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The RCA Type 77-B1
Unidirectional Microphone

The RCA Type 77-B1

Hear the sound of this mic voiced by Ellis Dawson.

The Type 77-B1 Unidirectional Microphone can be used to excellent advantage in practically any type of studio installation. For example, in an auditorium this Unidirectional microphone call be used to pick up the entire action on the stage because of its cardioid pattern and will suppress, approximately 20 to 1, any undesirable noises originating in the audience. It can also be used to advantage in small studios where the reverberation time tends to be objectionable, precluding the use of a non-directional microphone. In a given studio, the Type 77-B1 micro­phone can he used with approximately 1.73 times the reverber­ation pickup than a non-directional microphone. It is ideal for applications where it is necessary to place a microphone close to a wall or window, since the pickup of reflected sound from the wall or glass is reduced.

The RCA Type 77-B1

Its operation is similar to that of the type 77-A Unidirectional micro­phone which it supersedes, namely a single ribbon fixed at the center, one half operating as a velocity microphone and the other half oper­ating as a pressure type. The two outputs of the ribbon are connected in series and the resultant vector addition of the generated voltage pro­duces a directional characteristic as shown below. This curve also shows the uniformity of the directional response with respect to frequency. The small size, light weight, rugged construc­tion and good sensitivity of the 77-B1 recommend it as one which no station can afford to lack.

Polar pattern


  • Output Impedances: 50/250/500 Ohms

  • Output Level: −66 VU
    Sound pressure: 10 dynes per centimeter squared
    with output terminated into a matched load

  • Frequency Response: See curve

  • Directional Ratio: 10 to 1 −20 dB

  • Finish: Polished Black and Chromium

  • Mounting: ½-inch pipe thread

  • Dimensions: Overall length (including mounting) 10 inches;
    width 3¾ inches; depth 2½ inches

  • Weight: Unpacked including mounting 2 pounds

Frequency reponse

The RCA Type 77-B1

The RCA Type 77-B1
Above photographs and sound sample are via the courtesy of Ellis Dawson.

Chrome-bottomed RCA Type 77-B1
A unique chrome cup on a 77-B1.

The RCA Type 77-B1
Unidirectional Microphone
MI-2199, U.S. Army issue

U.S. Army Type 77-B1

U.S. Army Type 77-B1

U.S. Army Type 77-B1

U.S. Army Type 77-B1
The U.S. Army version of the Type 77-B1.
Photos are via the courtesy of Dennis Schrank.

RCA Type 77-B1
Download the data sheet for this mic.


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