JL Audio Fathom f212 powered subwoofer Page 2
All set-and-forget inputs and controls are on the rear panel, which is also identical to the f113's. These include: three XLR connectors: two for signal inputsumming circuitry in the Fathom's input circuitry converts stereo signals to monoand a third output to link to a slave subwoofer; a pair of line-level RCA input jacks, the left for receiving a mono bass signal; the Power On/Off switch; the mains AC voltage selector; and the IEC power socket. A Master/Slave switch allows the ARO system to automatically optimize the response of a system with multiple subwoofers. The Slave position defeats all user-definable signal processing and the Master level control.
The Fathom f212's fit'n'finish are identical to the f113's, including a superb sprayed-on finish of glossy black lacquer. The hardware and connections are easily accessible and ruggedthey look as if they'll last for years.
Setting up two Fathom f212s
A single huge shipping pallet with two 300-lb crates strapped to it was delivered to my garage door. Attached to each create was a bright orange warning: "Due to the weight of the Fathom subwoofer, please exercise caution while unpacking and positioning it to prevent injury. If possible, enlist the help of a second person to facilitate the process. To minimize the risk of injury, bend your knees and lift with your legs, not your back."
I've gotten less proud since I've begun to collect Social SecurityI asked for help. JL Audio responded by sending along a strapping young sales representative, who hoisted each crate up the short flight of carpeted stairs into my listening room, then carefully unpacked both. Putting old towels under the subs to protect my wooden floors, I slid an f212 into each of the room's front cornersthe same places from which I'd auditioned the f113s. My Quad ESL-989 speakers, which would handle all musical information above 100Hz, were positioned 8' apart, 5' in front of the wall behind them, 3' from the sidewalls, and toed-in slightly toward my listening chair 8' away. A Mark Levinson No.334 stereo amplifier drove the '989s to high volumes in my lightly damped, 4056-ft3 listening room. Because the JLA subs lack a high-pass filter, I provided bass management with an outboard electronic crossover, the Bryston 10B SUB.
I decided to set up the subwoofers in stereowhich the f212's manual calls the "Master/Master configuration"because it had been what worked best with the f113s.
I reviewed the notes I'd taken while setting up the Fathom f113s in Master/Master mode, and the same procedure worked just fine with the Fathom f212s. The full-range audio signal was run from my Bryston BP26 preamplifier to the Bryston 10B SUB crossover via a pair of balanced interconnects. After setting the 10B SUB's right and left high-pass-filter switches for the Quads to 100Hz and its low-pass filters to 70Hz (all filters set to 18dB/octave), I set it to provide the f212s a stereo low-pass subwoofer output. Balanced interconnects were run from the 10B SUB's high-pass outputs to the Mark Levinson No.334, which then drove the Quads. The crossover's low-pass outputs were connected via balanced interconnects to each f212's XLR input jacks, their rear-panel switches set to Master.
Full Fathom Quad
As before, I used the internal signal generator and virtual spectrum analyzer of my Velodyne DD-18 subwoofer to match the f212's output with those of the Quad ESL-989s, which made this phase of the JLAs' optimization go smoothly and quickly: While producing no sound from its own woofer, the Velodyne generates a line-level test signal that sweeps from 20 to 200Hz. (See my review of the Velodyne in the June 2004 Stereophile.) I fed this signal to the Aux input of my Bryston preamp to be played through my stereo system, then captured the f212's in-room output with the Velodyne's measuring mikeplaced on the back of my listening chair at my seated ear height of 37"and displayed it on a small TV monitor.
I first tested the Quads full-range by muting the Bryston 10B SUB's low-pass outputs, which silenced both subwoofers. The result was a clean response that rolled off by 10dB from 85 to 35Hz (fig.1). I then measured the unequalized output of the f212s, which was flat from 20 to 60Hz, with a small peak evident at 50Hz before it started to roll off (fig.2).
Fig.1 Quad ESL-989s, no subwoofer, in-room response, 20Hz200kHz (25dB vertical range).
Fig.2 JL Audio Fathom f212s, uncorrected in-room response (25dB vertical range). Notice 50Hz peak.
To match levels between the Quads and f212s, I switched the Quads back in circuit, then turned down the right f212's Master output level to visually match the sub's output (about 9 o'clock on the f212's rotary control) to that of the Quads, as eyeballed on the TV screen. Later, I further fine-tuned the balance to produce clean bass-drum strokes without overhang on "Cosmo . . . Old Friend," from James Horner's soundtrack for Sneakers (CD, Columbia CK 53146). I found that the tightest bass-drum sound was produced at the 0° Polarity setting. I wrote down the switch positions, then carried out the f212's ARO room-EQ procedure.