neumann.berlin
the microphone company
As an audio pioneer, Neumann
is constantly charting new terri-
tory. In the early years, when
microphone production was still
in its infancy, new problems
were encountered at nearly eve-
ry turn. For example, how can a
thin diaphragm be produced
from plastic? Neumann solved
this particular problem by heat-
ing the plastic and pouring a con-
trolled amount onto the surface
of water.
For the very first microphone
amplifiers, resistors were fash-
ioned from thin bars of graphite.
Acoustic measuring devices
hardly existed. So Neumann de-
veloped the first practical loga-
rithmic level recorder. For the
absolute calibration of pressure
microphones, Neumann de-
signed a pistonphone. In the best
pioneering tradition, Neumann
used these devices as indispen-
sable tools and aids for explor-
ing the frontiers of acoustic re-
search and the realization of in-
novative ideas.
The industry also lacked a cali-
bration standard for the acous-
tic testing of microphones. In
1949 Neumann developed a
miniature microphone capsule
that functioned as a pressure
transducer. The aluminum mem-
brane measures 10 mm in diam-
eter. To prevent disturbing the
sound field in the calibration
room by the relatively large mi-
crophone amplifier, the capsule
assembly is separated from the
amplifier housing with electri-
cal connection running through
a thin tube of 25 cm length. The
amplifier is modified from the
electronics used in the U 47,
with the same tube model
VF 14 M.
The calibration microphone features a linear frequency
range of 20-16,000 Hz, with a maximum deviation of
+/- 1 dB. Neumann used the calibration microphone in
conjunction with two Neumann P2 level recorders for qual-
ity control of its own microphone production. The combi-
nation of the calibration microphone with one level record-
er served to maintain a
constant sound pressure
level in the calibration
room, independent of the
frequency. The second lev-
el recorder monitored the
output voltage of the mi-
crophone under investiga-
tion.
The MM 2 was succeeded
in 1954 by the MM 3,
which had the same speci-
fications, but was equipped
with the AC 701(k) tube
in place of the VF 14 M.
For detecting higher fre-
quencies up to 50 kHz –
for example, when testing
acoustic models in reduced scale – Neumann developed
an even smaller capsule with a Nickel diaphragm, known
as the MM 5. Introduced in 1955, the MM 5’s frequency
response up to 20 kHz is as consistent as that of the MM 2
and MM 3. In the 20 kHz
to 50 kHz range, the tol-
erance is less than 3 dB.
These close tolerances
were regularly checked in
cooperation with the Nat-
ural Metrology Institute in
Braunschweig, (now Phy-
sikalisch Technische Bun-
desanstalt, the German
equivalent of National Bu-
reau of Standards).
Just as Neumann level
recorders were standard
equipment in most acous-
tic calibration laboratories
of the time, Neumann
calibration microphones
served for decades as the
standard for nearly all
manufacturers of microphones and loudspeakers. Calibra-
tion microphones continued to be produced until the ear-
ly 1970s. Today, almost thirty years later, many of them
are still in service.
Calibration Microphones
MM 2, MM 3, MM 5
