Subwoofers

JL Audio Fathom f112 Subwoofer

ARTICLE INDEX

Front panel controls include

• A power switch - This can be set to Off, On, or Auto. I don't use Auto, on any subwoofer. Subwoofers only get sent, by virtue of their job description, the lowest frequencies. As a result, they won't wake up until some significant amount of bass makes it into the soundtrack. During the time of that transition between Standby to On, they don't reproduce that low bass. A good implementation will minimize the turn on delay, and not turn off before you're done listening to whatever. The JL Audio implementation is thoughtful, with a 30 minute turn off period (after 30 minutes without audio to the subwoofer, the unit will turn off), and Carl's blog site goes into ways to optimize the operation of auto-turn-on systems. But, I don't think the mild energy savings really makes this feature worth much, and as Carl points out, many electronics actually last longer if you simply avoid power cycling and leave them on. But it's there if you want it. I set the switch to On, and just left it there.

• Automatic Room Optimization - When used with the supplied microphone (plugged into the microphone input), these controls allow you to set up the room correction system, which applies EQ to compensate for response anomalies relating to the interaction of the subwoofer location and the room itself. This isn't as comprehensive as some of the room correction systems that make measurements at multiple locations, and then applies a weighted curve, but it can really be handy if you've got a nasty peak that distracts from the musical or theatrical content, long after the novelty of the 'ultra shake' at that frequency wears off. There's an input for a calibrated microphone, a Demo button (which would seem useless to the end user), a Defeat button, which lets you bypass the correction, and a Calibrate button, which lets you start the whole procedure.

In reference to the Demo button though, here is what Carl Kennedy, of JL Audio, had to say: "The demo button serves many valuable purposes. For the installer it can be helpful to test-position the sub in various locations while using the demo button to listen for octave-to-octave performance "in room" without setting up a source. It is a good place to start when trying to figure out why your sub may not be playing allowing you to rule in or out a dead sub and direct your attention efficiently toward wiring or settings. It is a good way to confirm that master/slave is set and wired correctly prior to having a preamp and player connected. Lastly and most importantly it is a priceless tool when discussing tech issues over the phone. By talking the installer or consumer through a variety of settings on the phone we can both evaluate and troubleshoot a sub's operation and even educate a consumer on what they are hearing using these specific tones."

I need to applaud the implementation of the Automatic into the ARO. The Infinity Beta 10" subwoofers I had previously reviewed some time back also had a room correction notch filter, but the automated calibration process was far easier with the JL audio. Set up the microphone, press the button, and it emits a series of tones first to allow you to set a level loud enough to really get a good signal to noise ratio, but not so loud as to overload the subwoofer into distortion. Once it's satisfied that we've set the volume via the master level to correct levels for the test, it does a slow sweep over its operating range, applies a correction filter, and it's done. It really is very easy. No playing tones and plotting the response and then adjusting a variation of a slide ruler to derive settings. Bypass the subwoofer controls, press one button, maybe apply a couple knob turns to set the test level, reset the controls, and fine tune the settings. The actual correction process is done within minutes. In the case of multiple subwoofers, you can either do a correction for each subwoofer individually (for instance, if you're running them in stereo), or you can connect one subwoofer through the 'master', using a cable from the master's output to a special input, and have a single filter applied to the summed subwoofer response.

After getting both subs in good room positions, that needed no obvious correction across a wide listening area, between correcting the room response of each subwoofer at a single location and simply defeating the correction, I preferred not using the room optimization. It did sound tighter, but also had a little less body. I wondered at first if a flat response just lacked the peaks that add a superficial punch, but compared to headphone listening, there was a bit missing. I suspect that my particular room acoustics, which simply do not work, at all, with a single subwoofer location, anywhere, may have something to do with individual correction not carrying the day. I will try out the latter method, using a master and slave setup, where one microphone and filter compensate for the summed response of both subwoofers, and report results as I have them. Regardless, it's a cool, easy feature that will most often come in handy, and if it doesn't, you don't have to leave it engaged. One thing that did bug me, though was that if the subwoofer loses power, upon power up, it turns off the Defeat option. I'd prefer that it remembers my last settings. Minor thing.

• Master/Slave indicator - This simply indicates whether the subwoofer is configured as a master (who dictates how the signal is driven through level/crossover/correction adjustments) or a slave (who takes the signal as dictated by the master). You actually set this on the back of the subwoofer, but if you're trouble-shooting, it's nice to know on the front panel, and you simply get another set of cool LED lights.

• Volume control - There is both a Ref/Variable switch, that lets you set the gain to a fixed level with Ref, or a variable level with Variable, as well as a knob that allows the user to adjust that variable again with the Master Level.

• Light control - No, not the room lights, smarty pants. Front LED display brightness. There's High, Low, and Off, to suit most any occasion.

• Low pass filter slope control - Options are Off, (used if you've got an outboard crossover, or your preamplifier is performing that function) 12 dB, and 24 dB (per octave).

• Low pass filter frequency control - Allows setting the cutoff point for rejecting higher frequencies from 30 Hz to 130 Hz.

• E.L.F. trim, -12 dB to +3 dB - This is essentially an adjustable EQ for the very lowest frequencies, primarily to allow a user to adjust the very bottom of the subwoofer response to compliment the amount of room gain, most often so that you won't have to put up with the infrasonic exaggeration resulting from subwoofers with very deep bass response put into rooms that emphasize the same.

• Variable phase control from 0-280 degrees - Used to match the phase of the subwoofer to the main speaker(s) it compliments. The most direct way of setting this is to play a tone at the crossover point, and adjust phase until it's loudest, at which point the waveforms will be in phase.

• Polarity switch - 0 or 180 degrees, often otherwise labeled as Positive and Negative Polarity.

Altogether we've got all the basics on the front panel for fine tuning the response of the subwoofer(s). Many users will never touch these controls, but rather perform the respective functions in their preamplifier/controller units, but it's really handy do have them, and darn it, those knobs are just plain pretty, and options are always good!

A quick look at the Fathom f112's rear shows sheer, elegant, utility. The back plate itself is a heat sink, with a sparse collection of connections and a couple switches.

There are two pairs of audio inputs, both XLR balanced and RCA unbalanced. The RCA unbalanced inputs happen to be opto-isolated (isolated via an optical conversion, to eliminate the possibility of ground loop). There is also an XLR output to other Slave subwoofers, and a switch that designated the operation of the subwoofer as either a Master or Slave (we'll get into this later). In addition to a switch that allows you to either ground or float the audio ground in relation to the power ground (one more tool to fight potential hum), there's an IEC power socket.