The Electro-Voice Model 664A Dual-Z dynamic supercardioid microphone
Description and Applications The Electro-Voice Model 664A is a rugged dynamic supercardioid microphone designed to provide reliable service in the many situations in which directional microphones are required. Nearly all directional microphones exhibit proximity effect (a boost in low frequency response) when used near a sound source. The 664A does not, because it utilizes the Electro-Voice patented Variable-D principle. Therefore, the 664A will respond more accurately in those situations that demand the talker, singer, or instrument to be close to the microphone (see Figure 1).
The principle underlying “close miking” is that the sound pressure level at the microphone increases 6 dB each time the distance from the sound source is halved. Obviously the output level of the microphone then increases proportionately, resulting in a louder sound system or a better signal-to-noise ratio on a recording. “Close miking” can also reduce the often undesirable effects of reverberation as well as provide an increased separation among competing sounds.
As a supercardioid, the 664A provides maximum rejection at 150 degrees rather than the 180 degrees of a cardioid. This assures greatest rejection in the horizontal plane when the microphone is tilted in its most natural position, 30 degrees from the horizontal (as on a desk or floor stand). The polar response (sound source at varying angles to the microphone diaphragm) is exceptionally uniform with little or no off-axis coloration. This is important, because it means the microphone’s response in actual use will closely parallel the anechoic on-axis curve (see Figure 2). Many cardioids have good on-axis response, but radically different response at other angles, meaning the microphone’s published curve (undoubtedly on axis, anechoic) is of little practical use.
The 664A uses the mechanical nesting concept of design, providing a nearly solid mechanical structure that is highly resistant to damage from shock. The exclusive non-metallic Electro-Voice Acoustalloy diaphragm is virtually unaffected by extremes of atmospheric conditions. The case is made of pressure-cast zinc with chrome plating.
Impedance Change Instructions The 664A features a new impedance selector combined with the on/off switch. Either balanced 150 ohms or unbalanced Hi-Z output may be selected and locked with the flip of a switch and the turn of a screw. No wires to change, and the selected impedance is plainly indicated.
Look at the on/off switch located on the microphone stud (see Figure 3). Through the opening for the slider you will see either the word Hi or Lo indicating the present impedance. To change to the opposite impedance, remove the upper switch screw, the one nearer the microphone. Now push the switch button toward the indicated impedance (Hi or Lo). The switch button will slide the undesired impedance indication out of sight (push it all the way), and bring the desired impedance into view at the opposite end of the slot. Replace the switch screw and tighten. That’s all there is to it. The impedance has been switched to the condition indicated.
Frequency Response: 90 to 13,000 Hz (See Figure 1)
Polar Pattern: Supercardioid (See Figure 2)
Impedance: 150 ohms/Hi-Z, selectable
Impedance Change: Combined with on/off switch on stud (See instructions)
Output Level, 150 Ohm Impedance: -56 dB (0 dB=1 mW/10 dynes/square centimeter) High Impedance: -55.5 dB (0 dB=1 volt/dyne/square centimeter)
EIA Sensitivity Rating, 150 Ohm Impedance: -150 dB High Impedance: -150.5 dB
Diaphragm: Electro-Voice Acoustalloy
Case: Pressure-cast Zinc
Finish: Satin chrome
Dimensions: 181.0 mm (7.13 in.) maximum length, 38.1 mm (1.50 in.) maximum diameter (tapered shank)
Net Weight: 520 g (18.5 oz.), not including cable
Cable: 4.6 m (15 ft.), two-conductor, shielded, vinyl-jacketed, with Switchcraft A3F connector
Optional Accessories: 314E gray pop filter 360 gray windscreen 400 desk stand 456 carrying case PLC-25X 25-foot cable with A3F and A3M connectors PLC-25P 25-foot cable with A3F and quarter-inch phone plug connectors PLC-25T 25-foot cable with A3F connector at one end and unterminated at the other end
Quoted from Electro-Voice Model 664A Dynamic Supercardioid Microphone instructions, Copyright 1983, Gulton Industries, Inc. Part Number 530289-322. Published in 1983.