Year: 1886

page_text: Date of Application, 1st Dec., 1886.
Specification Accepted, 5th Jan., 1887.
We, THOMAS WALLACE of 316 West 60th Street and OSCAR A. EN HOLM of
117 East 112th Street, both of the City, County, and State of New York, United States
of America, 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 :-
Our invention relates to microphones and has for its object to improve the construc-
tion of such instruments and to render them cheap, simple, and effective, and at the
same time more delicate and of greater capacity with the least liability of getting out
of adjustment, and to these ends our invention consists in a microphone constructed
substantially as hereinafter pointed out.
Referring to the accompanying drawings forming part of this specification for a
more particular description :-
Fig. 1 is a plan view of one form of a microphone embodying our invention.
Fig. 2 is a side view of the same.
Fig. 3 is a cross section of Fig. 1.
Figs. 4 and 5 are modified forms.
Our
Many attempts have heretofore been made to construct microphones that shall be
effective and practical, but they have been subject to more or less objections either in
regard to delicacy of operation under all conditions or expense of manufacture.
object has been to construct a microphone that is simple and cheap, and not liable to
get out of order and at the same time be capable of transmitting all kinds of sounds
from the faintest whisper to the loudest talking without mutilating the sounds and
without adjustment of the parts.
In carrying out our invention any sort of a can or box may be used to support the
working parts, and we have shown in the drawing these latter parts only as they can
be applied to the case in any well known manner. We use a diaphragm A, of any
suitable material without regard to its structure or thickness as we have found that
any kind will work from a thin sheet of paper-board to a thick piece of wood.
Upon this diaphragm we mount a bridge piece B, of any suitable non-conducting
material such as wood, rubber, and the like, which is tapered or slopes to one end,
and this end is secured at or near the edge of the diaphragm, while the other end rests
upon a foot piece b², which is secured to the centre of the diaphragm. The bridge

page_text: piece may be conveniently secured in this position by glue, mucilage &c. and is
preferably made in one piece.
The face of the bridge is grooved at c, c, to receive the bars of carbon or electrodes
C, C, which may be secured in any manner, as by glue. These bars C, C, are each
connected to one end of the line wire h, h, one portion of which goes to the distant
station, while the other is connected to the ground or in any other usual way, the
battery being interposed directly in the line at any desired locality. The terminals of
the line wire are connected to the ends of these pieces C, C, by solder or by being
wrapped around the end or any other equivalent manner that will give good electric
contact.
Upon these bars is placed a bar D which rests loosely thereon and is suspended by
a fine cord from the pin or screw d, or held up by means of a supporting pin as shown
in Fig. 4. This bar or electrode is weighted at one end, as at D¹, by boring the same
and inserting some heavy metal, as lead. The bar D thus rests lightly upon the
bars C, C, and forms the connecting link between the latter, so that the electric current
flows from one of the bars C, to the bar D, and from this to the other bar C, and in
this manner we obtain a very delicate but continuous contact between the electrodes,
the weighted end of the bar D, preventing it from being thrown out of contact by any
sound vibrations no matter of what character.
These bars or electrodes are made of the best hard carbon (we prefer what is known
as Carri's carbon) and have their surfaces highly polished so that they present to each
other a great number of very fine points of contact, and as the vibrations of the dia-
phragm, under the influence of sound waves, are imparted to them, there is a very
delicate variation of each and all of these fine contacts and the electric current is
therefore varied to a great degree.
In to properly protect the carbon bars from extraneous substances that might
interfere with their operation or their high condition of polish we provide a cover E,
which may be of paper or the like and which we secure to the sides of the bridge
piece by gum and which extends over the electrodes as seen in the drawing (Fig. 3).
Instead of using three electrodes a greater number may be used when desirable, and
in Fig. 5 we have shown one modified form in which the carbons C, C1, C2, C³, are
secured to the bridge piece and the carbons D, D2, and 13 rest upon them. In this
case one end of the line wire may be connected to the carbons C, and the other to the
carbons D, so that the current passes through them in multiple arc.
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 :—
1. The combination with the diaphragm, of the bridge piece secured thereto, the
bars secured to the bridge piece and connected to the line, and the suspended and
weighted bar resting on and between said bars, substantially as described.
2. The combination with the diaphragm and the bridge picce carrying the carbon
bars, of a covering connected to the bridge piece and extending over the bars, sub-
stantially as described.
3. The combination with the diaphragm, of the bridge piece (the elevated end of
which bears upon the centre of the diaphragm while the other is secured at or near the
edge) of the carbon bars carried by the bridge piece, and of the weighted bar resting
upon and between the fixed bars, substantially as described.
PHILIP M. JUSTICE,
55 & 56 Chancery Lane, London,
Agent for the Applicants.