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Covert microphone

DD-4 was a dynamic low-impedance microphone, developed in the mid-1950s by the American Microphone Company (AMC). It was used by the US Central Intelligence Agency (CIA) for (wired) room overhearing and recording, as well as in combination with wireless covert listening devices.

The device has a diameter of 41 mm and is 23 mm thick, which was considered very small at the time. It was first publicly disclosed in 1957 in the article Secrets of the Electronic Snoopers in the October issue of Popular Science [2]. In the article, several examples of the wired use of the device are given. Due to its low-impedance nature, it can be connected to a recording device several hundred metres away without picking up hum or noise from nearby electricity cables [2].

The DD-4 is also mentioned in the book Spycraft by H. Keith Melton and Robert Wallace [3 p. 46].
DD-4 microphone used with CIA bugs

In the Autumn of 1955, a technician working for the DCI security detail, installed several covert microphones in the newly built suite for the Director of Central Intelligence (DCI) in Washington. They were wired directly to a recording room elsewhere in the building. One of the microphones was hidden behind the ceiling right above the DCI's desk. it was rediscovered 15 years later, in 1970, after the CIA had abandonned the building and moved to Langley. The building was then assigned to the CIAs Technical Services Division (TSD). When a technician removed one of the acoustic tiles in the ceiling, he found the DD-4 hanging by its (now unconnected) wires [3 p.487].

Another example of the use of DD-4 microphones in the mid 1950s, is during the CIA's research program MKULTRA 1 — a secret mind-control and interrogation research program run by the Office of Scientific Intelligence (OSI) [4]. As part of the sub-project Operation Midnight Climax, the CIA established a brothel 2 in the San Fransisco bay area to covertly test the effect of drugs — in particular LSD — on the behaviour of unwitting visitors of all social backgrounds [5]. Hired technician Bill Hawkins, at the time a 24 year old student at UC Berkeley, installed several DD-4 microphones behind false wall sockets and two-way mirrors. They were used for recording [6][7].

  1. Also written as MK/ULTRA, MK-Ultra and MKUltra.
  2. A rented appartment at 225C Chestnut Street in Los Angeles.

DD-4 microphone used with CIA bugs
DD-4 microphone compared to a Shure MC-11G
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DD-4 microphone used with CIA bugs
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DD-4 microphone compared to a Shure MC-11G

  1. Pete McCollum, DD-4 microphone - THANKS !
    Received September 2020.

  2. Wesley S. Griswold, Secrets of the Electronic Snoopers
    Popular Science. October 1957, pp. 126-130 & 238.

  3. Robert Wallace & H. Keith Melton, Spycraft
    ISBN 978-0-452-29547-6.

  4. Wikipedia, MKUltra
    Visited 27 August 2023.

  5. Wikipedia, Operations Midnight Climax
    Visited 27 August 2023.

  6. John Marks, The Search for the 'Manchurian Candidate' - The CIA and Mind Control 1
    ISBN 07139-12790. 1997. pp. 93-94.

  7. Uncovering The Undercover Men Behind Bay Brothel
    Berkeley Harb, 26 August - 1 September 1977. p. 3.
  1. Not to be confused with Richard Condon's 1959 novel The Manchurian Candidate, that was adapted into a feature film twice: in 1962 and in 2004.

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Crypto Museum. Created: Sunday 27 August 2023. Last changed: Monday, 28 August 2023 - 05:44 CET.
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