JL Audio Fathom f113v2 Subwoofer and CR-1 Active Crossover

A Great Subwoofer Made Better

Equipment report
JL Audio Fathom f113v2
JL Audio Fathom f113v2 Subwoofer and CR-1 Active Crossover

JL Audio is one of those companies that does one thing and does it well. In JL’s case, that “one thing” is designing and building some of the world’s best subwoofers. Over its 38-year history, JL has fanatically pursued technological innovation with a single, laser-focused purpose: reproducing the lowermost 2½ octaves with the highest fidelity.

JL Audio holds an astounding 38 patents on woofer design (with six more pending), including those for a particular cone structure, a voice-coil cooling system, and a method of bonding the surround and cone assembly to the voice coil and spider, to name but a few. In addition to these patented proprietary techniques, JL Audio’s products are packed with non-patented innovations that are, in my experience, unique in the loudspeaker industry. If you read the extensive technical material on JL Audio’s website, you’ll get an appreciation for just how geeky and serious these guys are about subwoofers.

The result of this intensive focus on a single product category is a range of subwoofers that deliver reference-class performance. The first JL Audio subwoofer I heard in my own room was the original Fathom f113, about ten years ago. The system was dual-purpose (stereo and home theater) and equipped with reference-quality components. The f113 performed exceptionally in either two-channel or theater mode, integrating well with my stereo speakers for music listening and providing earth-shaking bass thrills on film soundtracks. A single f113 was markedly better, in every way than my previous reference subwoofer, which cost nearly five times more than the f113. The JL not only had more brute-force power; it also had much greater transient fidelity, better pitch definition, and was more refined and articulate. In the subwoofer world, those qualities are usually mutually exclusive. I’ve been using JL Audio subwoofers ever since. (My colleague Jonathan Valin, who has spent his life abhorring subwoofers, became a convert after hearing JL’s flagship Gotham. He now considers a pair of those mighty subs indispensable for music listening, even with large full-range speakers.)

Ten years after launching the Fathom, JL Audio has introduced an improved “v2” version of this outstanding sub. Two models are available, the $3700 f112v2 and $4500 f113v2, the differences being driver size and output power.

What’s new in the v2 models? For starters, the power output of the integral amplifier has increased by 20% from 1500W to 1800W in the f112v, and from 2500W to 3000W in the f113v2. I never thought that the originals needed more amplifier, but that extra headroom may come in handy under extreme conditions. The driver suspension has also been redesigned for greater linearity of movement. More importantly, however, the entire audio circuit has been upgraded for a shorter signal path and lower noise. This line-level processing circuit had been mounted behind the front control panel, requiring long cable runs between the audio jacks on the rear panel and the controls on the front. Now the circuits are in the back near the input and output jacks. In addition, this audio circuitry is now housed in a cast-aluminum sub-enclosure that is bolted to the rear-panel’s massive heatsink, isolating it from noise and vibration. There’s also better isolation between the power supply and audio signal circuits. Grounding has also been modified to further lower noise.

However, the most significant improvement is the vastly more sophisticated room-correction system called Digital Automatic Room Optimization (DARO) built into the updated v2 models. This new system is an evolution of JL Audio’s Automatic Room Optimization (ARO) circuit first used in the original Fathom. In the earlier model, ARO measured the subwoofer’s in-room response (with a supplied calibration microphone) and employed a single digitally controlled analog filter to flatten that response at the listening position. Although ARO removed bass bloat and increased definition, its single filter could only reduce the room’s highest response peak. By contrast, the new Digital Automatic Room Optimization in the Fathom v2 employs 18 one-sixth-octave digital filters. DARO provides significantly more precise attenuation of bass peaks, and at more frequencies, removing those peaks with extreme precision. Note that DARO doesn’t try to equalize out dips in the frequency response by boosting response at certain frequencies; it simply attenuates the peaks. The difference between a single band of analog filtering and 18 one-sixth-octave DSP filters is night and day.

In addition, calibrating the Fathom v2 is much faster and easier than it was in the original model. In the first Fathom, you had to juggle the test-signal level during the calibration to get just the right conditions needed by ARO. But DARO is truly a “one-button” operation; the subwoofer output level and microphone gain are adjusted automatically. In addition, the stimulus signal generated by the woofer during calibration is less susceptible to extraneous noise from things like air conditioners. Where ARO calibration would require several tries, accompanied by adjustments between each attempt, DARO works perfectly the first time.

One of the original Fathom’s many virtues was the comprehensive and well-thought-out front-panel controls. That hasn’t changed in the new models, which are functionally identical. A polarity switch and a continuously variable phase control work in tandem to time-align the subwoofer’s output with your main speakers (see sidebar). All subwoofers should have both these controls (realizing correct time alignment with just a 0°/180° polarity switch is a crapshoot). Similarly, the Fathom doesn’t just give you a continuously variable crossover frequency (30Hz–120Hz), it also provides adjustable crossover slopes (12dB or 24dB per octave). Again, the extra degree of control allows the subwoofer to better integrate and blend with your main speakers. The low-pass filter can be turned off if you are feeding the Fathom with the LFE output from a home-theater controller or receiver, or if you are using an outboard active crossover such as JL Audio’s CR-1.

Yet another thoughtful and useful adjustment is the “ELF Trim.” If you’ve spent any time struggling to set up a subwoofer, you’ve probably encountered the common condition of too much very low bass. The subwoofer simply overdrives the room at very low frequencies. The excessive output adds an annoying and amusical thump that makes the subwoofer stand out like a sore thumb rather than disappear. The Fathom’s Extreme Low Frequency (ELF) Trim control lets you cut or boost (–12dB to +3dB) at 24Hz to remove the thump.

Finally, the control panel’s center is dominated by the level control knob. If you are setting the subwoofer level with a home-theater controller or AVR, the Fathom’s level control can be bypassed via a switch.