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Sennheiser Stasi
Buttonhole microphone
MM-23
is a miniature microphone, also known as
buttonhole microphone or lapel microphone,
developed and manufactured from the mid-1960s
onwards by
Sennheiser Electronic Laboratories
in Wennebostel (Germany).
During the Cold War
it was one of the favorite 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 a coaxial socket for connection of the audio cable at the bottom,
and a button-type sound port at the front, allowing it to be worn in clear
view through the buttonhole of a jacket. The complete microphone weighs
just 4 grams and has an excellent frequency response, that covers the
400 - 4000 Hz voice spectrum.
Like the Sennsheiser
MM-61 Concealed Fountain Pen microphone,
the MM-23 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 covertly making
recordings and transmissions. As it was worn overtly
(i.e. not concealed) it delivers a far better audio quality than a
concealed one, which is often hidden under the operative's clothing.
The MM-23 was first sold in 1964, and was available for no more than DM 43. 1
It was in production until the mid-1970s.
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List price in 1964: DM 43 (approx. EUR 22).
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Type Dynamic Frequency 400 - 4000 Hz ±3dB Impedance 2000Ω Sensitivity 0.12 mV/µbar @ 1000 Hz with 2kΩ load Connection Standard electronic flash light socket Size 18.9 x 15.5 x 12.6 mm Weight 4 grams Material Metal Shape Rectangular with button-type sound port First sold 1964 Last sold 1975
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© Crypto Museum. Created: Wednesday 05 April 2017. Last changed: Wednesday, 05 November 2025 - 11:43 CET.
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