Type: Hand-held, close-talking, omnidirectional dynamic microphone
Frequency Response: 180-10,000 Hz
Output Level: -60 d B m at 1 Pa
Impedance: 150/250f2
Pickup Pattern: Omnidirectional
Connections
Microphone: 2 shielded conductors Relay Control
Circuit: 2 unshielded conductors
Dimensions: 2'/z" (6.4 cm) W 35/a" (9.2 cm) L 2" (5.1 cm) H
Weight: 4.5 oz. (127.6 gm), less cable
Case: Impact-resistant plastic, charcoal gray
Cable: 51/2' extended, 10"-12" retracted 4-conductor (2 shielded, 2 unshielded) coil cord with neoprene jacket
Mounting Facility: Nickel-plated, spring steel, clip-type mounting bracket with two No. 6 sheet-metal screws 5/16" long
Operating Temperature Up to 180°F Range:

The omnidirectional dynamic microphone shall be the hand-held, close-talking type with a push-to-talk switch that shall enable simultaneous operation of relays, visual indicators, etc., with the muting of the audio circuit by means of an extra set of prewired contacts. The microphone shall be encased in an impact resistant housing with all internal components shock mounted for protection.
'10 dynes/cm2 = 1 Pascal= 10 Microbars

The microphone shall meet the following criteria: Frequency response from 100-5000 Hz. Sensitivity, -60 dBm/1 Pa. Impedance, 150/2500. Connections, 2 shielded conductors for audio circuit, 2 unshielded conductors for relay control circuit.

The microphone shall be the ALTEC LANSING Model D91 P.