Improvements in Apparatus for the Transmission and Reproduction of Sounds.
Year: 1895

page_text: Date of Application, 17th Dec., 1895
Complete Specification Left, 17th Sept., 1896-Accepted, 17th Oct., 1896
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for the Transmission and Reproduction
of Sounds.
We, THOMAS JAMES HOWELL, of 1 Westmorland Place, City Road, in the
County of London, Engineer, GEORGE POCOCK, of 75 Victoria Road, Clapham
Common, in the County of Surrey Gentleman, and PERCY ROGERS POCOCK, of
210 Anerley Road, Anerley, in the County of Surrey, Gentleman, do hereby
declare the nature of this invention to be as follows:-
This invention relates to apparatus for the transmission and reproduction of
sounds.
In the Specification of a prior Patent No. 18773 granted to one of us viz. Thomas
James Howell on the 30th day of October 1891 an instrument capable of serving
both as a transmitter and as a receiver of sounds was described. It is the chief
object of the present invention to improve instruments of this kind.
According to our invention the instrument comprises a suitably shaped case or
box of insulating or insulated material furnished with an ear-piece or mouth-piece
of any convenient form. Within this case or box one or more pieces of magnetized
steel are provided, the said pieces of steel being similar to those referred to in the
specification abore cited, that is to say they extend across the case of the
instrument and are so bent that their outer ends lie in proximity to a diaphragm
or tympan. These magnetized pieces of steel are according to our present
invention held in place by a flanged tube of soft iron, having holes in its flange to
receive screws or other means for holding both the tube and the pieces of steel
firmly in position. The interior of this flanged tube is screw threaded to receive a
soft iron core which is correspondingly screw threaded to permit of its distance
from the diaphragm or tympan to be adjusted by revolving the said core in one or
other direction. Around the free end of the said flanged tube an ordinary coil or
bobbin of insulated wire is arranged. The said coil or bobbin may be affixed to
an annular partition which extends trausversely across the case or box, a space
being left between the said partition and the base of the case or box so that a
sound box is thereby produced. Upon this partition we secure an annular disc or
ring of carbon or other suitable material, the said disc or ring being formed in two
picces or halves, whose ends are kept a short distance apart by any suitable means.
Upon the divided annular disc or ring we place a quantity of granulated or
powdered carbon or metallic filings or any other suitable granular material that is
an electric conductor. This granulated or powdered material is kept in place by
a piece of paper or an annular plate of mica carbon or metal and the diaphragm
or tympan is preferably arranged in front of the said piece of paper or plate of
mica carbon or other material.
The space between the proximate ends of the halves or portions of the
aforesaid divided annular disc or ring may be filled with wax or other suitable.
non-conducting substance to prevent the granulated material from escaping between
the said ends.
)
One of the halves or portions of the divided annular disc or ring is connected.
to a terminal on the exterior of the instrument and the other half or portion is
connected to one end of the said coil or bobbin of insulated wire surrounding the
Bauged tube. The other end of this coil or bobbin of wire is connected to another
exterior terminal.
!

page_text: It will thus be seen that a microphone transmitter and electro-magnetic receiver
is formed in which the electric circuit is completed from one half or portion of the
divided annular disc or ring through the powdered or granulated carbon to the
other half of the said annular disc or ring.
Instead of using the aforesaid pieces of magnetized steel and the flanged tube
with its adjustable soft iron core arranged as herein before mentioned, we may
employ one or more bars or plates of magnetized steel of any suitable section
placed inside the case or box preferably near the centre, and so arranged that
their axes are approximately perpendicular to the plane of the diaphragm or
tympan.
If we use more than one of the said magnetized steel bars or plates the ends
farthest from the diaphragm are connected together by a plate of brass or by any
suitable non-magnetizable substance. An adjusting screw is provided at the back
of the case and the inner end of this screw engages with the aforesaid brass plate
carrying the magnetized steel bars. The outer end of the said screw is furnished
with a milled head or other appropriate means for revolving it so that the position
of the inner ends of the magnetized bars can be adjusted relatively to the
diaphragm.
When two or more of the magnetized steel bars are employed we prefer to so
arrange them that their ends of similar polarity are in proximity to each other.
Instead of using bars or plates of magnetized steel connected as aforesaid we
may use a magnet or magnets of horseshoe type the connections between the coils
surrounding the poles being made accordingly.
Instead of regulating the distance between the diaphragm or tympan and the
magnet or magnets by adjusting the position of the said magnet or magnets we
may so arrange the diaphragm that it will be capable of movement towards or
away from the said magnet or magnets.
If desired we may make use of both these methods of adjustment in the same
instrument.
Instead of forming the aforesaid divided annular disc or ring in halves as above
stated we may form it of any suitable number of sections.
Dated this 17th day of December 1895.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicants.
Improvements in Apparatus for the Transmission and Reproduction
of Sounds.
We, THOMAS JAMES HOWELL, of 43 Millais Street, Albany Road, Camberwell
Road, in the County of London, late of 1 Westmorland Place, City Road, in the
County of London, Engineer, GEORGE POCOCK, of 75 Victoria Road, Clapham
Common, in the County of Surrey, Gentleman, and PERCY ROGERS POCOCK,
of 210 Anerley Road, Anerley, in the County of Surrey, Gentleman, do hereby
declare the nature of this invention and in what mauner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:—
This invention relates to improvements in telephonic instruments that are capable
of serving both as transmitters and receivers and the said improvements are
particularly applicable to instruments of the kind or class described in the
Specification of prior Letters Patent No. 18773 A.D. 1891. The improvements
are not however intended to be confined to instruments having L-shaped permanent
magnets such as those described in said prior specification.

page_text: The chief feature of our invention has reference to the construction of the
carbon or other plates with which the carbon or other granules of the microphone
transmitter make contact. A further feature of the said invention is the
adjustability of the soft iron core or of the permanent magnet or magnets with
reference to the vibratory diaphragm as hereinafter described the coils surrounding
the core or magnet as the case may be being maintained stationary during such
adjustment of the core or magnet. Our invention also comprises improvements in
the details of construction as hereinafter described.
Referring to the accompanying drawings,
Figure 1 is a central longitudinal section of one form of instrument constructed
in accordance with our invention.
Figure 2 is a front elevation of the instrument with the mouth piece, diaphragm,
and granulated carbon removed.
Figures 3, 4 and 5 are longitudinal sections of the tube containing the core
hereinafter described, and illustrate different methods of securing the tube to the
case and of adjusting the core.
Figures 6 and 7 are views similar to Figures 1 and 2 but show a modified form
of instrument containing two straight permanent magnets.
Figure 8 is an elevation of the front end of the said instrument with the mouth
piece, the diaphragm, and the carbon plates removed, to show the leading-in
wires and their connections.
Figure 9 is a cross section on the line x, x of Figure 6.
Figure 10 is an elevation of the rear end of the instrument.
Figure 11 is a plan of a modified form of magnet suitable for use in our improved
instrument.
Figure 12 is a section of the same on the line y, y, Figure 11, and
Figure 13 is a plan of another shape of magnet for the same purpose.
Like letters of reference denote corresponding parts throughout the drawings.
A is the case of the instrument which is suitably insulated or is made of
insulating material; B is the mouth piece; C is the diaphragm; D, D are the
permanent magnets which are strongly magnetised.
Referring now particularly to Figures 1 and 2 the permanent magnets there shown
are similar to those referred to in the specification above cited, that is to say, they
are L-shaped and are arranged radially and extend across the case of the instrument
from the centre to the peripheral wall. Their upstanding outer ends which are of
similar polarity lie in proximity to the diaphragm or tympan C. They are held in
place by the collar E' forming part of a tube of soft iron E which extends through
back of the case and which is retained in place by a nut E2. The said collar
bear on the inner adjacent ends of the magnets. In Figure 3 screws E* are shown
passing through the collar E' and through the back of the case of the instrument
and screwing into a plate E' outside the case. In Figure 5 the screws are
arranged to screw into the back of the case. Within the tube E is a soft iron
core which may be screw-threaded and adapted to fit the corresponding screw-
threaded internal cavity of the tube E as shown in Figures 1 and 5 so as to permit
of axial adjustment of the core by turning the same, or the core may be plain at
that part which fits the tube and be adjustable by having its screw-threaded end
screwed into the plate E' as shown in Figure 3 or into the nut E' as shewn in
Figure 4. By adjusting the core relatively to the tympan C the attraction of
the magnet upon the tympan is increased or diminished as required. Around the
free end of the tube E an ordinary coil or bobbin G of insulated wire is
arranged. The said coil or bobbin may be affixed to an annular partition H of
any insulated or insulating material which partition extends transversely across
the case or box A, a space being left between the said partition and the back of
the case or box so that a sound-box is thereby produced.
K, K are the two parts of an annulus or ring of carbon or other suitable
material surrounding the coil G the two parts being formed by splitting the said
ring diametrically as indicated in Figure 2. The said parts are secured by

page_text: screws J, J¹ or otherwise to the partition H or, in case there is no partition, to
washers or other suitable supports. The ends of the two parts K K are kept a
short distance apart by any suitable means. The space between them may be
filled with wax, rubber tape, or other suitable electrically insulating substance to
prevent the escape of the granulated material hereinafter referred to between the
said ends, but if they are arranged sufficiently close to each other to prevent such
escape while still being out of contact the insulating material is not necessary.
The circular edge of the ring nearest the coil or bobbin is preferably chamfered.
Upon the flat face of the divided or segmental annulus or ring and between the
ring and the diaphragm we place a quantity of granulated or powdered carbon or
metallic filings or any other suitable granular material L that is an electrical
conductor. This granulated or powdered material is conveniently kept in place by
a piece of paper L₁ or by an annular plate of mica, carbon or metal or other
suitable substance the edge of which is secured to the case or box A. The
diaphragm or tympan is arranged in front of the said piece of paper or plate of
mica or other material, a wire ring c or other distance piece being if desired
provided to prevent contact of the diaphragm with the paper or other cover L'.
The magnets D are insulated by wax, rubber tape or otherwise from the carbon
annulus K, K', and from the granular material; and, unless the bobbin on which
the wire is wound is made of insulating material, it also must be insulated from the
carbon annulus or ring and the granular material.
One of the parts of the segmental annulus or ring is connected to one wire
lead M and the other part is connected to one end of the coil or bobbin of insulated
wire G. The other end of this coil or bobbin of wire is connected to the second
wire lead M'. The leads M, M¹ are in circuit with a suitable source of
electricity.
It will thus be seen that by the above construction an instrument consisting of a
microphone transmitter and electro magnetic receiver is formed in which the
electric circuit is completed from one part of the divided or segmental annulus or
ring through the powdered or granulated carbon to the other part of the said
annulus or ring. If desired of course the two halves or portions of the annulus
and the granulated material may be arranged in series with the primary wire of an
induction coil, the secondary wire of which is in circuit with the coil G and with
the line wire to the distant station.
With this construction of instrument the current is distributed over the entire
area of the annulus and the speaking qualities of the instrument are thereby
increased. The liability of packing of the carbon is
very small.
As before stated the attraction of the magnets on the diaphragm can be readily
varied to suit the requirements of the circuit by adjusting the position of the
core F in the tube E.
Instead of using the L-shaped magnets D Figure 1 we sometimes use a straight
magnet, or two or more straight magnets NN as shown in Figure 6, placed inside
a long cylindrical case and so arranged that their axes are approximately
perpendicular to the plane of the diaphragm or tympan. The ends of the said
magnets nearest the diaphragm are shown furnished with pole pieces N¹, N₁ of
soft iron. When two or more magnetized bars or plates are used, their ends
farthest from the diaphragm are connected by a brass plate N or by a bar or
plate of any suitable non-magnetisable substance. An adjusting screw is
provided at the end of the case and the inner end of this screw engages with the
aforesaid brass plate connected with the magnets. The outer end of the said
screw is furnished with a milled head or other appropriate means for revolving it
so that the position of the pole pieces relatively to the diaphragm can be adjusted.
G, G are coils surrounding the pole pieces. If desired the pole pieces may be
dispensed with in which case the coils would be placed around the edges of the
magnets. The magnets are preferably so arranged that their ends of similar
polarity point in the same direction, the connections between the coils being BO
made that the current will have a like effect upon both poles. The coils G, G and

page_text: the two parts of the carbon annulus may be connected in series as in the instrument
shown in Figure 1 or if desired the coils may be in series with the secondary wire
of an induction coil and with the line wire, the annulus being in series with the
primary wire of said induction coil. For this purpose we have provided four
terminals Q, Q, Q, Q' two of which are joined to the coils G, G and two to the-
different parts of the annulus.
Instead of using straight magnets connected as aforesaid we may use a magnet
or magnets of horse-shoe type, in which case the connections between the coils.
surrounding the poles must be suitably changed seeing that the poles in proximity
to each other are now of opposite polarity.
Instead of using magnets of the forms hereinbefore described various other
forms may be advantageously employed, for example we may use magnets of the
kind illustrated in Figures 11 and 12, or of the kind illustrated in Figure 13. The
former is an incomplete ring R of magnetised steel having affixed to its ends pieces.
of solt iron R' which project toward the centre of the ring and which are furnished
at or near their inner ends with conveniently shaped pole pieces R³ of soft iron,.
bearing bobbins or coils G of insulated wire. The pole picces may be adjustably
or otherwise attached to the inner surface of the pieces R' as illustrated so as to
project into and be surrounded by the ring R, or they may be attached to the outer
surface of said pieces R¹ in which case the bobbins stand out beyond the ring.
The magnet shown in Figure 13 is a complete ring R of magnetised steel, or an
incomplete ring having its ends brought into close proximity to each other. Two
short radial arms R of soft iron extend from opposite sides of the ring nearly to.
the centre thereof, one of these arms being so placed, if the steel ring be not.
complete, as to connect the ends of the ring. Each of the aforesaid arms is bent
up at the inner end upon which is placed a bobbin of insulated wire. Or the arms
may be furnished with adjustable pole pieces bearing the bobbins of wire. The
ring is magnetised in such direction that the north and south poles are at the ends
of the arms R. The bobbins are preferably arranged on the inner side of the soft
iron arms R so that they are surrounded by the steel ring, but they may be
arranged on the other side. In using either of these ring forms of magnet the
carbon annulus, granulated carbon, paper diaphragm, and vibrating diaphragm or
tympan are arranged as before described, the granulated carbon being surrounded
by the steel ring magnet when the pole pieces are attached to the inner surfaces of
the soft iron arms or being supported by it if the bobbins project from the outer
surfaces of the arms. In either case the magnet and arms are insulated from the
carbon annulus and from the granular carbon.
Instead of regulating the distance between the diaphragm or tympan and the
magnet or magnets by adjusting the position of the said magnet or maguets or the
pole pieces of the same we may so arrange the diaphragm that it will be capable
of movement towards or away from the said magnet or magnets.
Or if desired we
may make use of both methods of adjustment in the same instrument. In some
instruments the adjusting devices may be dispensed with.
Instead of dividing the aforesaid annulus in halves as above stated we may
divide it into any suitable number of sections providing the same are connected
electrically to form two groups of sections.
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 a carbon or other suitable annulus divided into
two or more distinct sections which are in electrical connection through a quantity
of carbon or other granules substantially as, and for the purpose, specified.
2. In a telephone transmitter and receiver the segmental annulus in combination
with an adjustable magnet or adjustable core and a stationary coil, substantially as,.
and for the purpose, specified.
3. In a telephone transmitter and receiver two or more straight magnets having

page_text: similar poles in proximity and connected together by a non-magnetisable plate in
combination with an adjusting device engaging with said plate, substantially as
described.
4. A telephone transmitter and receiver_constructed substantially as described
with reference to Figures 1 and 2 or to Figures 6 to 10 of the accompanying
drawings for the purpose specified.
Dated this 17th day of Santamber 1906
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicants.