JBL LE15A

The LE15A is a 15-inch low-frequency transducer — a woofer, plain and simple — that JBL built for professional studio monitoring, as noted in High-Fidelity (March 1968, p.89). It was the lowest-frequency component of the DMS-1 monitoring system, and it also found its way into the L300 Summit speaker system, as well as the Everest and Ranger-Paragon systems. The related LE15B, introduced in 1964, was a variant built specifically for the Paragon, with a different cone, spider, and voice coil. The LE15A was later succeeded by the model 136A.

Most of what's documented about the LE15A comes from a single JBL engineering note (Audio Engineering Notes 2-72), which gives a remarkably candid picture of the driver's capabilities and limits. The LE15A uses a 4-inch edge-wound aluminum ribbon voice coil and a magnet structure with 14,000 gauss flux density. Free air resonance is 30 Hz. JBL was blunt about its top end: there is no usable response above 1500 Hz, and if you run it full range, output is down 10 dB at 6000 Hz relative to 500 Hz. The cone has a resonance at 1500 Hz that must be restricted, and JBL recommended crossing over at or below 1200 Hz for best results.

Power handling is rated conservatively at 25 watts of program material or 50 watts of white noise. JBL noted that higher levels could be applied with bass and treble shelving controls, but warned that extended use at the full rated power of 150-watt amplifiers is dangerous — while adding, tellingly, that "the LE15A will take as much power as any other bass system."

JBL specified a closed-box enclosure of 6 cubic feet or larger, lined with one pound per cubic foot of fiberglass. Sensitivity is listed at 87 dB SPL at 20 feet with 1 watt input, including half-space room effect and 4 dB cabinet edge effect. Maximum acoustic output is stated at 113.5 dB SPL at 30 feet in half-space. Nominal impedance is 16 ohms. The driver weighs 30 lb and requires a 15-1/2-inch mounting hole.

No original price, exact production years, or owner-review commentary have surfaced in the available documentation. The record is technical and thin, but what exists is unusually specific about how this driver was meant to be used — and, just as importantly, where its limits were.

Type: 15" low-frequency transducer (woofer)
Nominal impedance: 16 ohms
Free air resonance: 30 Hz
Flux density: 14,000 gauss
Voice coil: 4" edge-wound aluminum ribbon
Power capacity: 25 W program / 50 W white noise
Sensitivity: 87 dB SPL at 20 ft, 1 W input
Recommended enclosure: 6 cu ft closed box, 1 lb/cu ft fiberglass lining
Net weight: 30 lb