IMPROVEMENTS IN MICROPHONES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by François Joseph Semal at the Office
of the Commissioners of Patents on the 27th November 1883.
FRANÇOIS JOSEPH. SEMAL of Mons in the Kingdom of Belgium Doctor of
Medicine "IMPROVEMENTS IN MICROPHONES"
My invention relates to an improved construction and arrangement of
microphones which I call simplex microphones.
Upon a suitable plate or flat piece of wood cork ebonite metal or other suitable
material capable of vibrating under the shock of a wave of sound hereinafter
called "the plate" I affix one or several microphonic elements which I call
"simplex" microphonic elements. Each of the said simplex microphonic elements
consists of two small cylinders of hard carbon about three quarters of an inch to an
inch long and a little ball of the same material say of about three eighths to three
quarters of an inch diameter. The said cylinders and ball may be arranged in
various ways according to the position of the transmitter and according to the
number of elements affixed to it. The two small carbon cylinders are glued onto
or otherwise attached to the plate so as to be near each other say from about one
eighth to three eighths of an inch apart and a thin copper wire wound once or
twice found each of the said cylinders puts them in communication one with a
suitable pile (either directly or through the induction wire of an induction coil)
and the other with a suitable telephone receiver provided with its usual automatic
commutator.
The little ball of carbon is placed freely on and between the cylinders and thus
closes the circuits by its tangential points of contact with the two cylinders.
In each particular case different causes contribute to keep the little ball in
contact with the cylinders and at the same time to cause both the points of contact
and the pressure at the points of contact to vary. To produce these effects the
action of gravity may be employed alone or a certain amount of pressure may be
added to it such pressure being produced by the tension of a thin silk thread or
copper wire passed through a hole pierced diametrically through the ball and the
ends of which thread or wire are attached to the top and bottoni of the plate
respectively. Or for the little carbon ball may be substituted a conductor made
also of hard carbon the shape of which is so calculated that by lowering it or by
P

page_text: causing it to bear more or less against the cylinders the number and position of
the points of contact may be increased or diminished at will and here also the
pressure produced by the tension of a thread is applicable. Thus in certain cases
when it is required to regulate at will the sensitiveness of the apparatus a
cylindrical piece of carbon from about three eighths to three quarters of an inch 5
long may be substituted for the carbon ball.
The delicacy of the contacts and the facility with which they may be varied
render the apparatus remarkably sensitive to the waves of sound which strike it
either directly or indirectly through the medium of the vibratory plate upon
which it is fixed it also constitutes really a microphonic element or unit the number 1
and arrangement of which units may vary according to the resistance condition of
the lines the receivers the piles and the like.
Should one microphonic element not be sufficient several of the said elements
may be used upon the same vibratory plate by arranging them either in a
horizontal or vertical line or in the shape of a triangle a lozenge a square or a
circle or other suitable shape and in such cases the cylinders which receive the
are also the cylinders in
current from the pile are connected together as
communication with the telephone that is to say the elements are arranged in
quantity or each cylinder letting out the current from one of the elements is
connected successively to one of the cylinders of the next element taken as the
terminal for letting in the current and so on.
By this arrangement the elements are arranged in series or in tension. The
elements may also be associated in quantity and in tension
When the plate is vertical the two small cylinders are slightly bevilled at the
end by which they are attached to the said plate they thus form with the plate an
angle of about from fifty to eighty degrees. Owing to the inclination of the
cylinders the ball rests not only upon the said cylinders but bears also against the
vibratory plate either directly or through a washer of cork or other suitable
material capable of deadening the trepidation and the shocks of the ball against
the plate or a carbon rest of flat spherical cylindrical or other suitable shape
adhering to the plate may be used for the purpose.
Instead of the carbon cylinders being affixed to the plate by their ends the said
cylinders may be attached to the plate vertically that is to say in the direction of
their length by flattening them on one side and attaching them to the plate by
their flat side the said cylinders being placed a little distance apart say from about
one eighth to three eighths of an inch and the ball is suspended to a thread affixed
to the upper part of the plate and by the action of gravity is kept in contact with
the two cylinders or the thread may be attached by its ends both to the top and to
the bottom of the plate and thus cause the ball to pass more or less against the
said plate.
When it is deemed preferable to place the transmitter horizontally upon a table
the cylinders may be fixed lengthwise upon the plate and small stops attached upon
the said plate to prevent the ball from falling off or a thread attached to the plate
may be used for the same purpose.
Or the ball may be placed between four of the carbon cylinders attached
obliquely upon the plate the said ball thus bearing upon the ends of the said
cylinders which together form an inverted quadrangular pyramid or a sort of
basket. The cylinders at each side of the pyramid are connected together by a
wire conductor one of which leads to the pile and the other to the telephone.
The apparatus is regulated by acting upon its sensitive parts.
The sensitiveness of the apparatus depends upon that of the vibratory plate and
more or less upon its thickness its nature the mode of attachment and the like
Also upon the distance between the cylinders giving more or less stability to th
ball or other conductor in contact with them also upon the weight of the carbo
conductor or ball which has a certain influence upon the 'facility with which th
pressure may be varied at the points of contact also upon the pressure communicate
by the tension thread upon the points of contact and lastly upon the unity c

page_text: action of all the different simplex elements employed. All these conditions may
easily be fulfilled according to the requirements.
It is obvious that the nearer to each other the carbon cylinders are placed the
greater will be the sensitiveness of the microphonic element as then the variations
of the ball's contact will more easily be produced.
The weight of the ball may be varied either by attaching to it a metal mounting
so as not to interfere with the points of contact or by passing through it a more or
less heavy metal pin or in any other suitable manner
As previously stated in substitution for the ball herein before described a heavier
carbon conductor may be used such as a piece of cylindrical carbon about three
eighths to three quarters of an inch long and that end of the cylindrical carbon
which-touches the plate is rounded The tension of the thread may be produced
by means of a screw a pin or other suitable means or for the said thread may be
substituted a rigid metal rod or thick wire screwed at its upper end and upon the
said screwed part of the said rod or wire is placed a screw box which may be
brought nearer to or farther from the ball so as to increase or diminish the pressure
upon it.
To render the microphonic impressions uniform when the elements are grouped
together in quantity the balls or conductors may be connected together by means
of an equalizer that is to say a simple conducting wire or small copper rod passing
through holes in the balls diametrically the said wire or rod being insulated at one
end and by its other end connected to the telephone wire.
The same effect may be produced by means of a carbon or metal rod placed
before the balls so as to form a third support for them.