Year: 1896

page_text: This Print is in accordance with the Original Specification as it stands after
Amendment (under Section 18 of the Patents, &c. Act, 1883) as allowed by
the decision of the Comptroller General of the 25th day of October 1898.
Date of Application, 3rd Nov., 1896
Complete Specification Left, 3rd Aug., 1897-Accepted. 3rd Jan., 1898
I, THOMAS JAMES HOWELL, of 43, Millais Street, Albany Road, Camberwell Road;
in the County of London, Engineer, do hereby declare the nature of this invention
to be as follows:-
This invention relates to microphones, and iny present improvements, such as
hereafter described, enable me to produce an instrument of increased sensitiveness
and capable of being used with a current of either high or low power as may be
desired without damage to the microphone or any part thereof, and, further, by the
use of iny invention, the microphone remains equally sensitive at all times, and does
not require shaking or re-adjusting at intervals as is so common with many such
instruments now in use.
The essential feature of my present invention consists in introducing between the
two carbon plates (or equivalents) a honeycombed or cellular disc of suitable thick-
ness, so that the granulated carbon (or equivalent) contained therein may not be able
to fall down and wedge itself against the vibrating plate but on the other hand may
remain spread against the surface of the same.
I therefore construct my improved microphone or transmitter in the following
manner.
I make a box of hard wood or any other insulating or properly insulated material,
having a removeable lid with central hole forming the mouthpiece of the microphone.
I fix two terminals (or inore if desired) preferably at the rear of the box, one (or
more) being connected with a metal spring projecting upwardly, within the centre of
said box, and the other (or others) being connected to a brass or other metal ring
secured upon the rabbet or edge of the box over which is to be passed the lid. By
preference, I make the connection to the said ring at, say, three points equally
distant apart by means of three wires of equal resistance, my object being to
centralize the speech or to balance the current and fluctuations equally around the
centre of the instrument. Similarly, I may find it advantageous to employ more
than the one spring aforesaid within the box at its rear.
The honeycombed or cellular disc aforesaid may be cut or stamped from a sheet
of ebonite one quarter of au inch in thickness or thereabouts. I may however
employ other material instead of ebonite, but, preferably, of an insulating nature.
The disc may be either punched or drilled over the whole of its surface completely
through its thickness, so as to form a number of cells of any convenient shape, the

page_text: outer ends of each cell being widened out into cone shaped mouths for the purpose
hereafter described.
My improved microphone is built up as follows. First within the box and upon
the projecting spring or springs, I lay a disc of carbon, a ring of felt or other soft
yielding substance being previously inserted. Upon said disc, I now lay the honey-
combed or cellular disc and fill the holes or cells with carbon granulated to a
particular size of grain. The edge of the honeycombed or cellular dise will now lie
on a level with or come slightly above the brass ring or rabbet of the box, and upon
it I lay the final dise of thin carbon which is to form the vibrating diaphragm, but
sufficient space must be provided to allow of this movement, such as laying a ring
of thin paper upon the cellular disc or leaving its extreme edge slightly raised, the
space however not being so large as to allow the grains of carbon or the like to fall
down between the honeycombed or cellular disc and the said carbon disc. Finally
the lid or mouthpiece is screwed or wedged on the box over the thin carbon disc, a
ring of felt, rubber or the like being provided so as to prevent said disc from
accidentally breaking under the pressure.
As already mentioned, a microphone, constructed on the foregoing lines will be
found much more effective and durable than those in present use, the effect of the
honeycombed or cellular disc being to preserve an evenly conducting medium. The
rear carbon disc, too, bearing against a spring as described, instead of against an
unyielding connection, is capable of a certain amount of vibration with the front disc
or diaphragm. The object of the conical formation of the mouths of the cells is to
cause the grains to fall of their own weight until they bear lightly against the carbon
disc or diaphragm, and when the latter is being used they will rise and fall and be
constantly agitated in proportion to the amplitude of vibration of the disc or diaphragm.
It will be obvious, however, that instead of making the cells aforesaid with conical
mouths, I may attain the desired purpose by inserting therein small tubes of silk,
rubber or the like, projecting slightly from the honeycombed or cellular disc so as
to lightly touch the vibrating carbon diaphragm, thus permitting the granulated
carbon (or equivalent) to be held sufficiently against the diaphragm without impairing
the latter's vibratory powers. As another alternative, I might cover the front surface
of the honeycombed or cellular dise with fine cotton wool, excepting at the opening
of each hole.
Various other modifications may be adopted, such as a number of separate small
tubes packed together and filled with carbon in place of the honeycombed or cellular
disc aforesaid, without departing from the essential feature of my invention.
Dated this 2nd day of November 1896.
STANLEY POPPLEWELL & Co.,
Agents for the Applicant.
I, THOMAS JAMES HOWELL, formerly of 43, Millais Street, Albany Road, Camberwell
Road, in the County of London, now of 70, Farringdon Road, in the County of London,
Engineer, 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 :-
This invention relates to microphones, and my present improvements, such as
are hereinafter described, enable me to produce an instrument of increased
sensitiveness and capable of being used with a current of either high or low power as

page_text: may be desired without damage to the microphone or any part thereof, and further by
the use of my invention, the microphone remains equally sensitive at all times, and
does not require shaking or re-adjusting periodically, as is so common with many
microphonic instruments now in use.
One feature of my present invention consists in introducing between the two carbon
plates, or equivalent plates, a honeyconbed or cellular disc or block, or a modification
thereof, of suitable thickness, so that the granulated carbon (or its equivalent)
contained therein is prevented from falling and wedging itself against the vibrating
plate or tympan, but on the other hand may remain in contact with the surface of the
same, and thus ensure at all times a reliable and properly distributed contact for
producing the necessary fluctuations of the electric current.
I therefore construct my improved microphone or transmitter in the following
manner, and as shown by the accompanying drawings, to which I will hereinafter
refer.
In said drawings, Figure 1 is a section taken through the thickness of my
transmitter, and Figure 2 is a plan of the interior of the box portion thereof.
Figures 3 to 8 illustrate some modified forms in which the honeycombed or cellular
dise may be made, and Figure 9 shews the position of the carbon granules in a
single cell (enlarged), the mouth of which is countersunk or coned.
In carrying out iny invention, I make a box A of hard wood or any other suitable
insulating or properly insulated material, having a removable cover B with central
hole C, forming the mouthpiece of the inicrophone or transmitter.
I fix two terminals D and E (or more if desired) preferably at the back of the
box, one D (or more) being connected with a metal spring F projecting inwardly
towards the centre of the said box A, and the other E (or others) being connected to
brass or other conducting metal ring & secured upon the rabbet or edge of the box A
over which is screwed the cover B. By preference, I make the connection to the said
ring G at more than one point, say for instance, three points ggg equally distant
apart by means of three wires e e e of equal resistance, connected to a common wire e¹
leading to the terminal E, my object being to centralize the speech by causing the
fluctuating electric current to be distributed as equally as possible over the carbon
electrode J. Similarly, 1 may find it advantageous to employ more than the one
central spring F aforesaid, within the box at its rear, or it may be possible to dispense
with any such spring, employing instead thereof, a rigid connection, such as a metal
ring or block.
The honeycombed or cellular disc aforesaid, may be cut or stamped from a sheet of
ebonite or other material of any suitable thickness, whether cut or moulded, but
preferably of an insulating nature, or the disc may be built up of two or more layers
of various materials. I find in practice that an efficient form of disc may be
constructed as shown in Figure 1, the ebonite or non-conducting portion of which, H,
lies against the inner carbon or equivalent plate J, and may be held thereto by any
suitable means such as a strip of paper secured around the edge. The disc H may be
either punched, drilled or moulded with holes distributed over the whole of its surface
passing completely through its thickness and also partly into the thickness of plate J
so as to form a number of cells K K K K of convenient diameter and shape, each
intended to contain a number of specially prepared carbon granules, screened to the
minimum size, large enough to prevent their falling down between the cellular disc and
the carbon vibrating plate or tympan L.
My improved microphone is built up as follows.
Within the box A and upon the projecting spring or springs (or upon a rigid
metal block or ring where such is used in place of spring or springs F) I lay the
honeycombed disc with the carbon face J inwards, a ring of felt or other soft yielding
substance being previously inserted if necessary or desired. I now fill the holes or
cells K K with granulated carbon, or any equivalent thereof. The face of the honey-
combed or cellular disc H will now lie on a level with or come slightly in front of the
metal ring G or rabbet of the box, and upon said ring I lay the final plate L of thin
carbon or equivalent, which is to form the vibrating diaphragm or tympan, but

page_text: sufficient space must be provided between the mouths of the cells K K and the
plate L to allow of this vibration, for which purpose a ring of paper may be laid upon
the cellular disc H or the latter may be left slightly raised around its extreme edge.
It is important, however, that this space be not so large as to allow the grains of
carbon or the like to fall down between the honeycombed or cellular disc H and the
said carbon plate L. Finally the cover or mouthpiece B is screwed or wedged on the
box A over the thin carbon plate L, a ring M of felt, rubber or the like being provided
so as to prevent said plate from accidentally breaking under the pressure.
I will now proceed to describe shortly a few of the modified forms which the honey-
combed or cellular disc may take. In Figure 3 is shown a disc H, made preferably
of ebonite, hard wood, or non-conducting or only feebly conducting material, punched,
drilled or moulded through its thickness with a number of holes K K forming cells
for containing loose carbon or equivalent, the latter forming the electrical connection
between the vibrating plate and the back or inner plate of carbon J, which may
either be separate from or cemented or otherwise attached to said honeycombed
disc H. In another form I may have the carbon or equivalent plate J, Figure 4,
sufficiently thick, say one quarter of an inch or more, for the holes K K to be con-
tinued into the same without extending right through, a larger contact area being
thus provided for the innermost carbon granules of each cell. The cells are showi
rounded at the end in Figure 4, and square in Figure 1. The said carbon or equivalent
plate J may, however, if preferred, be in two thicknesses or layers, the outside layer
being solid, and the inner layer, adjacent to the non-conducting honeycombed disc, being
perforated so as to register therewith.
I may find it advisable for some purposes, to provide each cell K K, Figure 5, with
a small accurately fitting open tube N of silk, rubber, or other equivalent material,
projecting forwardly so as to touch or nearly touch the vibrating plate or tympan L,
the outerinost carbon or equivalent granules being supported upon the projecting
ends of said tubes N N, and thus being held sufficiently against the diaphragm
without impairing the latter's vibratory powers. An equivalent manner of treating
the honeycombed disc would be to coat its face with some sticky substance and cover
it with cotton wool chippings or other fluffy material O, or otherwise cover it except
at the opening of each cell, as indicated by Figure 6.
Figures 7 and 8 show a broken plan and section respectively of another form of my
honeycombed disc, being a single disc of carbon or equivalent perforated through
from back to front with plain cylindrical passages or cells K K, and painted or coated
over its outer face with shellac or other insulating substance.
Figures 7 and 84 are similar views of a disc, the cells K K of which are counter-
sunk or widened out into cone shaped mouths. Figure 9 shows an enlarged section
of one of these cells, the object of the conical formation of the mouths being to
cause the granules to slide or fall of their own weight until they bear lightly against
the carbon diaphragm L. When the microphone is being used, the granules will
receive the impulses, and be constantly agitated in proportion to the amplitude of
vibration of said diaphragin or tympan L.
Various other modifications may be adopted, such as a number of separate small
tubes packed together and filled with carbon in place of the honeycombed or cellular
disc aforesaid, without departing from the spirit of my invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is:-
1. In a microphone which contains an inner carbon disc or block such as J or its
equivalent, the employment of a spring or springs such as F, or a spiral or any
other form of spring, situated substantially as described in the foregoing
specification.
2. In a microphone, the employment of a brass or other conducting ring upon the
rabbet or edge of the box upon which is applied the vibratory diaphragm ör tympan

page_text: the connection being made to said ring from the terminal at more than one point in
the manner and for the purpose specified in the foregoing specification.
3. The improved microphone substantially as herein before described with reference
to the accompanying drawing Fig. 1.
CA 1907
STANLEY, POPPLEWELL & Co.,
7 & 8, Southampton Buildings, Chancery Lane, London,
Chartered Patent Agents.
Agents for the Applicant.