An Improved Microphone.
Year: 1893

page_text: Date of Application, 11th Apr., 1893-Accepted, 24th June, 1893
COMPLETE SPECIFICATION.
[Communicated from abroad by CHARLES MILDE, SON AND COMPANY, 26, Rue
Langier, Paris, Electricians.]
An Improved Microphone.
I, HENRY HARINGTON LEIGH, Assoc. M. Inst. C.E., Fel. Ch. Inst. P.A.,
Fel. I. Inst., practising as Phillips & Leigh, of No. 22, Southampton Buildings,
Chancery Lane, in the Administrative County of London, Engineer and Chartered
Patent Agent, 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 an improved microphone, and the object of it is to
produce a microphone which shall be characterised by great simplicity of construc-
tion and by a capacity for being used in either a short or a long distance telephone.
This latter faculty is due to its marked sensibility in respect of the transmission of
the vibrations.
In order that the invention and the means by which it is to be carried into
practical effect may be thoroughly understood, I will describe it and them in detail,
referring in so doing to the accompanying drawing which is to be taken as part of
this Specification and read therewith.
The drawing in question is an illustration, by way of vertical section, of one of
the forms in which the present invention can be embodied, but it is to be distinctly
understood that the invention is not limited to the arrangement of parts illustrated,
inasmuch as that arrangement may be varied to any extent without departing from
the invention, provided that the construction adopted is based upon the principles
hereinafter specified.
A is a part of the vibratory diaphragm. The microphone is held to the latter
by a small nutted screw made fast to a metallic cap C. The latter is provided
with a second and binding screw by which the circuit wire is connected to it.
Between the closed end of the said cap and the diaphragm there is interposed
a washer or packing ring D of cork. The microphone proper is inserted in the
cap in which it is held by simple mechanical contact. It consists of two circular
shells E made of thin metal and corrugated as to their faces. These shells
together form a flat drum. This latter is filled for about of its capacity with
chemically sifted and purified grains of coke or carbon or other semi conducting
substance. A carbon rod F is inserted in a nozzle which projects centrally from
each side of the drum. These rods are insulated from their respective nozzles
and the drum by paper rings G. They are therefore in intimate contact with
the semi-conducting substance in the drum.
To increase their sensibility to the vibrations of the instrument, the two rods
are hollowed axially from their respective bases and the cavities filled with
lead. A small cap or washer corresponds with the one C of the diaphragm
and is provided with a small binding screw to which the circuit wire can be
connected.
The above is a description of one way in which the improved microphone
which forms the subject of the present invention is put into practical
form, and now it must be repeated that the invention is not limited to the
construction illustrated and just described. The lead plugs in the carbon rods
are simply weights combined with one, or with both carbons if necessary. They
may be made of any other heavy substance. They may be made in the form
of rings surrounding the carbons or in the form of washers and be placed in
the closed ends of the caps C and I, or the latter may be made stronger. In
short neither the shape nor the material of the plug is part of the invention

page_text: which is characterised by the combination of a weight with either or both the
carbon rods of the microphone.
Instead of fixing the microphone to the vibrating diaphragm by a screw,
be cemented thereto with any suitable cement.
The insulating materials may be of any suitable material.
it may
The wires, instead of being connected by binding screws, may be wound round
carbons inserted between the caps and the carbons or by any other suitable
means.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
An improved microphone consisting of a drum or box filled in part with purified
grains of coke, and made by the combination of two thin metal sheets corrugated
on their faces through the centre of each of which projects a carbon rod furnished
with a weight, one of the rods being fixed to the transmitting diaphragm.
Dated this 11th day of April 1893.
HENRY H. LEIGH, C.P.A.