Improvements in Microphones.
Year: 1889

page_text: Improvements in Microphones.
A communication from EDUARD HEYDLER, of Hechtstrasse, 7, Dresden, in the Empire.
of Germany, Mechanical Engineer.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,.
M.I.M.E., 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 :-
The present invention relates to a so-called double microphone which is provided
with two microphone elements. All parts appertaining thereto are fixed to the plates.
which form the diaphragm. The carbon discs are secured rigidly to these plates and
the carbon points which are in contact with the said discs are attached elastically
thereto.
In view of the well-known facts that carbon alters its electrical resistance with
the force of the pressure which is exerted upon it and that in an inverse ratio.
of proportion, and that the intensity of an electrical current in a circuit in which
a circuit-breaker is included alters in proportion with the pressure exerted on the
contact points of the conducting parts of the circuit-breakers, two microphone
elements are employed in the present invention and these are arranged in such a
manner that the three carbon points of each bear with a light pressure against the
carbon discs in consequence of the elastic support. In consequence of the light
pressure of the points of contact and the light pressure on the carbon discs such
an element offers a very great resistance to the electrical current.
As soon however as the pressure is increased by the vibrating movement of the
diaphragm during the speaking the resistance is decreased materially and the
intensity of the current will be increased in proportion. If the battery current is
then passed consecutively through two such elements these variations will be greater
still and as in each element three carbon points are in contact with the carbon
disc a great resistance is offered with a light pressure and a very small resistance
with an increased pressure, the variations in the intensity of the current will be much.
greater than if only one contact was employed.

page_text: Fig. 1 represents a front elevation of the microphone,
Fig. 2 a side elevation and
Fig. 3 a plan of the same.
To the wooden disc a serving as the diaphragm are screwed the carbon discs bb'
which are electrically connected by a metal strip c. Above each of these carbon
discs three carbon points d d¹ are supported in sockets e e¹ fixed to the plates ff.
Each of these plates ff is fastened to an india-rubber strip k or k¹ by means of the
clamping plate g or g₁ with the screw threaded pins / or ', and the nuts i or i¹. The
ends of the india-rubber strips are held in clamps of the plates m m' which latter
are adjustably supported on the standards n n' by means of adjustable nuts o o'. These
standards are fixed in the diaphragm a.
The battery current is passed first through one of the plates for f1 to the carbon
points or d³, from there it passes through one of the carbon discs bor b' and through
the metal strip c to the other carbon disc and thence through the carbon points d or d¹
of that disc and the plate for f' to the line wire. By means of the nuts i i¹ and oo¹
the pressure of the carbon points d d¹ on the carbon discs & b¹ can be adjusted to a
nicety.
In consequence of the standards n n¹ being fixed to the diaphragm a all parts of
the microphone must participate the vibrations of the diaphragm during the
speaking. This arrangement effectually prevents any circuit breaking which in
microphones of other construction causes the jarring and crackling sounds.
The carbon points being supported clastically they will always remain in contact
with their carbon discs, when a percussion is exerted on the diaphragm and in
consequence of this arrangement all sound waves coming from any other source but
the diaphragm will have no effect on the microphone.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is ;-
1. In a microphone the arrangement of two electrically connected carbon discs
such as bon a diaphragm a in combination with a contact piece consisting
essentially of three carbon points for each disc through which points the current
passes so that it goes first through the carbon points of one side to the respective
carbon disc and from this to the carbon disc of the other side and thence through the
respective carbon points substantially as herein described and illustrated in the
accompanying drawings.
2. In an arrangement such as described in the foregoing clause the elastic support
of the plates ff carrying the carbon points and the arrangement of standards such
as n n carrying the elastic supports on the diaphragm for the purpose of preventing
any breaking of contact between the carbon points and the carbon discs and to render
all sound waves not coming from the diaphragm ineffectual substantially as herein
described and illustrated in the accompanying drawings.
Dated this 24th day of April 1889