The Altec Lansing Model 684A omnidirectional dynamic microphone
This microphone is the nearest approximation to the laboratory quality of the famous Altec 21D condenser type. Developed to meet the requirements for a professional dynamic microphone, the Altec Model 684A has an omni-directional polar pattern in character with wide uniform frequency response from 35 to 20,000 cycles.
The rugged moving coil design assures long life and uninterrupted operation. The Altec “Golden” diaphragm and pressure element is further protected by the famous Altec sintered bronze filter against contamination of moisture, dirt, dust and foreign particles.
The Model 684A is conical in shape and finished in non-glare TV dark green and black, preventing unwanted light reﬂections when on camera, or distractions to recording artists. It is comfortably balanced for hand-held use, such as interview shows, or may be used with “Slip-On” Adapter No. 13798 for attaching the microphone to any ⅝" × 27 thread microphone stand. The microphone is supplied with fifteen feet of two conductor, shielded microphone cable.
Before placing the microphone into service, determine the impedance requirements of the input system into which the microphone will connect, then by following the procedure outlined in Figure 1, select the proper connections.
A calibration curve on this microphone will be found on the inside cover of the storage case. It provides an accurate performance record of the microphone. This calibration is made in the Altec anechoic chamber equipped with an accurately controlled transducer as a sound source. The performance is recorded on Altec measuring equipment by an automatic servo-driven charting pen. The Altec calibration standards are cross-checked at regular intervals by independent acoustical laboratories.
Type: Moving Coil Dynamic
Pickup Pattern: Omni-directional
Frequency Response: 35 to 20,000 cycles
Output Impedance: 30/50, 150/250 and 20,000 ohms (selection by connections in microphone cable plug)
Output Level: –55 dBm/10 dynes/cm2
Hum: –120 dB (ref: 103 Gauss)
Dimensions: 1⅛" diameter at top (1½" largest diameter) 7½" long not including plug
Weight: 8 ozs. (not including cable and plug)
Finish: Two-tone baked enamel, black and dark green
Mounting: Separate “Slip-On” Adapter No. 13798 furnished. Adapter has standard ⅝" × 27 thread. (Calibration Chart included with each 684A)