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Mic Bugs CIA
Subminiature covert microphones
Knowles is a manufactuer of miniature microphones, based in Itasca (Illinois,
USA). The company was founded in 1946 by Hugo Knowles and was among the first
to manufacture subminiature microphones and speakers for hearing aids. In 1969,
NASA even took their microphones to the moon. Knowles microphones are also
found at the heart of many
covert listening devices (bugs).
Knowles microphones come in many flavours and sizes, ranging from the first
minature dynamic microphones that measured approx. 10 x 10 x 5 mm, to
state-of-the-art MEMS-based variants that measure no more than a couple of
millimetres.
During the Cold War,
much of the research and development at Knowles was financed by the
US Central Intelligence Agency (CIA),
who was one of their main customers.
The research was fed back to the CIA in a series of reports, e.g. [E].
Ironically, Knowles microphones were also used by the CIA's counterparts
in East-Europe, often under the pretence that they were needed for the
manufacture of hearing aids. A good example is the
31216 radio bug
of the repressive security service of the DDR (East-Germany) —
the Stasi.
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Knowles microphones on this website
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The Knowles 1501, also known as BA-1501, 1 was a very popular
dynamic element for military headsets as well as for the early generations
of covert listening devices (bugs)
used by the CIA.
It is also known as NSN 5965-00-015-7408.
In the 1960s and 1970s, the 1501 was used in a variety of bugs,
such as the SRT-107.
Measuring just 10 x 10 x 5 mm, the 1501 was one of the smallest
microphones at the time.
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The BA-1502 is basically identical to the BA-1501, except that
it has its sound port at one of its sides, rather than on the
top surface.
The image on the right shows the two variants side by side.
Depending on the application, the most suitable shape was used.
The two microphones shows here have been used in real life
bugging operations, in which they were covered in polyether
foam, that has clearly left its marks.
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Knowles also produced sub-miniature electret condenser microphones,
such as the BT-1750, BT-1751, etc. These microphones are
generally known as the BT-Series, and were also used during the Cold War
by the MfS (Stasi) of the former DDR (East-Germany) for use in their
listening devices (bugs).
➤ Download datasheet
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This microphone was developed especially for the CIA.
It was intended
for use in combination with covert equipment such as
covert agent radios
and covert listening devices (bugs).
It consists of a subminiature
Knowles electret microphone element that is cast in silicone.
The silicone body reduces any low-frequency vibrations caused by
conductance (e.g. through the walls of a building)
and makes it easier to handle the device.
➤ More information
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The letters 'BA' stand for Balanced Armature.
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Below is a non-exhaustive list of other types of Knowles devices
that have been reported [3]:
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- 1568
1582 Receiver (center-tapped) - 1588
1634 Receiver (center-tapped) 1681 Electret microphone 1687 Microphone with active pre-amplifier 1714 Dynamic microphone - 1722
- BT-1750
BT-1751 Electret microphone with sound port at the front BT-1959 Same but with large sound port at the top surface - 1784
- 19x43
1806 (dual port) BC-1520 (test?) TI 11214G Dynamic microphone
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Document kindly provided by Detlev Vreisleben [2].
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© Crypto Museum. Created: Sunday 29 January 2017. Last changed: Thursday, 14 November 2024 - 10:11 CET.
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