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Covert microphone capsules
Sennheiser is a German privately held manufacturer of professional audio
equipment, specialising in the development and production of a wide range
of high-end
products, such as (wireless) microphones, headphones, telephony accessories,
avionics headsets, conference equipment and other professional and
business applications. It has its headquarters in Wedemark (Germany).
Over the years, Sennheiser produced a wide range of
(bare) microphone elements,
that were used in products from other manufactuers (OEM).
During the Cold War,
such microphones were used in
covert listening devices (bugs)
and covert recording equipment,
by both sides of the Iron Curtain.
➤ More about Sennheiser
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Sennheiser microphones on this website
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The MM-23 was available in a number variants, each haused in a similar
enclosure, but with a different sound port. Below are the Sennheiser capsules
that we have identified so far.
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This is the basic design of the MM-20 range. It consists of a rectangular
metal enclosure with curved edges, and is available in different versions,
each with a different sound port and an different frequency response curve,
adapted for a variety of applications.
The MM-21 has a small pin-hole sound port at the top surface.
At present, no image of an MM-21 is available, but it is very similar
to the MM-26, albeit with a smaller sound port.
➤ More information
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This is basically the same microphone, but with a slotted sound port at
one of the short sides.
The MM-22 shown here as seen quite some action and shows sign of corrosion.
It was used for many years by the US
Central Intelligence Agency (CIA)
with an SRT-56 bug.
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This is a special variant of the MM-20 range and was known as button
or lapel microphone. It has a rather special sound port at the top
surface that can be fitted through a buttonhole.
Unlike the other MM-20 variants, it does not have solder terminals. Instead
is has a socket to which a standard electronic flash light plug can be fitted.
Suitable plugs and cables were widely available at the time.
➤ More information
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This is the same capsule as the MM-21, but with a larger sound port at
the top surface. As a result, it has a better frequency response curve.
The one shown here is glued onto a metal bracket that was probably used
to attach it to the operator's clothing. It was found with a
Tesla E-120 Mini Corder
and shows that during the Cold War, the Western Sennheiser
microphones were also popular behind the Iron Curtain.
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MM-61 is a dynamic microphone disguised as a fountain pen.
Although officially announced for use in combination with dictation
machines, it is clear that it was much more suitable for covert
recording of conversations.
Despite its 'modern' look, the design is rather old. The MM-61
was manufactured from 1962 to 1975 and was used by both West and East.
➤ More information
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This microphone capsule was introduced around 1970 and occupies about
1/7 of the space of the other MM capsules, making it even more suitable
for use with covert listening devices (bugs).
Although it was originally intended for use with hearing aids, it soon
became the preferred microphone for bugs, not just in the West, but also
in Eastern Block countries like East Germany (DDR) and Czechoslovakia.
➤ More information
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© Crypto Museum. Created: Tuesday 19 June 2018. Last changed: Sunday, 04 December 2022 - 14:44 CET.
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