neumann.berlin
the microphone company
U 47 –The Legend
For approximately 20 years Neumann had manufactured
and sold throughout the world the condenser microphone
CMV 3, also known as the “Neumann-Bottle”. Building on
its success it became time to start something new.
The cardioid M 7 microphone capsule had been manufac-
tured for many years with two equal diaphragms fixed on
both sides of a perforated center electrode which is also
provided with a number
of cavities on both sides
.One of the membranes is
gold coated and thus elec-
trically active. This mem-
brane is directed towards
the sound source.
The sound coming from
the front causes move-
ment of the front mem-
brane and reaches the in-
ner side of the rear mem-
brane
through
the
perforations in the electrode. The sound also reaches the
outside of the rear membrane. The acoustic properties
of the center electrode cause the forces acting on the rear
membrane to be equal in size, but opposite in direction.
Therefor, the rear membrane does not move and does not
produce any electrical signal. For sound arriving from be-
hind, the rear membrane moves and the front membrane
does not. As a consequence, the microphone does not re-
spond to rear sound, and
the directional character-
istic is cardioid.
Both capsule halves thus
act as a cardioid capsule
and led Neumann to
make the rear membrane
electrically active by coat-
ing it with gold too.
When connecting both
cardioid halves in parallel,
the capsule produces an
omni directional pattern.
If only one membrane is
connected, the microphone works as described above as a
cardioid.
which may be partially responsible for its legendary lon-
gevity by providing a low humidity environment for the
capsule. This was certainly not responsible for the “full,
rich and warm sound” the U 47 is famous for, a sound qual-
ity still highly regarded in our days. Many recording studi-
os are proud to claim ownership of a working U 47.
During the 1950’s Neumann microphones also were sold
through Telefunken, and carried the Telefunken logo. Thus
the U 47 was also known as the “Telly”. It was reported
about “The Voice”, Frank Sinatra, that he wouldn’t sing
without his “Telly”, the Neumann U 47. From the Bar-
clay Studios in Paris, which were technically supervised
by Gerhard Lehner, we learned of people admiringly claim-
ing: That’s a microphone to drive nails into walls with.
Whether this is understood literally or figuratively, it is a
compliment for the U 47 either way!
The prerequisites for an easily switchable microphone with
two directional characteristics were now fulfilled. A steel
vacuum tube VF 14 M was selected for the impedance
converter/amplifier, a pentode being operated as triode.
The microphone was fed with one supply voltage only, from
which the filament voltage was derived by means of a wire
wound resistor inside the amplifier housing. Consequently
the microphone itself produced a fair amount of heat,
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