Electro-Voice 12TRX
A 12-inch triaxial reproducer that packed a woofer, a midrange cone, and a diffraction-horn tweeter into one concentric frame. It cost a lot.
Overview
The 12TRX makes sense once you know what Electro-Voice was doing with the "TRX" badge. It was an integrated three-way loudspeaker built around a single 12-inch frame, with the drivers arranged concentrically instead of scattered across a baffle. The idea was full-range sound from one cutout: a woofer, a Radax midrange section, and a compression tweeter firing through E-V's patented diffraction horn, all on a common axis. Electro-Voice billed this as a way to avoid the masking effects and imposed distortions of separate multi-way systems. The marketing copy promised "phenomenal bass response, full-bodied mid-range and silky-smooth upper octaves to the highest audible frequencies."
The feature set was unusual for its day. The 12TRX shipped with the X-36-1 crossover network and the AT-37 brilliance control included. The AT-37 is a separate tonal balance adjustment that could be mounted remotely, so the listener could tailor response to room acoustics without crawling behind the cabinet. That sounds minor on paper, but in a real listening room the difference between a bright corner placement and a damped one can be several dB of treble.
The published numbers put the 12TRX at a nominal 16 ohms impedance, with a frequency response of ±5 dB from 30 to 15,000 cps in the recommended enclosures. A ±5 dB window is not a flat-response claim in the modern sense, and E-V was upfront about that. The spec is tied to "recommended enclosures," meaning the folded-horn cabinets the company sold alongside the driver. Drop a 12TRX into a random box and those numbers no longer apply. The 30 cps low end is impressive on paper for a 12-inch driver, but it depends entirely on the horn loading the enclosure provides.
Physically, the 12TRX measures 12½ inches in diameter and 8 inches deep, with a 3½-pound magnet structure and a shipping weight of 38 pounds. The frame is die-cast, and E-V leaned on that heavily in its advertising. The argument was that a one-piece die-cast frame holds alignment of every moving part and resists the twisting, bending, and sagging that can add distortion or shorten driver life. The voice coil is edge-wound, a design E-V claimed delivered 18 percent more efficiency than conventional winding. Whether that 18 percent meant audibly more output is hard to verify decades later, but the edge-wound coil was a real engineering choice.
The price record shows some drift. Early advertising listed the 12TRX at a $190.00 list price with an audiophile net of $114.00, bundled with the crossover and brilliance control. By the mid-1960s, E-V's own ads positioned the 12TRX alongside the 12TRXB as the premium tier above the budget E-V/Wolverine LT12, with the 12TRX carrying a $120 figure against the LT12's $36. That is more than three times the price. E-V's copy leaned into the comparison, arguing that the LT12 shared "almost every luxury feature" of the more expensive three-way 12-inch speakers and that the difference between the two was "in degree, not in basic design." Audio (December 1965, p.74) ran that same comparison, with the 12TRX and 12TRXB held up as the reference point against which the cheaper LT12 should be judged. It is an odd piece of advertising, since the company is telling you its budget speaker gets you most of the way to its flagship.
The enclosure matters more for the 12TRX than for a typical bookshelf driver. E-V explicitly recommended folded-horn cabinets, and the company's own literature names the Aristocrat kit (Model KD-6) as the folded-horn corner enclosure designed for 12-inch speakers including the 12TRX. The Aristocrat was a corner-loaded horn, and E-V claimed smooth reproduction down to 35 cps with "remarkable purity and efficiency" when the 12TRX was installed in it. The ±5 dB, 30-15,000 cps response figure was measured in that configuration, not in a sealed box or a ported box, but in a proper horn. Buyers who pulled a 12TRX from a console or dropped it into a generic cabinet were not getting the speaker the spec sheet described.
By 1973 the 12TRX was still appearing in Electro-Voice's trade-show lineup, listed alongside the SP12, SP12B, and 12TRXB among the loudspeakers shown on the Gulton stand. That is a long production run. The 12TRX shows up in E-V advertising from the mid-1950s through the early 1970s, which suggests the design held up commercially even as the catalog expanded around it. The 12TRXB, its near-twin, gets more attention in the secondary literature and in E-V's own later advertising, but the 12TRX was the original of the pair and carried the higher price in the early years.
For collectors today, the 12TRX is a niche piece. It is a component speaker, not a finished system, so most surviving examples are either still in Aristocrat or Regency cabinets, or sitting loose and waiting for someone to build them a proper horn. The 16-ohm impedance is friendly to tube amps and to the high-impedance taps on vintage receivers, but it means the 12TRX won't extract full power from a solid-state amp optimized for 8 or 4 ohms. The included crossover and brilliance control are frequently missing from loose drivers, and a 12TRX without its X-36-1 network is only half the system E-V sold. The die-cast frame and heavy magnet structure are built to survive, but the cone and surround are now decades old, and any 12TRX still in service should be inspected for surround deterioration before being driven hard. Prices are not well documented in the available sources, and buyers should treat any listing as a project until proven otherwise.
The 12TRX came from a time when the integrated concentric driver was seen as the answer to the multi-way alignment problem. E-V built a premium 12-inch three-way and then spent its advertising budget arguing that the cheaper model got you most of the way there.
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