Electro-Voice BK-1
A diecast workhorse that used proximity effect to fight feedback, and stayed in EV's catalog long enough to ride along with a wireless system.
Overview
The BK-1 is a Single-D electret condenser cardioid microphone. The body is zinc diecast with an aluminum battery compartment cover, finished in non-reflecting black paint. It measures 190.5 mm (7.50 in.) long, not including the cable connector, with a shank diameter of 25.4 mm (1.0 in.) and a maximum diameter of 50 mm (1.97 in.). It weighs 343 grams (12 oz) with battery but without cable. You notice that in the hand, which is the point of a diecast case in live work. The grille screen is Memraflex, a tempered spring steel, and a built-in Acoustifoam pop filter sits behind it.
What sets the BK-1 apart from the pile of black cardioid condensers is its variable low-frequency response. Maximum bass comes in close-up use - the manual specifies the microphone at 1/4-inch from the source - while minimum bass occurs at distances greater than 24 inches. That's not a quirk to be managed. It's the design brief. Electro-Voice's own documentation calls the mic uniquely adapted to live entertainment use where reflected sound causes ringing and feedback, and presents the variable bass response as a second layer of feedback protection on top of the cardioid pattern itself. The reasoning is straightforward. When the performer works close, the voice level at the mic rises, the amplifier gain can be proportionately reduced, and the system becomes less sensitive to reflected sound from the loudspeakers. The boosted low end at close range doesn't apply to distant reflections, so the feedback path stays attenuated. The manual calls the combined effect exceptionally effective for stage and nightclub work.
The variable response cuts both ways, and EV's documentation says so. For musical pickup, the same characteristic that fights feedback lets an engineer get clean bass at 24 inches or more, then move the mic in a few inches to add low end. There's also an explicit caution: with the lips closer than 4 inches, bass response increases dramatically, and the resulting signal may exceed the input range of a mixer or amplifier, causing distortion. The fix is an in-line attenuator or pad between mic and mixer. The mic will happily overload an input that isn't padded for it.
The electret element is a permanent-charge design, so no polarizing voltage is needed. The small current draw of 3.5 mA exists only to power the FET impedance converter, which steps the electret head's very high impedance down to something a preamp can use. Power comes from a 4.5-volt battery, reached by unscrewing and pulling away the rear sleeve to expose the battery clips, or from any phantom supply between 24 and 48 volts. EV recommends alkaline batteries - Eveready No. 523 or Mallory PX 21 - for shelf life and reduced leakage risk, and notes that at 3.5 mA it's common to see 150 hours or more of battery life. Output declines gradually well before the battery dies completely, so a replacement can usually be made without interrupting a program. The mic can also run from phantom power with a battery still installed, with no effect on performance. The on/off switch mutes the microphone in either mode. In battery mode it also opens the power connection to conserve the cell.
The frequency response is specified at 50 to 18,000 Hz, with a 150-ohm balanced output, an output level of −50 dB (0 dB = 1 mW/10 dynes/cm²) and 2.5 mV/Pascal at 1 kHz, dynamic range of 100 dB, and an equivalent noise level of less than 30 dB typical, A-weighted. EIA sensitivity is rated at −144 dB. EV states that the electret generating element's output is not appreciably affected by temperature extremes from −17.8°C (0°F) to 54.4°C (130°F) or by humidity extremes. The maintenance instructions still warn against leaving the mic in open sun or hot environments approaching or exceeding 54.4°C, since heat shortens the life of the generating element. Each BK-1 shipped with an Electro-Voice Model 323 stand clamp and a zippered vinyl carrying pouch.
DB-Magazine (July 1984, p.43) noted the BK-1 had recently joined EV's product line, describing it as departing from EV tradition in several respects — including its unique physical profile and black finish — while combining popular features from other mics in the line. The same item highlighted the proximity effect that tailors low-frequency response with working distance, and cited the mic's high sensitivity, smooth peak-free response, and cardioid pattern as the basis for its rejection of off-axis and reflected sound. That's an accurate summary of the design intent, and it matches what the manual claims for the mic in stage use.
Fifteen years after its introduction, the BK-1 was still showing up as a premium option. Mix-Magazine (February 1999, p.141) listed the BK-1 condenser as one of the premium-quality microphone choices offered with Electro-Voice's R200 UHF wireless systems, alongside the N/D157 and N/DYM models. An EQ-Magazine (February 1999, p.101) item carried the same R-Series wireless listing. So a wired electret condenser from the early 1980s was a handheld capsule option on a late-90s UHF wireless system.
Warranty coverage on the Professional, PL, and BK Series was unusually generous for the period: two years against malfunction from any cause, no time limit at all against malfunction in the acoustic system due to defects in workmanship and material, and three years on active electronics for parts and labor. The exclusions are the usual ones - finish, appearance items, cables, cable connectors, switches, abuse, and operation outside specified conditions. Repair by anyone other than EV or an authorized service agency voided the guarantee.
The BK-1 is a live-sound tool first and a studio mic second. The cardioid pattern and the distance-dependent bass make it work well on a loud stage, and the 150-ohm balanced output and 100 dB dynamic range give it headroom. Use a pad if you plan to work it tight. Watch the battery compartment cover, since the aluminum sleeve unscrews to expose the clips. The Model 323 stand clamp and vinyl pouch are frequently missing from used examples. The diecast zinc body and the electret element's temperature and humidity tolerance mean a BK-1 that's been stored badly is more likely to need a switch cleaning than a new capsule.
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