Electro-Voice SP8B
An eight-inch coaxial that sold for $29.50 and ended up in the corners of a thousand living rooms - the Radax Super-Eight.
Overview
The SP8B was not the flagship of the Electro-Voice line. It was the cheap one. A 1957 Electro-Voice advertisement in Audio (May 1957, p.87) listed the SP8B at a net price of $29.50. That sat at the bottom of a catalog that ran up to $115 low-frequency drivers and $145 triaxial systems. It was the eight-inch Radax a budget-minded builder could actually afford, and Electro-Voice built an entire enclosure ecosystem around it.
The HiFI-Stereo (1963, p.95) listing for the "Radax Super-Eight" lays out the design plainly. It is a bookshelf ducted-port bass reflex system built around an 8-inch low-frequency speaker paired with a compression driver on an exponential horn tweeter. A quarter-section LC network divides the frequencies at 1600 cps, with a high-pass filter at 4000 cps and a level control for the tweeter. Impedance is 16 ohms, and the driver is rated at 25 watts program material or 15 watts sine wave. The same listing gives a response of 50-12,000 cps, ±5 db. It notes the enclosure is ¾-inch stock tuned to 25 cycles by a tubular ducted port, with response essentially uniform from 45 to 12,000. Those are modest numbers. The SP8B was the driver you bought when you wanted coaxial point-source behavior without spending triaxial money.
Collectors like the SP8B because Electro-Voice thought of it as part of a system. The company did not sell it as a bare component and leave the buyer to figure out the box. It appears by name in the enclosure literature. A 1956 advertisement in Audio (October 1956, p.87) describes the Baronet Kit, a folded-horn corner enclosure "designed for use with E-V Model SP8B 8-in. Radax speaker," with the option of adding an E-V 135 or 135B Super Sonax UHF driver for a three-way system. The same ad pitches the Coronet as an 8-inch coaxial system built around the SP8B. The enclosure kits were designed around the driver's low-frequency resonance.
That resonance is documented. A 1971 construction feature in Electronics Illustrated (November 1971) used the SP8B as the premium driver in a DIY horn-loaded bass reflex project, noting that "the low-frequency resonance is around about 45 cps." The enclosure's flare rate and port size were calculated for a 42-cps cutoff to match it. The article contrasted the SP8B against a budget Olson driver resonating at 35 cps, and the author was explicit that the more expensive system used the Electro-Voice.
The SP8B also turns up in the used market of its own era as part of complete Electro-Voice systems. A 1967 classified in Audio (June 1967, p.87) offered a pair of Electro-Voice Georgian 400 systems - each loaded with an 18WK, an SP8B, a T25A, and a T350 - at $300 apiece. So the SP8B was the midrange-and-up coaxial in a four-way floorstanding system, not just a standalone bookshelf speaker.
Owners report that the SP8B likes a properly matched enclosure and does poorly in a generic one. The 45-cps resonance means it wants a box tuned to work with it, which is why the Baronet and Coronet kits existed. The 16-ohm impedance is friendly to tube amplifiers of the period, and the 25-watt program rating is honest about what the driver will take. Collectors note that the compression tweeter with its level control is the part that most often needs attention after six decades. Because the mounting is coaxial, a failed tweeter takes the whole driver out of service rather than just the top octave.
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