Carbon grain' microphones
Year: 1895

page_text: Date of Application, 18th Nov.,, 1895 Accepted, 14th Dec., 1895.
A. communication: by the Firm of; HAMMACHER, & PABTZOLD,, of 321 Andreas
Strasse, Berlin, in the Empire of Germany, Electricians..
I, WILLIAM PHILLIPS, THOMPSON, F.C.S., M.:M.E. of The Agency for
Foreign Patent Solicitors, 6 Lord, Street, Liverpool, and, 6 Bank Street,
Manchester, both in the County of Lancaster, 118 New Street, Birmingham
in the County of Warwick and 31 High Holborn in the County of Middlesex,
Civil Engineer, 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 :-
Carbon grain' microphones.ore telephone transmitters as; at present, constructed
have the drawback that carbon powder or dust, formed by mechanical wear, or by
combustion, cannot fall out of the instrument, but form current bridges at certain
points between the diaphragm and the back plate, where the edge of the diaphragm
does not extend owing to being clamped fast. At these points the current bridges
form side shunts with only very indifferent variation of resistance which is necessary
for transmitting sound in the microphone. The said drawback becomes particularly
apparent if the microphone be used in various positions. The carbon dust formed
falls back into different parts of the microphone, aud causes short circuiting and
side noises. Efforts have been made to remove these drawbacks by enclosing the
grains of carbon in cylindrical bodies of frieze or the like so that they actually rest
in front and behind against the current conveying parts of the microphone, and the
falling out of separated parts is entirely avoided. This arrangement has, however,
the drawback that the frieze body, or the like, acts with a damping effect ou the
vibrations of the diaphragm and therefore the sound conveyed is dulled and
weakened.
The present invention avoids the above mentioned drawbacks in that the carbon
grains are not wrapped and in that the released particles can fall freely out of the
instrument if the latter be placed in a vertical position, and also in that the carbon
dust can not again fall back into the microphone when its position is altered.
Further, by the present invention, the diaphragm may before the microphone is
placed in circuit be easily adjusted to the most susceptible position relative to the
carbon grains and to the back plate and even after considerable wear of the
microphone, said diaphragm may be easily readjusted.
The invention will now be described with reference to the accompanying drawings,
in which,
Figure 1 is a vertical section and
Figure 2 a plan.
The diaphragm m lies on a metal support r of annular form which is screwed to
the mouth-piece M of the microphone, and this diaphragm m is held fast by small
clamps f. A brass ring 6 is carried on feet i insulated from the annular support
and in said ring the back disc k is screwed, it being provided with a threads for
this purpose.
The back disc k is provided with recesses p to receive the carbon
grains. A spring contact a conveys the current from the back disc to the induction.
coil, and also prevents the disc from becoming loosened by accidental turning of the
screws after it has been adjusted to the best position for the most sensitive sound.
transmittance. The powder wearing off the carbon grains can, when the device is
.

page_text: placed in a vertical position fall between the feet which carry the back plate and
the brass ring, and is easily removed from the case of the microphone.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, as communicated to
me by my foreign correspondents, I declare that what I claim is :-
A microphone or telephone transmitter without any damping insertion between
the diaphragm (m) and the carbon diso (k) oharacterised by the conducting disc (k)
which has recesses:(p) to contain the carbon grains and which is arranged parallel
to the diaphragm (m) being held adjustably in a ring or socket (6), which is
supported by insulated feet (i) and connected with the annular support (r) of the
diaphragm (m), whereby the distance between the diaphragm (m) and the back
disc (k) may be regulated and whereby, the carbon dust produced may freely fall
out and be prevented from falling back onto the current conveying parts thereby
obviating any damping of the vibrations substantially as set forth.
10
WM. P. THOMPSON & Co.,
Agents.