IMPROVEMENTS IN MEMBRANE TELEPHONES
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
SILVANUS PHILLIPS THOMPSON of University College Bristol in the city and
county of Bristol, Doctor of Science and Professor of Experimental Physics, and
PHILIP JOLIN of 2 Elmdale Rd Redland in aforesaid City and county Engineer do
hereby declare the nature of this our invention for IMPROVEMENTS IN MEMBRANE
TELEPHONES to be as follows:-
Our improvements have for their object the perfection of telephonic instruments
such as are described in the English Mechanic of August 11th 1876 page 551 having
armatures carried on membranes or drum heads, and our improvements are
designed to effect an increase in the sensitiveness and efficiency of the apparatus.
We make our drum-heads in the following manner. We unite together two
membranes after placing between them an armature of clock-spring or of iron,
and, we also in some cases enclose between them a frame which may be square,
hexagonal or any other suitable shape, cut out in metal, ebonite or other non-
absorbent material to support the membranes and stretch them To unite the
membranes we use glue, canada-balsam, or other suitable material. In other cases
we unite two or more menbranes upon a mould which rises or depresses a ridge in
the membranes; this ridge being adapted to fit into a depression in the case of the
instrument. In some cases it is convenient to employ an armature divided into
two or more segments to prevent internally induced currents from circulating. We
press the membranes before the uniting cement is hardened in a mould or die.
After hardening, the drum-head may be impregnated from its under-side with
linseed oil or with stearine or similar material; when very thin membranes are
used we unite four or five of them with linseed oil, or other suitable cement. The
finished drum-head, is placed in a case in front of an electromagnet which we form
of a peculiar pattern. The body of it being curved that it may serve as a handle
for the instrument, one pole serves as a core to receive the coil, and is slit to
provent internal inductions.
To the other pole is attached a Y shaped or C shaped pole piece which beads
round the coil externally but does not completely enclose it.
PHILIP JOLIN,
For the Patentees.

page_text: COMPLETE SPECIFICATION.
We, SILVANUS PHILLIPS THOMPSON, Doctor of Science and professor of Experi-
mental Physics of University College Bristol and PBILIP JOLIN 2 Elindale Koad,
Redland Bristol, Engineer do hereby declare the nature of our invention for
"IMPROVEMENTS IN MEMBRANE TELEPHONES" and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement:-
Our Improvements. relate to telephonic instruments such as are described in the
English Mechanic of August 11th 1876 page 551 that is to say instruments having
armatures carried on or by membranes or drumheads and the said improvements
are designed to increase the sensitiveness and efficiency of such instruments or
apparatus.
In constructing telephones of this kind according to our improvements we use a
compound diaphragm or drum head made by placing between two membranes an
armature formed of magnetic material such as a piece of clock spring or of iron
membranes are usually kept taut by stretching and tying down over or around
a circular aperture. According to our improvements we in some cases enclose
between the membranes a light frame which may be square hexagonal or of other
suitable shape and formed or cut out of metal, ebonite, or other non absorbent
material, this frame assists in straining or stretching and supporting the mem-
brane and renders it so stiff that the tying down may be dispensed with in
fact the compound drumhead may be used without stretching in very much the
same way as a metallic plate is used. We unite the said membranes by means of
gluc, canada-balsam or other suitable cement. In some cases we unite and
stretch two or more membranes by means of a mould which forms around the
combined membranes a circular ridge or corrugation adapted to fit into a channel
or depression in the case of the instrument and to be held by and between this
channel and a corresponding projection on the cover. This method also further
dispenses with the necessity of tying down. We press the membranes before the
uniting cement is hardened into the mould or die. After the hardening of the
drumhead it may be impregnated from its under side with linseed Oil stearine or
similar material. When very thin membranes are used we unite a number say four
or five of them with linseed Oil or other suitablo cement. In some cases we employ
an armature divided into two or more separate segments to prevent the circulation
therein of internally induced currents.
The drumhead or diaphragm prepared in the above manner being ready for use
is placed in a case in front of an electro magnet of peculiar form or construction as
hereinafter described.
Our improvements are illustrated in the accompanying Drawing.
Figures 1, 2 and 3 shew the drumheads formed of membranes enclosing an
armature as above described.
Figures 4, 5 and 6 illustrate the peculiar formation of the electro magnets.
Figure 7 shews in vertical section an instrument constructed according to our
Invention.
A is the case or box of the instrument and B is the cover.

page_text: a is the drumhead formed of the united membranes, b is the armature enclosed
therein as above described. The aforesaid frame of metal or other material
enclosed between the membranes to support and stretch them is shewn at c.
At d we have shewn the edge or corrugation formed as above described around
the drum head and fitted in the channel formed round the box of the instrument
wherein it is securely held by the cover B.
In figure 3 the armature is shewn divided into Sections for the purpose above
specified.
The body e of the electro magnet is preferably curved as shewn so that it may
serve as a handle for the instrument. One pole serves as a core c¹ to receive the
coil and is slit to prevent internal inductions. To the other pole is attached a
Y shaped or C shaped pole piece e³ which is bent around but does not completely
enclose the coil.
The construction and arrangement of these pole pieces is clearly shewn in
Figure 6.
Having now particularly described and ascertained the nature of our said
Invention and in what manner the same is to be performed we declare that what
wo claim is
First: The diaphragm or drumhead composed of united membranes enclosing an
armature and a frame whereby they are stiffened and strained as and for the purpose
specified.
Second-The diaphragm or drumhead composed of united membranes.enclosing
an armature and having the membranes stiffened and strained by pressure in a
mould while the cement sets or hardens as and for the purpose spocified.
Third In combination with a membrane diaphragm or drumhead an attached
armature slit or divided into sections as and for the purpose specified.
Fourth-The electro magnet with pole pieces constructed and arranged
relatively to the coil or bobbin as hereinbefore described.
Fifth The improved telephone Instrument herein before described and illus-
trated by the drawings annexed.
Dated this 19th day of March 1885