Neumann MM 2, MM 5, MM 3 User Manual

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the microphone company

Calibration Microphones
MM 2, MM 3, MM 5

As an audio pioneer, Neumann
is constantly charting new terri­tory. In the early years, when
microphone production was still
in its infancy, new problems
were encountered at nearly eve­ry turn. For example, how can a
thin diaphragm be produced
from plastic? Neumann solved
this particular problem by heat­ing the plastic and pouring a con­trolled amount onto the surface
of water.

For the very first microphone
amplifiers, resistors were fash­ioned from thin bars of graphite.
Acoustic measuring devices
hardly existed. So Neumann de­veloped the first practical loga­rithmic level recorder. For the
absolute calibration of pressure
microphones, Neumann de­signed a pistonphone. In the best
pioneering tradition, Neumann
used these devices as indispen­sable tools and aids for explor­ing the frontiers of acoustic re­search and the realization of in­novative ideas.

The industry also lacked a cali­bration standard for the acous­tic testing of microphones. In
1949 Neumann developed a
miniature microphone capsule
that functioned as a pressure
transducer. The aluminum mem­brane measures 10 mm in diam­eter. To prevent disturbing the
sound field in the calibration
room by the relatively large mi­crophone amplifier, the capsule
assembly is separated from the
amplifier housing with electri­cal 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 qual­ity control of its own microphone production. The combi­nation of the calibration microphone with one level record­er served to maintain a
constant sound pressure
level in the calibration
room, independent of the
frequency. The second lev­el recorder monitored the
output voltage of the mi­crophone under investiga­tion.

The MM 2 was succeeded
in 1954 by the MM 3,
which had the same speci­fications, but was equipped
with the AC 701(k) tube
in place of the VF 14 M.

For detecting higher fre­quencies 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 tol­erance is less than 3 dB.
These close tolerances
were regularly checked in
cooperation with the Nat­ural Metrology Institute in
Braunschweig, (now Phy­sikalisch Technische Bun­desanstalt, the German
equivalent of National Bu­reau of Standards).

Just as Neumann level
recorders were standard
equipment in most acous­tic calibration laboratories
of the time, Neumann
calibration microphones
served for decades as the
standard for nearly all
manufacturers of microphones and loudspeakers. Calibra­tion microphones continued to be produced until the ear­ly 1970s. Today, almost thirty years later, many of them
are still in service.