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The Altec Lansing Model 684A
omnidirectional dynamic microphone

The Altec 684A


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 58" x 27 thread micro­phone stand. The micro­phone is supplied with fifteen feet of two conductor, shielded micro­phone cable.

Impedance Selection
Before placing the micro­phone in 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.

Figure 1

Calibration Chart
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.

Frequency response


  • 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: 118" 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 58" x 27 thread. (Calibration Chart included with each 684A)

Text and illustrations are from Altec Lansing Corporation instructions 13524 copyright © 1961

Altec 684A
Microphone courtesy of Jeff Rudisill

Operating instructions
Download the Operating Instructions for this mic.

Altec 684B specification sheet
Download the specification sheet for the 684B.


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