Electro-Voice Model 666
A dynamic cardioid that got its pattern from three ports instead of two elements, and stayed on the market long enough to become a broadcast workhorse.
Overview
The Model 666 is a dynamic cardioid built around a single moving element. Most cardioids of the early 1950s got their pattern by combining a pressure-type element with a velocity-type element. Two transducers, out-of-phase from the rear, adding from the front. Electro-Voice did the phase cancellation acoustically inside the housing instead. The company called it Variable-D, and it used three sound entrances placed at different distances behind the diaphragm. That gave a cardioid that needed only one element, no closely associated auxiliary amplifier, and essentially no proximity effect.
That last claim is the one working engineers cared about. A single-port cardioid gets bassier as the source moves in close, and the operator can only back off. The 666's multi-port arrangement was designed to cancel rear-arriving sound uniformly across the spectrum rather than at one compromise frequency. Audio (May 1955, p.72) put the front-to-back cancellation at better than 20 dB in open air. It noted the figure would be modified somewhat in reflective rooms but was still enough to allow working at much higher gain before feedback. That helped for PA work and for broadcast with a live audience.
The specs are respectable for the period and consistent across E-V's own literature. Frequency response is quoted as 40 cps to 15,000 cps ±2.5 dB in the 1961 catalog listing. A 1966 advertisement describes the range as peak-free from 30 to 16,000 Hz. The tighter 40-15,000 cps ±2.5 dB figure is the more conservative and better-documented one. Output level sits at -58 dB in the 1961 and 1966 literature, though a 1955 catalog page lists -55 dB, so expect some variation in print depending on the year and the measurement reference. Impedance is internally tapped for 50, 150, or 250 ohms, shipped wired for 150 ohms, and readily changed in the field.
The diaphragm is E-V's Acoustalloy, a material the company marketed hard as indestructible. The housing carries a blast filter to keep wind and plosives from bottoming the element. Finish is a non-reflecting gray epoxy, "TV gray" in the catalog language of the day, which says where E-V expected these to be seen. Weight is listed at 11 ounces in the 1954 and 1955 literature and 1 pound in the 1961 listing. The discrepancy is almost certainly a shipping-versus-bare weight question rather than a design change. Dimensions in the 1954 ad read 7½ x 1½ x 1½ x 1½, and the microphone shipped with a detachable clamp-on swivel stand coupler and 20 feet of cable.
Pricing moved a lot over the run. The 1954 Audio advertisement lists the Model 666 at $245, with the Model 366 boom mount at $40, the Model 300 stand coupler at $10, and the Model 420 desk stand at $20. By the 1961 catalog the user net price had dropped to $149.95. That's a steep decline for a microphone that hadn't fundamentally changed, and it says more about the shrinking professional-audio market of the late 1950s than about the 666 itself.
The 666 was not the top of the line, and E-V was candid about this in its own comparison charts. The 1961 listing shows the 666 at $149.95 against the 644 "Sound Spot" at $110, the 664 cardioid dynamic at $85, and the 636 omnidirectional dynamic at $72.50. The 666 sat above those, but the same catalog page carries the Neumann U-67 condenser with its switchable cardioid/omni/figure-8 patterns and 20 cps to 16,000 cps range. Buyers who needed a condenser went to Neumann. Buyers who needed a rugged dynamic that would survive a broadcast booth went to E-V.
Durability runs through the period copy. The 1955 Audio write-up describes the design as combining the ruggedness of a single dynamic element with the new acoustic principle, eliminating pickup of ambient noise, unwanted reverberation, and equipment rumble. That's advertising language, but the engineering claim behind it is sound: one element instead of two, fewer things to fail. Owners report these microphones surviving decades of studio and remote work, and the Acoustalloy diaphragm has a reputation for taking abuse that would destroy a thinner foil.
By the mid-1960s the 666 was a fixture rather than a novelty. A 1966 E-V advertisement calls it one of the most popular directional microphones on the market. The same copy walks through the three-port system in detail. Side windows feed the back of the diaphragm through short paths that pass only highs. A top port with a longer path and added filtering handles the midrange. A rear port with an even longer path handles the lows. Each provides roughly 20 dB of rear cancellation at its band. The ad is pointed about the alternative: most single-port cardioids, it argues, are "actually omnidirectional at one frequency or another." That's marketing, but it comes with a testable claim.
The 666 stayed in E-V's catalog long enough to appear in trade advertising through the 1960s and into later reprints. DB Magazine ran the three-port illustration as late as November 1983 (p.46). The microphone was sold alongside a deep accessory line of boom mounts, stand couplers and desk stands, and complete examples with the original swivel coupler and cable command more than bare microphones.
On the used market, the internal impedance taps are a common point of confusion. A 666 wired for 50 ohms will sound thin and quiet into a modern 150-ohm input until it's re-tapped. The gray epoxy finish shows handling wear readily. The blast filter can degrade with age. And as with any 60-plus-year-old dynamic, the element itself is the wild card. A clean, unmolested example is worth seeking out over a cosmetically perfect one that's been opened up.
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