3-01This specification covers 2 \(two\) hand-held Dynamic Microphones, with or without a self-contained transistor amplifier and different connectors for use in unique military equipment. A wall-mounted holder is also included.

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MIL-DTL-21393B

3.5.1.2 Contents of the unit. The microphones shall be composed of the following:

a. Microphone back assembly, including the push-button, switch, cordage and plug,

as illustrated in the specification sheet (see 3.1).

b. Transmitter assembly, including the microphone element, with or without the

microphone amplifier (see 3.1). The element and the amplifier shall be designed to be

compatible, with each other.

3.5.2 Cordage (see 4.6.3.1.1). The cordage shall be retractile, shall have four unshielded (M21393/1-

01) or shielded (M21393/2-01) stranded wire conductors (see 3.1) and conform to type I of

MIL-DTL-55668 or an equivalent, which shall be approved by the procuring activity.

3.5.2.1 Anchorage (see 4.6.3.1.2). The cordage, all connections, and associated hardware shall show

no signs of reduced diameter, deformation, breakage, or loosened connection(s) at the microphone and

connector, following the anchorage tension test.

3.5.2.2 Connector. One end of the cordage shall be equipped with a plug, type PJ-068 in accordance

with MIL-DTL-642/5 (M21393/1-01) or U-229 in accordance with MIL-DTL-55116/1 (M21393/2-01)

3.5.3 Switch action. The switch shall be of the plunger type having an axial movement of

approximately 1/8 inch. It shall be designed for operation by a heavily gloved hand. The pressure

required to depress the switch fully shall not exceed 4 pounds. A pressure of at least 1.5 pounds shall be

required to hold the switch closed. The switch shall not have a detent action. For the M21393/1-01, the

closing of the audio and the control contacts shall occur very near simultaneously. The switch shall be

capable of at least 100,000 operations without mechanical or electrical failure.

3.5.4 Holder, microphone M21393/3-01. The microphone holder shall conform to the dimensions in

accordance with MIL-DTL-21393/3 and shall be suitable for permanent installation. It shall be designed

so that the microphone can be quickly and easily stowed or removed by one hand. It shall hold the

microphone securely regardless of position. Its weight shall not exceed 1.5 ounces (see 3.1).

3.6 Performance requirements.

3.6.1 Sensitivity (see 4.6.3.2.1). The audio output of the microphone, when measured as specified in

3.6.2 at a sound pressure level of 115 dB above 20 micro-Pascal (�Pa) and at a frequency of 1000 Hz,

shall be 54 � 3 dB above 1 millivolt. The sensitivity of the microphone shall not vary by more than 3 dB

after being subjected to any, or all, of the service conditions specified herein. At a simulated altitude of

10,000 feet, the sensitivity shall not fall below the sensitivity at sea level by more than 3 dB.

3.6.2 Frequency response (see 4.6.3.2.2). The frequency response of the microphone, when

measured as specified in 4.6.3.2 and compared to the response of 54 � 3 dB at 1000 Hz, shall be within

the limits shown in figure 5. However, the difference between any two successive readings, 100 Hz apart

up to 1000 Hz or 250 Hz apart above 1000 Hz, shall not exceed 2.5 dB, under all standard and service

conditions.

3.6.3 Linearity (see 4.6.3.2.3). The output voltage of the microphone shall be a linear function within

10%, of the input sound pressure in the range of 80 dB to 125 dB above 20 �Pa.