Measurements & Analysis

I moved the f110s outdoors to conduct some 1 meter groundplane measurements. I tested extension vs SPL by varying the input drive until I heard any audible distortion emanating from the sub.

 

Fathom f110 (left graph); Axiom EP400 (right graph)

1 meter Groundplane measurement (no smoothing)

The output was very clean for the “low2”, “mid2” and “high2” traces with a slight hint of audible woofer strain below 30Hz for the “high2” trace. I didn’t detect any cabinet noise or leaks during my testing. I bumped the input level up a bit more for the “max” trace to see how much usable output I could achieve and found the f110 remained very clean until it swept below 30Hz. At that point the woofer was simply trying to play beyond its excursion limits. -3dB point appeared to be around 25Hz with a fairly steep (but expected for a sealed design) roll off of about 25dB per octave below that. Many DSP controlled subs tend to inject a brickwall filter right below the -3dB point such as the Axiom EP400. While this is certainly a valid design approach, especially for small drivers, I prefer the more gradual roll off that JL Audio employed on their f110. In my opinion it’s important to not simply discard low frequency bass info as a natural roll off below the -3dB point tends to improve tactile response. Inserting a brickwall HPF can result in negative temporal consequences of the signal in the range where our hearing is most sensitive to phase.

For comparative purposes, I pulled some measurements under the same test conditions for my Axiom EP400s. As you can see in the graphs, the f110 has considerably more output than the Axiom EP400 (+6dB more below 30Hz and between 10-14dB in the 40-80Hz range), but the EP400 exhibits flatter response above 30Hz than the f110 all the way out to 120Hz. Considering that the f110 has a bigger driver (10” vs 8”), larger enclosure, and is nearly double the price, it speaks volumes for just how good the little EP400 really is.

I found it a bit puzzling that the f110 exhibited around -5dB of rolloff at 100Hz despite I had the LPF on the subwoofer disabled. This was especially vexing since the f112 measured flat to 100Hz in our testing which utilizes a larger driver. This measurement anomaly seemed to contradict the JL Audio -3dB at 120Hz published specification. Above 80Hz the f110 exhibited an 18dB/octave rolloff. When I questioned JL Audio engineering on this they said it was deliberate as the sub simply sounds better and plays cleaner by introducing this roll off. Using a high mass driver (with a large, high inductive voice coil) like the W7 JL Audio employed here, its understandable why. I personally feel the part of the reason why some subwoofers tend to sound “faster” is related to its output above 80Hz and how it preserves the harmonic content of the bass frequencies. Because of this issue, I deducted ½ point from my final performance rating for this product. It is a good idea to experiment with the crossover in your A/V receiver / processor by setting it higher than 80Hz and/or possibly defeating it, especially when placing two f110s as a stereo pair configuration near your front main channels like JL Audio recommends.

Editorial Note on f110 Bandwidth from Brett Hanes (JL Audio Senior Research Engineer)

While the baseline response above 80 Hz is somewhat rolled off compared to other subs you’ve tested, the ARO Calibration will significantly alter this condition. To elaborate on this point, listeners usually set the sub level according to its mid-band response (50-70 Hz). When this level gets pulled down by the ARO due to room-mode involvement (pretty common), the subsequent automatic level compensation will adjust for a similar mid-band level as before. Since the mid-band was cut by the system, this will bring up the "tails," effectively extending the sub's bandwidth. This can be seen in your own "with and without" ARO plots in the review and is always quite evident when you measure the subs by themselves after Calibration.

Our survey of dealers, installers and end-users indicates that the vast majority use our ARO feature, and they feel it improves performance dramatically. Calibration results in a substantial modification of the baseline response and produces an effective bandwidth extension. As a result, this can enhance the usability of the F110s with smallish satellite speaker systems. They will perform very well together in most room circumstances.

Since I don’t yet have the ability to accurately measure distortion vs SPL on my test gear, I asked JL Audio to provide me their data which is tabulated below. Also attached via a PDF file is their SPL vs distortion data plotted in MATLAB.

Max SPL vs Distortion Tests

Tested by Brett Hanes & Eric Krumme

The 1 meter ground plane signal amplitude is equivalent to a 1 meter, half space (2pi) test.

If you look at their data at 25Hz, you will see they measured 101dB max SPL and about 94dB at 10% THD which coincides closely with my “max2” and “med2” SPL plots, respectively. At higher SPL levels below 30Hz is where I started to hear woofer straining mostly because the W7 woofer reached its excursion limits. 10% THD is an industry standard threshold for measuring subwoofer distortion. While this limit can be audible with continuous sine wave sweeps, it is likely not audible with real program material. Above 25Hz, JL Audio reports much higher SPL #s than I measured. The reason for this is my sweeps were conducted at a constant input level across the entire bandwidth whereas JL Audio conducted discrete max SPL tests per frequency tested by varying the input level until they measured 10% distortion. This is a much more accurate way of testing max SPL as the frequency sweep tests I conducted are limited to the subwoofers low end output capability which rolls off drastically on the f110 below 30Hz. In the future I will add this test methodology to my reviews once my Audio Precision APx585 analyzer is upgraded to measure loudspeaker distortion.

Noise Leakage Test

When I ran low frequency sweeps from 300Hz down to 20Hz up to levels causing the f110 woofer to reach its excursion limits. At all power levels, I didn’t detect and leakage noise or cabinet rattling which is a tribute to how well put together this product is.

f110 with (green) and without (purple) E.L.F. boost

The f110 has an adjustable boost (+3dB) /cut (-12dB) feature centered at 28Hz which they refer to as E.L.F.(Extreme Low Frequency trim,; not to be confused with subwoofer manufacturer Bag End whom uses a similar name for their version and to my knowledge was the first to call it such). As you can see in the graph, with an ELF boost of +2dB the entire output did go with, especially below 28Hz as claimed by JL Audio. This is a useful feature to tame bass modes which are a common occurrence in that frequency range, especially when sitting near a back wall. It’s also equally useful for giving your low end a little boost if needed especially when dealing with anemically bass challenged music content or fighting non ideal subwoofer placement in your theater room.