Microphone with a narrow polar pattern. Scheme, description

Microphone with a narrow polar pattern. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Audio equipment

A narrow-beam microphone can be used when recording and amplifying speech in conditions of high noise, as well as recording sounds from distant sources, such as birdsong. The directivity of the microphone significantly increases the signal-to-noise ratio at the input of the bass amplifier.

Schematically, the device of such a microphone is shown in Fig.1. Its main detail is an electromagnetic primer (3) placed in a cylindrical case (1). The capsule is filled with epoxy resin on both sides. The side of the capsule facing the open opening of the case has a small "sensing window" that provides sound vibrations with access to the membrane. With the help of three stretch marks, the capsule is suspended on a wire ring (4), which is located in the back of the case. To reduce reflection from the walls, the inside of the case is covered with a layer of felt or felt (2) about 12 mm thick.

The microphone is connected to the input of the preamplifier, one of the possible circuits of which is shown in fig. 2. Reducing the inherent noise of the first stage is achieved by choosing a low-noise transistor T1 and using it at low collector current. The second stage, assembled on a transistor T2 according to a common collector circuit, allows you to match the output of the device with a power amplifier.

Narrow-beam microphone
Preamp circuit

A DEMSH capsule can be used as a microphone capsule. For the first stage, you can take the transistor MP111A, for the second - MP38A.

Publication: N. Bolshakov, rf.atnn.ru

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