Improvements in Microphones.
Year: 1891

page_text: Date of Application, 27th Aug., 1891
Complete Specification Left, 28th Apr., 1892-Accepted, 28th May, 1892
PROVISIONAL SPECIFICATION.
[Communicated from abroad by Messrs. SIEMENS & HALSKE, of Berlin, in the
German Empire, Electrical Engineers.]
Improvements in Microphones.
We, SIEMENS BROTHERS & Co. LIMITED of 12 Queen Anne's Gate,
Westminster in the County of Middlesex, Electrical Engineers, do hereby declare
the nature of this invention to be as follows: :-
Microphones have heretofore in some cases been constructed with a diaphragm
having at its centre a fixed carbon plate which bears against the flat base of a
conical carbon block, the conical surface of which is carried in a correspondingly
coned recess in a fixed block of metal or other conducting or non conducting
material, the cone being free to rotate in the recess. By a rotation of the parts
round the central axis, new points of contact are obtained between the carbon plate
of the diaphragm and the base of the conical block.
This arrangement is subject to the disadvantages, on the one hand, that the
conical carbon block must be very accurately constructed, whereby the microphone
becomes too expensive, and, on the other hand, that when the carbon surfaces
become worn, the pressure with which the contact surfaces bear against each other
becomes gradually reduced resulting in a deterioration of the sound transmitted.
The present invention relates to an improved construction of the above described
form of microphone whereby the above mentioned disadvantages are obviated.
For this purpose the diaphragm has a fixed carbon plate, and is made rotatable
together with the mouth piece, as before, but in place a single central carbon cone,
resting in a coned cavity of a. fixed block, as before, we employ two or more, by
preference three, carbon cones, arranged symmetrically round the central axis of
the instrument, and resting in a corresponding number of coned cavities in a metal,
carbou, or other plate carried by a very flexible disc of metal foil, paper or woven
fabric fixed at its circumference to the casing. At the rear of this disc is an
adjustable helical spring pressing it forward or upward with a certain elastic
pressure so as to cause the flat bases of the carbon cones to bear against the carbon
plate of the mouth piece diaphragm with a corresponding pressure.
The diaphragm is fixed to the mouth piece and its edge projecting beyond the
latter is rotatably confined beneath a metal ring fixed to the microphone casing, 80
that by turning the mouthpiece and diaphragm, the contact surfaces between the
carbon plate and the bases of the cones can be changed.
The spring that presses the cones against the diaphragm plate rests by preference
with its rear end in a cap screwed into the rear of the casing, so that by turning
Buch cap in one direction or the other, the pressure of the spring can be accurately
adjusted, and thus any wear between the carbon contact surfaces can be com-
pensated for. The metal or other plate carrying the carbon cones, is connected
by a flexible wire to the one lead of the circuit attached to the microphone casing,
the other lead being fixed to the metal ring which is in conducting contact with the
diaphragm,
Although it is preferred to make the above described carbon pieces and their
seats in the supporting plate of conical form, yet these parts may also be made of
other configuration.
Dated this 27th day of August 1891.
ABEL & IMRAY,
Agents for the Applicants: .

page_text: COMPLETE SPECIFICATION.
Improvements in Miorophones:
We, SIEMENS BROTHERS & Co. LIMITED of 12 Queen Anne's Gate,
Westminster in the County of Middlesex, Electrical Engineers 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:-
Microphones have heretofore in some cases been constructed with a diaphragm
having, at its centre a fixed carbon plate which bears against the flat base of a
conical carbon block, the conical surface of which is carried in a correspondingly
coned recess in a fixed block of metal or other conducting or non-conducting
material, the cone being free to rotate in the recess. By a rotation of the paths
round the central axis, new points of contact are obtained between the carbon plate
of the diaphragm and the base of the conical block.
This arrangement is subject to the disadvantages, on the one hand, that the
conical carbon block must be very accurately constructed, whereby the microphone
becomes too expensive, and, on the other hand, that when the carbon surfaces
become worn, the pressure with which the contact surfaces bear against each other
becomes gradually reduced, resulting in a deterioration of the sound transmitted.
The present invention relates to an improved construction of the above described
form of microphone whereby the above mentioned disadvantages are obvinted.
For this purpose the diaphragm has a fixed carbon plate, and is made rotatable
together with the mouth piece, as before, but in place of a single central carbon
cone, resting in a coned cavity of a fixed block, as before, we employ two or more,
by preference three, carbon bodies of conical' or other form arranged symmetrically
round the central axis of the instrument, and resting in a corresponding number of
coned cavities in a metal, carbon, or other plate carried by a very flexible disc of
metal foil, paper or woven fabric fixed at its circumference to the casing. At the
rear of this disc is an adjustable helical spring pressing it forward or upward with
a certain elastic pressure so as to cause the flat bases of the carbon cones to bear
against the carbon plate of the mouth piece diaphragm with a corresponding
pressure.
Fig. 1 of the accompanying drawing shews a vertical section, and Fig. 2 an
elevation of the disc sand plate 61 of the improved microphone.
The diaphragma is fixed to the mouth piece S and projects with its outer
periphery beneath the metal ring R fixed to the casing, so as to be rotatable with
the mouth piece; to the diaphragm is fixed the carbon plate band against this
bear the bases of carbon cones C C C³, preferably three in number as shewn.
These cones enter correspondingly formed holes in a carbon or metal plate 6' which
is attached to a discs of very flexible material, such as metal foil, paper or woven
fabric; secured at its circumference to the casing G.
+
A springbears with its one end against the plate band at its other end against
a screw cap by means of which it can be made to press with a regulated pressure
upon the plate 6 thus regulating the closeness of contact between the cones C¹ C³°C'
and the plates b and b¹.
On rotating the mouth piece S diaphragm a and plate b, this will slide on the
bases of the cones, thus bringing fresh portions of its surface in contact with the
lätter.
A conducting communication is established between the plate and the line
wire L by means of the flexible wire d', while the communication between band
the line wire L is established by means of the ring R to which L' is attached and
with which a is in sliding contact.
It will be evident that the bodies C¹ C² C' may be varied both as to form and
number.

page_text: 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
we claim is :
A microphone wherein carbon bodies of conical or other form bearing against
the carbon plate of the diaphragm, are supported in a yielding or flexible manner
by a plate or block carried by a flexible diaphragm attached to the casing, in
combination with an adjustable pressing device for maintaining the required degree
of contact between the carbon bodies and the said supporting plate or block,
substantially as and for the purposes described.
Dated this 28th day of April 1892.
A-BEL & IMRAY,
Agents for the Applicants.