Electro-Voice Model 30W
A 30-inch cone, nine pounds of ceramic magnet, and bass you feel in your sternum before you hear it.
Overview
Thirty inches across and more than thirteen inches deep, the Electro-Voice Model 30W is not a woofer you install so much as a woofer you accommodate. It weighs 34 lbs., and 9 lbs. 4 oz. of that is ceramic magnet — a figure that tells you most of what you need to know about the design philosophy before you've read a single spec. This is a driver built to move a great deal of air slowly and cleanly, and everything about it follows from that goal.
The size has a reason. E-V's own engineering notes explain that at very low frequencies a cone travels slowly, so a typical 12-inch driver has to swing a long way to produce even moderate output - on the order of an inch and a half of excursion. Enlarge the cone to 30 inches and the same acoustic output needs only a fraction of the travel. Less motion means more linear operation, and more linear operation means lower distortion. The 30W's large phenolic-impregnated cloth spider and viscous-damped suspension were designed to keep that excursion linear well past the half-inch mark.
A cone this big took materials that didn't really exist when smaller woofers were being perfected. Paper and high-density plastic cones of the day were either too floppy or too heavy at this scale. E-V settled on molded expanded-bead foam polystyrene, which is light but unusually rigid. By carefully controlling thickness and density, they arrived at what the engineers described as a true piston woofer. Below 250 cps, they claimed, no cone breakup or flexing could be detected despite the 30-inch diameter. The motor is just as serious. It is a low-loss magnetic structure with 15,000 gauss of flux density across an unusually wide 0.082-inch gap. The gap is wide because it has to clear a heavy edgewise-wound ribbon voice coil. That flattened copper coil keeps DC resistance low for minimal power loss, and it rides on a polyester glass laminated cloth form built to survive the forces this driver generates.
E-V rated the 30W at a nominal peak of 240 watts and 70 watts continuous sine wave. Those were substantial numbers for the period, and a direct result of the work on mechanical strength, stress distribution, and heat control in the moving assembly. Audio (April 1964, p.3) ran the 30W as the subject of one of the company's engineer-written technical discussions. The piece calls it the logical extension of proven technique combined with the best modern materials available. Audio (October 1965, p.102) put the low-end claim more bluntly, describing the thirty-inch woofer as reproducing a 15 cps fundamental at full volume without doubling.
What the 30W was used for shifted almost immediately. It was designed with high-fidelity music reproduction in mind, but its bass capability pulled it into other rooms. Major pipe organ constructors adopted it as an electronic substitute for the bulky, expensive 32-foot pipes needed for the lowest registers, and it turned up extensively as a bass speaker in non-pipe organs. By the late 1960s musicians had noticed too. They were drawn to the extreme low range, the high efficiency, and the power handling, all of which promised new sounds at higher volume levels. An ad in HiFi-Stereo (February 1968, p.47) placed the 30-inch woofer in the Patrician 800, which E-V billed as one of the biggest loudspeaker systems going, with the line "sounds you can feel as well as hear."
Owning one is a practical matter. A 34-pound, 30-inch driver needs a baffle and a room that can host it, and the deep bass it produces will find every rattle in the house. The 30W shows up in the classifieds occasionally. A 1969 Audio for-sale listing offers one with the terse instruction to "make offer." These change hands as heavy, specific tools sought by organ builders, bass obsessives, and people chasing the bottom octave, not as shelf pieces. Buyers should inspect the foam cone carefully, and handle the magnet assembly with care, since it is nine pounds of ceramic.
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