Improvements in Telephone Receivers, Transmitters, and Silent Closets.
Year: 1894

page_text: Date of Application, 14th Sept., 1894
Complete Specification Left, 13th July, 1895-Accepted, 17th Aug.. 1895
PROVISIONAL SPECIFICATION.
Improvements in Telephone Receivers, Transmitters, and Silent
Closets.
I, FREDERICK HERBERT WILLIAM HIGGINS, of 17 and 18 Cornhill in the
City of London, Electrician, do hereby declare the nature of this invention to be as
follows:-
:―
In order to increase the volume of sound emitted whilst at the same time
maintaining clearness of articulation I construct the receiver in the following
manner :-
To prevent reciprocal vibration of the case under the influence of powerful
vibrations of the diaphragm I make the case of a non-metallic rigid material, such
as slate and sufficiently massive to prevent its responding to vibrations of the
diaphragm, upon which consequently the energy of the electrical undulations are
concentrated.
The diaphragm of the receiver I make many times the thickness and more than
twice the diameter of the diaphragm usually employed. I make the diaphragm not
of one piece bat build it up of two thicknesses of iron cemented together with
shellac and with an outer covering of cardboard also cemented on; and in this
diaphragm I form a radial slit extending from the centre to the circumference.
I mount the diaphragm on a slab of slate or like non-metallic rigid material, so as
to close a cavity therein from whence there leads out at a point opposite to the
centre of the diaphragm a flexible listening tube, terminating in a suitable ear
piece.
1 arrange several permanent magnets each with one of its poles close to the
circumference of the diaphragm and these magnets at their other ends are all
connected with a pole piece which faces the centre of the diaphragm. This pole
piece carries the bobbin with windings of insulated wire forming part of the line
circuit. The arrangements which I have described adinit of the use of a bobbin of
large diameter with many convolutions of wire.
In order to diminish electrostatic retardation I wind the bobbins of the receiver
in two parts in opposite directions, in the way described in my Specification
No. 16991 in the year 1891 in respect to the winding of certain electro-magnets
therein referred to.
To suppress or reduce feeble irrelevant sounds when this is found to be necessary
I form the inner surface of the listening tube for a short portion of its length with
velvet or some such material suitable to check air vibrations.
The transmitter I mount on a thick slate base carried by pillars which separate
it from the back board or other support; in this way I avoid the reverberation
which occurs when the transmitter is mounted in a box.
The primary and secondary of the induction coils I also wind each in two parts
as in the case of the receiver bobbin.
The silent closets which are often provided to contain telephones are difficult to
ventilate because any opening provided to admit air admits sound also.
I overcome
this difficulty by lining the ventilating passages with velvet or like material.
Preferably provide a curved ventilating pipe rising from the roof of the silent
closet and this I line with velvet covering the whole of the interior therewith. A
similar ventilating pipe I may provide to admit air to the lower part of the closet.
Dated this 14th day of September 1894.

page_text: Improvements in Telephone Receivers, Transmitters, and Silent
Closets.
J, FREDERICK HERBERT WILLIAM HIGGINS, of 17 and 18 Cornhill in the
City of London, Electrician, 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 order to increase the volume of sound emitted whilst at the same time
maintaining clearness of articulation I construct the receiver in the following
manner :-
To prevent reciprocal vibration of the case under the influence of powerful
vibrations of the diaphragm 1 make the case of a non-metallic rigid material, such
as slate and sufficiently massive to prevent its responding to vibrations of the
diaphragm, upon which consequently the energy of the electrical undulations are
concentrated.
The diaphragm of the receiver I make many times the thickness and more than
twice the diameter of the diaphragm usually employed. I make the diaphragm
not of one piece but build it up of two thicknesses of iron cemented together with
shellac and with an outer covering of cardboard also cemented on; and in this
diaphragm I form a radial slit extending from the centre of the circumference.
I mount the diaphragm on a slab of slate or like non-metallic rigid material, so as
to close a cavity therein from whence there leads out at a point opposite to the
centre of the diaphragm a flexible listening tube, terminating in a suitable ear
piece.
I arrange several permanent magnets each with one of its poles close to the
circumference of the diaphragm and these magnets at their other ends are all
connected with a pole piece which aces the centre of the diaphragm. This pole
piece carries the bobbin with windings of insulated wire forming part of the line
circuit. The arrangements which I have described admit of the use of a bobbin of
large diameter with many convolutions of wire.
In order to diminish electrostatic retardation I wind the bobbins of the receiver
in two parts in opposite directions, in the way described in my Specification
No. 16991 in the year 1891 in respect to the winding of certain electro-magnets
therein referred to.
To suppress or reduce feeble irrelevant sounds when this is found to be necessary
I form the inner surface of the listening tube for a short portion of its length with
velvet or some such material suitable to check air vibrations.
The transmitter I mount on a thick slate base carried by pillars which separate
it from the back board or other support; in this way I avoid the reverberation
which occurs when the transmitter is mounted in a box.
The primary and secondary of the induction coils I also wind each in two parts
as in the case of the receiver bobbin.
The silent closets which are often provided to contain telephones are difficult to
ventilate because any opening provided to admit air admits sound also. I overcome
this difficulty by lining the ventilating passages with velvet or like material.
Preferably provide a curved ventilating pipe rising from the roof of the silent
closet and this I line with velvet covering the whole of the interior therewith.
A similar ventilating pipe 1 may provide to admit air to the lower part of the
closet.
In order that my invention may be fully understood and readily carried into effect
I will preceed to describe the drawings annexed.
Figures 1 and 2 relate to the receiver.

page_text: Figures 3 and 4 relate to the method of mounting the microphone transmitter.
Figure 5 relates to the means for ventilating the silent closet.
Figure 1 represents a section of my telephone receiver. a is a slab of slate or
like material forming the base of the instrument, it has a cavity a¹ in it from whence
at a the listening tube or tubes lead off. is the diaphragm which I construct as
follows: The face next to the slab or portion a of the case is of cardboard say one
thirtieth of an inch thick and over it are two discs of thin sheet iron say each one
sixtieth of an inch thick, the three are cemented together with shellac solution,
making a compound diaphragm say barely one twelfth of an inch thick. The
diaphragm is slit radially from centre to circumference, the slit may be one twentieth
of an inch wide. It is advisable to slit the several discs before cementing the parts
together, as all roughness or distortion at the edges of the slit must be avoided.
e is the other portion of the case, it is also preferably of slate; the two parts a and e
are held together by screws which also pass through the edges of the diaphragm
and so the diaphragm is nipped and held between the parts a and c. Upon the
part can iron back d is fixed by screws and e is a core of soft iron screwed into d
and secured by a lock nut. The core is tubular as is indicated by dotted lines and
it can be adjusted to set its face at a suitable distance from the diaphragm.
core e is slit longitudinally to prevent electric currents circulating around it. ff are
bent bar magnets say eight in number, they are each fixed by one end to the iron
back d and their other ends are ranged at equal distances apart around the edges of
the diaphragm b. The magnets conspire to produce opposite polarities in the core
and the diaphragm and the magnetic circuit is complete through metal excepting a
narrow air gap or gaps. Figure 2 is a transverse section of one of the magnets f.
The bobbin of insulated wire g is connected in the line circuit, under ordinary
conditions this bobbin may be wound to a resistance of 100 units. The core e
passes freely through the bobbin and the latter is attached to the part of the case
by small screws g¹ g¹.
The
The bobbin is wound in the usual way until it is half full and then the direction
of winding is reversed. When the bobbin is full the two windings are so connected
that the passage of a current may be traced as follows:-From a line terminal to
the coils next to the core and progressively outwards until the middle of the
winding is reached; then to the external coils and from these progressively inwards
to the middle of the winding; here the wire is led out and connected with the other
line terminal. I prefer to provide two flexible listening tubes branching off from a²
and near their outer ends I line these tubes for a length of three or four inches
with velvet, so that the pile of the velvet projects inwards. Also I may provide
ferrules of polished metal which I can insert more or less into the velvet lined
portion of the listening tube to regulate the extent to which the feebler sounds
shall be obliterated.
When a speaking tube is used in connection with the transmitter I apply to it a
like arrangement. An ordinary speaking tube is found to produce a muffled sound,
this I avoid by providing upon the speaking tube, at a short distance from the
mouth piece, a branch a few inches long open at its end and this branch, in order
to prevent the escape of sound, I line with velvet in the manner already
described.
Figures 3 and 4 show the way in which I mount the transınitter. h is the
supporting board carrying, it may be, the call bell and other parts of the telephone
equipment. ii are four metal pillars supporting the slate slab k; the microphone
transmitter is fixed upon this slab. An ordinary mouth piece is shown in this
figure but a speaking tube may be applied.
The induction coils used in connection with the transmitter are constructed in the
usual manner except that I wind them in the manner already explained in respect
to the receiver coil, that is to say, if the primary coil consists of two layers, I first
wind one layer in one direction and over it the second layer in the contrary direction
and I connect the layers in series. Then I wind over the primary half of the
secondary coil in one direction and the other half in the contrary direction and

page_text: F. H. W. HIGGINS.