Electro-Voice Sb 120a
A 34-pound bass module with a 400-watt amplifier and a 12-inch woofer that EV's own advertising insisted thinks it's a 15.
Overview
The Sb 120a is the powered half of Electro-Voice's System 200, the modular pro-audio rig the company launched at the Frankfurt Musik Messe in 1994. System 200 had three pieces: the Sx200 two-way full-range cabinet, the Xp200 system controller, and the bass module. The bass module came either as the passive Sb120 or, from October 1994, as this amplified Sb 120a. EQ (August 1994, p.71) reported the launch as a complete replacement for the S-200 cabinet, which had been EV's bestseller since it appeared a decade earlier. The Sb 120a isn't a standalone box. It's the low end of a deliberately integrated system.
The module's job was to take the Sx200's floor - roughly 80 Hz for the 12-inch EVM 12S in the full-range box - and drag it down toward 40 Hz. EV did it with a single 12-inch driver, the DL12sb. It has a shallow cone and a deep frame, which allows a peak excursion of nearly 7/8 inch. That's the mechanical reason a twelve can move enough air to impersonate a fifteen, and it's the claim EV leaned on hardest in its marketing. The integral 400-watt amplifier is optimized for that driver. It isn't a generic plate amp pressed into service.
The enclosure is the same compact, stackable, stand-mountable and arrayable box as the Sx200. That helps anyone hauling a small PA, since the sub stacks and flies with its full-range partner and doesn't need its own mounting scheme. Filtering is built in. A low-pass rolls off response above 180 Hz at 18 dB per octave, which keeps the module essentially omnidirectional and gives placement flexibility. A high-pass attenuates below 40 Hz at 6 dB per octave for infrasonic protection. Input is a combination connector that takes balanced three-pin XLR as well as balanced or unbalanced 1/4-inch plugs. A paralleled full-range output lets you route signal onward without a splitter.
The interesting part is the Xp200 controller the Sb 120a was designed to pair with. The Xp200's low-frequency profile circuit delays low frequencies slightly in time and sums them back with the direct signal. It's a sidechain trick that changes the relative levels of fundamentals and their harmonics rather than simply boosting bass. EV claimed overall bass output could rise by up to 12 dB without the smearing of conventional low-frequency boost, and a variable control let users tune the effect to taste and room. EV's own advertising billed the trio as "the fusion of space, sight and sound," which is marketing copy, not a verdict. The technical description behind it is more specific than most.
On the numbers, EV's promotional material described the Sb 120a as a 34-pound bass module. EQ (August 1994, p.71) rendered the weight as "344b," almost certainly an OCR casualty of "34 lb" in the original. Treat 34 pounds as the figure. A period distributor sheet listed the powered Sb120a at $1,050 each, against $600 for the passive Sb120, $850 for the Sx200, and $400 for the Xp200 controller. That's a serious outlay for a single bass box in 1994 dollars, and it explains why the powered module is the rarer piece today. Most buyers who sprang for System 200 likely did so in stages, and the passive version was the cheaper entry.
Anyone chasing one today should know the Sb 120a is only half a system without the Xp200. The controller's profile circuit is where much of the promised performance lives, and a bare Sb 120a driven from an arbitrary crossover will not sound like the brochure. The DL12sb's excursion capability is the mechanical core of the design, so a used example with a tired surround or a cooked voice coil has lost the one thing that made it work. The 400-watt amplifier is integral and model-specific, so a failed amp module is not a swap-in-and-go repair.