Improvements in Microphones.
Year: 1898

page_text: Date of Application, 18th Mar., 1898-Accepted, 30th Apr., 1898
Improvements in Microphones.
I, LARS MAGNUS ERICSSON, of Thulegatan 5, Stockholm, in the Kingdom of
Sweden, Manufacturer, 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 microphones containing granular carbon, the object
being to provide means for retaining the granular material in position and for damp-
ing the vibrations of the diaphragm.
an
One of the principal difficulties encountered in attempting to provide a good
carbon microphone containing granular carbon has been the devising of an arrange-
ment for retaining the granular material securely in place without exerting an
undue and varying pressure on the diaphragm. This invention relates to
arrangement by means of which this difficulty is overcome, the said arrangement
consisting in enclosing the mass of granular carbon in an elastic material which is
made to exert a uniform (not a varying) pressure on the diaphragm whilst at the
same time taking part in its vibrations and thus damping the latter to a certain
extent,
In the accompanying drawing,
Figure 1 is a vertical section of a microphone constructed according to the inven-
tion:
Figure 2 is a plan view thereof; and
Figures 3, 4, 5 and 6 are views of details.
The microphone consists of a cylindrical carbon disc K (Figure 3) having in the
portion that faces the diaphragm k, cavities c (here shewn seven in number) in which
(as usual) are placed small cylinders made of felt, cloth or other suitable elastic
The carbon disc K is
material for keeping the granular carbon in a loose condition.
fastened to the metal casing of the microphone by means of the screw u passing
through the central cavity c. Around the said carbon disc K there is arranged a
ring R of felt, cloth or other suitable elastic material and this ring is pressed against
the carbon diaphragm k by means of the spring-plate f (Figures 1 and 4), or by spiral
or leaf-springs (Figures 5 and 6). In lieu of springs of one kind or another a hollow
ring of rubber, gutta-percha or other similar material may be used. The space
bounded by the carbon disc K, carbon diaphragm k and felt ring R is filled with a
suitable quantity of granulated carbon g. The elastic, spring-ring R thus serves
both to retain the granulated carbon in its place and to exert an even, constant
pressure on the diaphragm during its vibrations. By this arrangement a good
articulation is obtained and at the same time the sound will not be disagreeable to
the ear even when the voice of the person speaking is loud or strident.
In order to protect the interior parts of the microphone from dampness and dust,
a waterproof membrane S of impregnated silk or other suitable material is located in
front of the carbon diaphragm k.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what I
claim is:
1. In microphones containing granular carbon, the described arrangement con-
sisting of a ring of felt, cloth or other suitable elastic material which is pressed by
a suitable spring-device (for instance, a spring-plate, spiral or leaf-springs, or a
hollow rubber ring) against the microphone-diaphragm with an even, constant
pressure, so as to retain the granular carbon in position and at the same time damp
the vibrations of the diaphragm, substantially as hereinbefore described.
2. The manufacture and use of the improved microphone hereinbefore described
and illustrated in the accompanying drawing.
T
101
1000
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.