The Electro-Voice Model 676 Variable-D Dynamic Cardioid Microphone
The Electro-Voice Model 676A Dynamic Cardioid Microphone in TV Gray.
Description and Applications A dynamic cardioid microphone, the Model 676 is designed for recording, public address, and communications uses. It provides a sophisticated version of the well-known Electro-Voice Variable-D principle, Continuously Variable-D (CV-D), which phases out unwanted sound from the back, regardless of frequency. The CV-D principle makes use of a slotted tube, coupled to the back of the 676 diaphragm. The tube’s apparent length varies inversely with sound frequency, permitting it to phase out unwanted sound from all portions of the audible spectrum for maximum front-to-back cancellation.
Another important feature of this microphone is its built-in three-position bass tilt-off control which, by means of a slide switch integral with the microphone case, allows selection of flat response or bass attenuation tilted off from about 800 cps, with response down either 5 dB or 10 dB at 100 cps. This feature permits attainment of better average sound levels, greater intelligibility, and improved control over feedback. The center position of the switch provides a flat low-frequency response for small rooms and many recording applications. When the 676 is used as a public address microphone, however, especially in large rooms, the 5 dB or 10 dB attenuation will be found helpful to overcome unwanted room reverberations. In recording use, low-frequency attenuation may or may not be required, depending upon the program material and acoustical environment. Often the bass-tilt feature will be of value, even when recording music, since it permits control over the boomy, over-reverberant characteristic of large rooms and low-frequency noise usually possible only in professional studios.
The Electro-Voice Model 676A Dynamic Cardioid Microphone on the Electro-Voice Model 420 Desk Stand.
Figure 1 — Frequency response
Figure 2 — Polar pattern
Figure 3 — Dimensions
Wiring The Model 676 may be used at either 150-ohm or high impedance. The desired impedance is easily selected by a simple change made at the cable connector. (Refer to Figure 4.) The microphone is supplied wired for high impedance operation unless otherwise specified. Most ordinary public address amplifiers and tape recorders are equipped with high-impedance inputs, making the 676 an ideal choice for such units. Using a mic having high impedance is not recommended, however, when the cable length exceeds twenty feet. High impedance cables beyond this length are likely to impair audio quality through loss of high-frequency response, and pick up extraneous noise. Use of the 676 at low impedance (150 ohms) entirely eliminates this problem. At this impedance setting literally hundreds of feet of cable may be used with no signal quality loss. The E-V Model 502A transformer may be used to match a low-impedance 676 to a high-impedance input.
Figure 4 — Wiring diagram
Although its box is water damaged, the “A” in “676A” is still clearly visible.