JL Audio Fathom f212 powered subwoofer
The Fathom f212
Finally, they offered me a pair of their newer twin-driver model, the Fathom f212. The Fathom f212 resembles the Fathom f113: both are self-powered, sealed-system subwoofers whose drive-units have prominent rolled surrounds, and both feature an automatic internal room optimizer for single-band adjustments. Both models also feature the same reference sensitivity of 166mV in to produce 105dB SPL at 50Hz output at 1m. All inputs are separately buffered and can be used simultaneously (to connect, for instance, a single sub to separate two-channel and surround systems). The rear panels of both models boast the same sets of inputs, outputs, and controls.
However, the Fathom f212 uses two smaller 12" drivers wired in parallel rather than the f113's single 13.5" unit, and has a more powerful (3kW peak) amplifier, with "massaged" electronics to manage the twin drivers. The f212's larger total diaphragm area is said to allow it to produce more output for less relative excursion, with greater ultimate dynamic-range capability than a single-driver sub. As a result, the f212's cabinet is about 12" taller, 2" narrower, and 1" deeper than the f113's, and weighs 90 lbs more.
In an e-mail to me, JLA senior research engineer Brett Hanes said: "Comparing diaphragm configurations, the f212's 168 square inches of cone area (effective displacement of 574 cubic inches) means it has 57% more cone area than the f113's 107.35 square inches of cone area (effective displacement of 286 cubic inches). The combination of larger cone area, greater displacement, and higher amplifier power output gives the f212 a distinct edge in the lowest octave. This encompasses not only higher ultimate output, but also more linear operation for a given output."
The subwoofers JL Audio makes for trucks and boats take beatings and shakings never experienced by home audio gear. As a result, JLA's loudspeaker drivers must be mechanically rugged. The Fathom f212's 12" drivers are built to the same massive scale found in the Fathom f113's driver; ie, they offer a maximum 3" peakpeak excursion, with a large-radius roll surround that covers the mounting flange to maintain control of the cone, along with what JL calls a Floating-Cone Attach Method to maintain optimal voice-coil alignment at all sound levels. To handle the internal stress of high-powered subwoofing, JLA uses an enclosure reinforced with two donut braces parallel to the front baffle and built of CNC-cut, 1"-thick MDF. The f212's class-D amplifier is attached to the inside of the rear panel.
Controls in front, plugs in back
Like the Genelec HTS4B subwoofer, which I reviewed in November 2005, the Fathom f212 lacks a high-pass filter to shape the bass response of the main speakers. This is because all surround-sound preamplifier-processors perform the high-pass filtration and bass management before the audio signal reaches the sub.
The Fathom f212's controls are under its removable grille, on a narrow panel of brushed aluminum at the top of the front bafflevery handy. The controls are identical to the Fathom f113's: toggle switches for Power (On, Off, Auto Sensing); JLA's Automatic Room Optimization, or ARO software (Demo, Defeat, Calibrate); and Polarity (0°/180°); and rotary controls for Phase (0180°, continuous), Low-Pass Filter (30130Hz), and Extended Low Frequency (ELF), the last for adjusting the slope of a 25Hz filter within a range of 12dB to +3dB, to damp subsonic room modes. There is also a ground-lift switch to reduce hum with unbalanced inputs.
Also supplied are a well-written manual, a calibration microphone attached to a 20' cable, a pair of gloves, and four 50mm sliders to allow the subwoofer to be moved across wooden floors without scratching its finish or the floor.
Footnote 1: I suspect that JL Audio did know of a better subwoofer, and that it might have been their Gotham g213, with its twin 13.5" drive-units, huge size (34.13" H by 21.5" W by 24" D) and weight (305 lbs), and 3800W RMS peak output. But though I tried to convince them otherwise, JLA refused to lend me a pair of Gothams for review, stating that the logistics of shipping, delivering, and setting up two such behemoths were too daunting.