Electro-Voice 828HF
A diffraction horn driver that lived its life two at a time, buried inside the mid-bass section of a four-way horn system.
Overview
The 828HF is not a speaker you buy on its own. It is a mid-bass driver, and the surviving documentation places it inside the Patrician IV, Electro-Voice's four-way horn system. Two of them ride a separate wood-and-phenolic diffraction horn covering 200 to 600 cycles. The documentation treats the 828HF only as a step in that larger job: install the pair with terminals facing forward, screw them into the re-entrant horns, tie their T1 terminals together and their T2 terminals together, then run a black lead off the left unit's T1 and a red lead off its T2 out past the front edge of the 200-cps horn assembly.
That's the whole documented life of the thing. No standalone review, no spec sheet of its own, no cabinet it was sold to sit in by itself. If you find one loose, it almost certainly came out of a Patrician IV or somebody's home-built copy of one.
The period coverage does establish the design logic behind putting two of these on one horn. The mid-bass section in the Patrician IV was deliberately built as an indirect radiator rather than a straight horn, and the horn load was made of wood and phenolic tubes. Reproduction down to 200 cps was "handled much more satisfactorily than a horn assembly made of metal." The 828HF pair feeds that wooden horn. Above them, a T25A driver exhausts into a 600-cps 6HD diffraction horn to cover 600 to 3,500 cps, and a T35 Super-Sonax takes everything above 3,500. Below them, an 18WK handles the first three octaves.
The 828HF pair only has to cover an octave and a half, 200 to 600 cps. Two drivers sharing one horn means each does less work in the region where horn loading is hardest to get right. The X2635 crossover network split the amplifier's power into four separate portions, and the design intent was to eliminate upper-harmonic and intermodulation distortion from one driver in the region covered by the next. The record doesn't answer with measurements whether it succeeded.
Electro-Voice's own advertising documents the 828HF's price. A 1957 E-V catalog page listed the "Model 828HF with A8419" at a net of $28. That puts it in context: a $28 mid-bass driver in a system whose low-frequency 18WK ran $115 and whose T35B very-high-frequency unit ran $21. It was a component, priced like a component, in a catalog that also sold complete speaker systems and enclosure kits. Contemporary Electro-Voice advertising in the period press reinforced this component-level positioning. The company promoted its extended-range integrated three-way loudspeaker systems alongside its individual low-frequency drivers, and listed drivers such as the 18WK and 15WK at net prices of $115 and $85 respectively (Audio May 1957, p.87; High-Fidelity May 1957, p.19).
Collectors chasing Electro-Voice horn gear tend to fixate on the big woofers and the Super-Sonax tweeters. The 828HF is the part that makes the mid-bass work, and it's the part most likely to have been separated from its horn and lost in a basement. The A8419 designation attached to it in the catalog refers to the horn it was paired with, so a driver found without that horn is only half the assembly. Expect to hunt for the pair, and for the wooden diffraction horn, separately.
One note for anyone building or restoring a Patrician IV around these: the manual is emphatic about airtightness at the joint where the diffraction horn sub-assembly sits atop the K horn. Use adhesive-backed sponge rubber weatherstripping, half by three-quarters of an inch, along the inner outline, plus glued muslin or broadcloth strips over interior joints, or wood filler. Leaks there will undo the horn loading the 828HF pair depends on.
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