Electro-Voice Model 668
Thirty-six microphones in one, at the end of your boom - if you can find one that still has its programming pins.
Overview
The Electro-Voice Model 668 is a dynamic cardioid microphone with a passive equalizer and both low- and high-pass filters built into the case. It needs no power supply. Electro-Voice's own advertising billed it as "just like having 36 microphones in one, at the end of your boom." Match the computer-style programming pins to the color-coded jack field inside the body and you get any combination of flat response, bass rolloff, treble rolloff, treble rise, and either an 80 cps or 8,000 cps cutoff. Audio (September 1965, p.68) ran the announcement with the same pitch, noting the built-in passive equalizer matched response to need without losing output level and mixed cleanly with other microphones.
The concept came out of a real studio problem, explained by E-V's own microphone project engineer Marvin C. Negley in a period write-up. Engineers were routinely strapping external equalizers and filters onto wide-range condensers to tame specific acoustic situations or artistic whims, and on complex multi-mic pickups the outboard gear piled up fast. The 668 folded that entire network into the microphone body. The element's response was deliberately shaped to anticipate the losses the filter network would introduce. Negley was explicit that the element without the filter would be "completely unusable," and the filter section useless with any other element. It's a total-instrument design, not a mic with a tone control bolted on.
The filter specs show what the 668 was actually for. The 80 cps high-pass kills rumble and electrical noise on just the affected microphone - at 60 cps you get 25 dB of attenuation while response is down only 3 dB at 80 cps. The 8 kc low-pass does the same job at the top end for high-frequency problems. Flat response runs 40 to 12,000 cps. All the possible curves are printed graphically on the case, so you can see what you're selecting before you commit a pin.
The polar pattern got just as much engineering attention. The 668's cardioid is symmetrical in every plane with strong rear cancellation at every program setting, achieved through two independent Continuously Variable-D systems (the design is covered by Patent No. 3115207). E-V claimed high output, quoted at -51 dBm, for distant pickup without added equipment or special cables. That is exactly the spec a boom operator cares about. The integral Acoustifoam windscreen and shock mount keep shadow problems down and allow noise-free fast panning indoors and out.
Physically it's a working tool. It weighs 1 lb, 11 oz, and is 9¾ inches long including the integral windscreen. Negley noted that fitting this much filter network into a microphone case would have been unthinkable a few years earlier, and only became practical with ceramic and tantalum capacitors and ferrite core inductors. E-V's own copy touted the weight as eliminating "fishpole fatigue" and counterbalancing problems.
The 668 was not a quick product. E-V states it came out of a three-year field testing program in movie and TV studios from coast to coast, and the company claimed it proved superior to every other boom microphone available. Buyers could check that claim themselves, since E-V offered a no-cost, no-obligation trial through its professional microphone distributors. The factory backed the hardware with an unconditional two-year guarantee against malfunction of any kind, even accident or abuse, plus the company's standard lifetime guarantee against failure of materials and workmanship.
The price was serious money for 1965: $495 list, less normal trade discounts, against $345 for the companion Model 667A, which is identical except that the sharp-cutoff filters and HF-rolloff were eliminated.
The Black Keys' Patrick Carney told Electronic Musician that the band's guitar-and-drum setup included "a couple Electro-Voice Model 668 dynamic mics on guitar amps" alongside the usual dynamics and ribbons. The mic was designed for studio boom work, so guitar cabinets decades later are an odd place to find it.
That's a nice vote of confidence in the 668's transparency at low levels, though it's worth noting the filter settings used aren't documented in the excerpt.
Anyone shopping for a 668 should confirm the pin set is complete and that the internal jack field hasn't been damaged by someone forcing a pin. The unconditional guarantee is long expired, and the Acoustifoam windscreen on any surviving example is decades old. Prices are not well documented in the available sources, so treat any listing as an as-found gamble until the pins are confirmed. The 667A is less flexible, but it is the safer buy for someone who actually wants to use the thing.