Description and Applications The Model 644 is a highly directional dynamic microphone utilizing a combination of cardioid and distributed front opening designs. This gives greatly extended frontal pickup on the microphone axis, extending working distance over 2.5 times compared to present non-directional type microphones. Above 700 cps cancellation of sound at the rear and sides exceeds 20 dB providing unequalled rejection of random noise, reverberation and feedback without sacrifice of frequency response. The Model 644 allows much greater latitude in loudspeaker placement and will solve many specialized problems where mics cannot be placed near the source of sound.
A front acceptance angle at high frequencies of 45° each side of the microphone axis also allows best isolation of individual performers when desired. The Model 644 gives improved wind noise rejection compared with conventional microphones and is much less susceptible to generation of noise from mechanical shock.
Frequency Response: 40 to 12,000 cps. See Figure 1
Directional Characteristics: Cardioid to 700 cycles, 20 to 25 dB of rejection at the sides and rear above 700 cycles. See Figure 2
On-Off Switch: Sliding contact shorts microphone in “Off” position
Impedance: 150 ohms or High Impedance
Impedance Selection: Selection is made at cable connector. To change from High to 150-ohm impedance, move white lead from Terminal 2 to Terminal 3 on MC4M connector. 150 ohm impedance is balanced to ground
Output Level: High Impedance: –53 dB; EIA sensitivity rating: –149 dB 150-ohm Impedance: –53 dB; EIA sensitivity rating: –147 dB
Diaphragm: Electro-Voice Acoustalloy®
Case: Pressure-cast zinc and brass
Finish: Satin Chrome or Fawn Beige
Dimensions: Maximum diameter 25⁄16". See Figure 3
Net Weight: 2 pounds, 9 ounces, less cable
Cable Connector: Amphenol MC4M
Text and illustrations are from Electro-Voice Engineering Data, 644 Sound Spot Microphone, Part No. 533608, January, 1967.