in the way and manner described.

page_text: 2. In an electric telephone transmitter, the combination of a loose carbon
contact 9, secured to a soft iron strip 8, hinged to the insulated bracket 7, screwed
to case 5, the pressure between the loose carbon contacts 9, 91, included in the
primary circuit being regulated by the shunted adjustable electro-magnet 12, in
the way and manner described.
3. In an electric telephone transmitter controlled by a shunted electro-magnet,
the screw 10, threaded in plate 11, secured to case 5, for adjusting the position of
the carbon electrodes 9, 9', by regulating the position of strip 8, in the field of the
electro-magnet 12, as described.
4. In an electric telephone transmitter the electrodes of which are controlled by
a shunted electro-magnet in the manner described, the combination and employ-
ment of the induction coil 13, the primary and secondary circuit connections
thereto and therefrom.
5. In an electric telephone transmitter, the combination of a plain or serrated
carbon cone 9 having an armature 9" and engaging with a plain or serrated carbon
ring 9, both being within the primary circuit, their relative position being controlled
by the action of the shunted electro-magnet 12, upon the armature 9", substantially
as shewn and described in Fig. 3.
6. In an electric telephone transmitter, the combination of a tapered, plain or
serrated carbon electrode 91, having an armature 911 with the loose carbon
cylinders 9, mounted as described, regulation being effected by the action of the
shunted electro-magnet 12, upon the armature 911 substantially as described and
shewn in Fig. 4.