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Audium T-7114
Covert microphone

T-7114 and T-7314, were subminiature microphones, made in the early 1960s, by hearing aid manufacturer Audium in Amsterdam (Netherlands). Although originally intended and used for hearing aids, they were used for a number of years by the US Central Intelligence Agency (CIA) in combination with the Easy Chair listening devices developed by the Dutch Radar Laboratory (NRP).
 
According to the datasheet [A], the microphone covers the voice spectrum, and performs best between 600 and 5000 Hz, with a preference for the higher frequecies. Measuring just 9.7 x 9.7 x 5 mm and weighting less than one gram, it was one of the smallest microphones of its time.

The image on the right shows the 7114, which has a soft optional sound port that allows the microphone to be housed inside a concealment. By extending the sound port with a hollow pipe or flexible tube, it can also be used as a probe microphone, much like the CIA's larger Type-B.
  
Audium T-7114 subminiature microphone (1962)

Because of its small dimensions, the T-7114 was used for a number of years in combination with Easy Chair Mark V listening devices, as an alternative for the (better but larger) Shure MC-30. Both microphones were eventually superceeded by the Knowles BA-1501 and the BA-1502.
 
Audium T-7114 subminiature microphone (1962)

 
Comparision
The image below shows the Audium T-7114 in comparison with other microphones of the era. The T-7114 is visible at the bottom right (with the two yellow wires). At the bottom left is the Shure MC-30. At the front centre are the later Knowles BA-1501 and BA-1502.

A collection of microphones that were used with Easy Chair equipment.


 
Specifications
  • Frequency
    600 - 4000 Hz
  • Impedance
    2500Ω at 1000 Hz
  • Size
    9.7 x 9.7 x 5 mm
  • Weight
    < 1 gram
  • Material
    Metal
  • Connection
    Solder pads
Documentation
  1. T-7114 and T-7314 datasheet
    Audium. 6 September 1962.

Further information

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Crypto Museum. Created: Wednesday 05 April 2017. Last changed: Wednesday, 05 April 2017 - 13:12 CET.
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