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Sennheiser
Miniature microphone
- under construction
MM-21
is a miniature dynamic microphone,
developed and manufactured from the mid-1960s
onwards by
Sennheiser Electronic Laboratories
in Wennebostel (Germany), for use is small devices like hearing aids.
During the Cold War it was one of the favorite covert microphones of both
Western and Eastern intelligence and law enforcement agencies,
because of its high audio quality.
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The body of the microphone measures 19 x 12.6 x 6.7 mm.
It has two solder terminals at the long sides and a small circular sound port
at the front surface. The complete microphone weighs
just 4 grams and has a good frequency response that covers the
400 - 4000 Hz voice spectrum. It is the basic model of a series
with different types of sound port, like the
MM-23
and MM-26.
Like the Sennsheiser
MM-61 Concealed Fountain Pen microphone,
the MM-21 was initially meant for use in combination with dictation
machines and the first generations of (large) hearing aids.
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However, it was soon adopted as a concealed microphone for
covert listening devices (bugs), both in the west and behind the Iron Curtain.
The MM-21 was first sold in 1964, and was in production until the mid-1970s.
In 1971 it was available for a price of $ 9.90. 1
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Frequency 400 - 4000 Hz ±3dB Impedance 2000Ω Sensitivity 0.14 mV/µbar @ 1000 Hz with 2kΩ load Type Dynamic Connection Standard electronic flash light socket Size 18.9 x 15.5 x 12.6 mm Weight 5.4 grams Material Metal Shape Rectangular with circular sound port First sold 1964 Last sold 1975
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© Crypto Museum. Created: Tuesday 18 September 2018. Last changed: Wednesday, 05 November 2025 - 11:43 CET.
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