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Outlaw Audio Ultra-X13 Subwoofer Measurements and Analysis



The Outlaw Audio Ultra-X13 was tested using ground plane measurements with microphone at a 2 meter distance in an open setting with well over 100 feet from the nearest large structure. The sub was tested with woofer and port side facing the microphone. The subwoofer’s gain was set to maximum, phase was set to 0, and the low pass filter was left off. Weather was recorded at 70°F and 55% humidity.

FR_both_ports_open.jpg       FR_one_port_open.jpg

Frequency responses for various configurations of the Outlaw Audio Ultra-X13 

The above graphs are the baseline frequency responses for combinations of ported/sealed modes and the EQ switch. Each graph depicts how the EQ switch affects the response for that operating mode of the Ultra-X13. We can see that the EQ switch set to the EQ 2 position will grant us the flattest response, except in the sealed mode, where EQ 1 nets the flattest response in that mode. EQ 1 allows deeper extension, and in ported modes, it looks to give a bump in the deep frequencies. Those who want more low-end ‘oomph’ on movie night can flick the EQ switch to EQ 1 for more deep bass, and when they would rather have a more linear response, they can switch back to EQ 2. The flattest response of all is the THX certified mode of both ports open and EQ switch set to EQ 2. This gives an astonishingly flat response window of +/- 0.5 dB from 30 Hz to 125 Hz. Rolloff in that mode starts at 30 Hz and it is down by 6 dB at 22 Hz which is where is +/- 3 dB window would begin. With one port open and EQ switch set to EQ 1, we lose the near-perfect neutrality of the 2 port / EQ 2 response shape, but we gain a wider +/- 3dB response window of 17 Hz to 170 Hz.

Users in small rooms who see a lot of low-end room gain might prefer the EQ 2 setting in either the sealed or 1 port open configurations, unless they like lots of deep bass, in which case 2 ports open with an EQ 1 setting should give them a tremendous excess of deep bass. The upper end response in any mode is relatively good, and the Ultra-X13 could be used with high crossover points without much problem.

                                                         Outlaw Audio Ultra-X13 CEA-2010 Burst Test Measurements


 2 Ports Open, EQ 2

                                                   1 Port Open, EQ 1

                              Sealed, EQ 1

Frequency (Hz) SPL (dB) THD + N (%) Harmonic limit SPL (dB) THD + N (%) Harmonic limit SPL (dB) THD + N (%) Harmonic limit
10 - -   - -   74.5 10.2 9th
12.5 - -   96.9 12.4 5th 87.7 11.8 5th, 9th
16 98.1 22.9 9th 102.3 16.6 6th 95.8 18.0 5th
20 106.8 11.1   105.8 16.1   100.9 18.1 5th
25 111.1 9.9   108.9 9.2   103.3 11.8 6th
31.5 114.1 4.0   111.7 5.5   109.5 9.5  
40 115.2 4.4   113.1 4.3   111.4 4.4  
50 115.0 4.4   113.7 6.2   112.5 6.0  
63 115.1 5.4   114.1 5.8   113.5 6.8  
80 115.1 5.3   114.3 6.9   114.0 7.4  
100 115.0 4.2   114.2 8.1   114.0 9.2  
125 114.6 5.1   113.6 9.7   113.5 14.6  


The above CEA-2010 measurements are short-term bursts that show the subwoofer’s clean peak SPL before heavy distortion sets in. Our measurements have been referenced to 2 meter RMS, which is 9 dB down from the standard requirement for the measurements to be shown at 1-meter peak. However most publically available CEA-2010 measurements are shown at 2 meter RMS, so we followed that convention.

The results produced by the Ultra-X13 are all very good, and we do see a couple of noteworthy features in this data set. One thing we see right off is that the maximum distortion levels are generally very low. For the most part, these burst tests are being amp-limited, and the driver is not being pushed into significant distortion except in very low frequencies that are generally outside that modes’ range of operation. Looking at the THX certified configuration of 2 ports open with an EQ 2 setting, we get a sense of what THX is looking for in terms of performance targets. As we see in the baseline response for the THX Ultra configuration, the response from 30 Hz and above is extremely flat, even when pushed to the highest limits in burst testing. It is still almost within the +/- 0.5 dB window that it has at nominal levels. There is very little compression that is impacting the response. What is more, distortion is extremely well controlled in this mode, hovering right around 5%. This is extraordinarily linear behavior, and ‘clean’ is the operative word for these test results, much as it is a description of the sub’s appearance.

The other configurations of the Ultra-X13 do not quite have the linearity of the THX Ultra mode, but they are still quite good. EQ 1 with one port open grants us deeper bass but at the cost of output above 20 Hz. The sealed operating mode can gain deeper bass than that, scoring a rare passing 10 Hz burst measurement, albeit at a very low SPL. 

One interesting characteristic is that the limiting harmonics are of relatively high orders. This may be due to the amplifier’s limiter clipping the shape of the signal. If it were the driver, one would expect to see the subwoofer limited by 3rd-order harmonics, but it may be that the design optimizations of the driver has also reduced the lower harmonic distortions in proportion to the higher orders.

It should be stressed here that there is a very significant difference between just barely passing a CEA-2010 burst test and passing it with flying colors like as we see here with 5% distortion percentages. There is an audible difference in the character of a burst tone as distortion begins to creep up as a percentage of the measured sound. A passing CEA-2010 measurement does not necessarily mean that sub sounded ‘clean’ for that frequency and amplitude. While distortion is generally more difficult to discern in low frequencies, CEA-2010 testing can allow almost as much as 40% harmonic distortion, and that is very easily heard. We should also keep in mind that this distortion comes at the expense of the fundamental, the ‘intended sound,’ so it does not just tag along with the intended sound, it displaces it. Subwoofers with the same passing CEA-2010 measurements are not necessarily equal in sound quality, and one should always look distortion quantities in the test if they are interested in fidelity as well as output.

   CEA_10_12.jpg     CEA_16_20.jpg
CEA_25_31.jpg     CEA_40_50.jpg
CEA_63_80.jpg     CEA_100_125.jpg

Frequency Breakdown of CEA-2010 Burst Measurements for the Outlaw Audio Ultra-X13 

The above graphs show the measured frequency spectrum of the increasing CEA-2010 burst tests. Essentially, it depicts the behavior of the subwoofer reproducing short burst tones at successively louder levels, with each test tone raised by boosting the input gain by 1 dB until no more output was to be had from the subwoofer. The frequency marked above the graphs note the fundamental tone being tested, and this can also usually (but not always) be discerned in the graphs by the horizontal axis frequency point of the “main ridge,” the highest levels on the vertical axis. The noise below the fundamental (that random spikiness to the left of the main ridge) should be ignored. What should be looked at are the smaller ridges to the right of the fundamental; these are the distortion products of the fundamental, and it is here where we see how cleanly the subwoofer handles a given output level. These are mostly harmonics: whole number multiples of the fundamental.

These measurements were done with the Ultra-X13 in its THX Ultra certified configuration of 2 ports open on the EQ 2 setting. We do see significant amounts of distortion in the frequencies below this mode’s range of operation of 20 Hz, and that is expected, since the driver and port are at odds with each other in those frequencies instead of working together. Above that point, distortion drops dramatically, and at 25 Hz and above, the most severe harmonics stay well over 20 dB lower than the fundamental at the worst. That means they will not even be close to 10% total harmonic distortion, and this is what we saw in the CEA-2010 table, where total harmonic distortion hovered around 5% for this range. This level of distortion would essentially be inaudible. The story here is that at 25 Hz and above, the Ultra-X13, in its THX Ultra mode, can not be pushed into making an audible sound that does not belong. This subwoofer is a highly-controlled system.

Those who want to know how distortion can affect low-frequency sound can read this Audioholics article: The Audibility of Distortion in Bass Frequencies.

  Long_term_sweeps_2_ports_open.jpg     Long_term_sweeps_1_port_open.jpg


Long term output sweeps of the Outlaw Audio Ultra-X13 in different operating modes

Testing for long-term output compression was done by first conducting a 20 second sweep tone where 50 Hz hit 90 dB with the subwoofer 2 m from the microphone. We then conduct further 20 second sweeps by raising the gain by 5 dB until no more output could be rung out of the subwoofer. In these tests, we can see that unlike the burst tests, the shape of the response of the THX Ultra mode does compress a bit on the very highest sweep. The compression is relatively light in magnitude and would not make much difference in any practical usage. As one would expect in a variable tuned subwoofer, the most headroom can be had when both ports are open and in the EQ setting most suited for that operating mode. Relative to its response at nominal levels, some response is lost above 60 Hz, but it mostly compresses above 90 Hz, so it is unlikely to have a meaningful effect in real world content. In contrast, when run with 1 port open on the EQ 1 setting, the upper end actually flattens out at its maximum drive level, although response below 30 Hz does get compressed. The same effect is seen in the sealed mode.

The good news from these graphs is the responses in any of the modes do not lose shape until driven to their limit. The character of sound in any program material would not substantially change throughout the majority of the Ultra-X13’s dynamic range. Furthermore, there was never a moment when the subwoofer ‘complained,’ or made any noises of mechanical distress. The driver never bottomed out nor did I hear any obvious distortion. This is significant because these tests are the toughest that are conducted for our reviews. If the Ultra-X13 could have bottomed out, it would have during this round of testing, but it didn’t. This subwoofer is very well protected against damage from high excursions.

X13_THD_2_ports_open.jpg     X13_THD_1_port_open.jpg 


Outlaw Audio Ultra-X13 Total Harmonic Distortion per operating mode and output level 

The above graphs show the corresponding total harmonic distortion to the long-term output graphs. Essentially they depict how linear the subwoofer remains for the corresponding drive level seen in the long-term sweeps. The quantity being measured is how much of the subwoofer’s output is distortion and is shown here as a percentage. As with the burst output distortion measurements, the Ultra-X13 proves to be a very linear and well-controlled subwoofer for continuous output as with short-term output. While the 1 port open, EQ 1 mode would seem to have the least distortion, at a glance, the ‘THX Ultra,’ 2 ports open, EQ 2 configuration has the least distortion in the frequency range that are much more commonly used among these operating modes, wavering from 5% to 6% THD from the low 20 Hz range to around 90 Hz at the very highest drive level. At the nominal drivel level of the 95 dB sweep, total distortion floats around 1% of the sub’s output. That is ridiculously low distortion for a subwoofer. Keep in mind that this range is the supremely flat response range seen in the baseline response. The Ultra-X13 is keeping its promise of extremely accurate sound reproduction all around, in both realms of linear and nonlinear distortions.

For those who are wondering about the spike of distortion in the sealed graph, what is happening is the driver is being pushed very hard as it goes down in frequency. To reproduce an octave lower for any frequency, the driver has to quadruple its excursion to maintain the same amount of output, and we can see here where the driver is running out of linear throw. A limiter kicks in and restrains the driver’s motion as we go a bit lower in frequency, so distortion falls back down as the driver is reined back into a more comfortable operating range.

X13_2_ports_2nd_3rd_Harmonic.jpg     X13_2_ports_4rth_5th_Harmonic.jpg

X13_1_port_2nd_3rd_Harmonic.jpg      X13_1_port_4rth_5th_Harmonic.jpg

X13_sealed_2nd_3rd_Harmonic.jpg     X13_sealed_4rth_5th_Harmonic.jpg

Component harmonics of the Outlaw Audio Ultra-X13 for each operating mode 

The above graphs depict measurements of the constituent harmonics from the long-term output sweeps and is what the total harmonic distortion measurements are composed of up to the fifth harmonic. The individual harmonics can give us a clue as to what might be the cause of some quirk or non-linearity. The Ultra-X13 bears some noteworthy features. One feature to note is the lack of fourth or fifth harmonic distortion products above 25 Hz in the ‘2 ports open’ mode. This absence of distortion carries over to higher harmonics as well. There are minute quantities present, and they do add up, but they don’t add up to much. That is all the better for the Ultra-X13, since higher-order harmonics are much more audible and objectionable than lower-order harmonics.

The bass from the Ultra-X13 is tight and does not suffer from overhang...

In the sealed operating mode, we see that the third and fifth harmonics are the chief contributors of distortion, and that the second harmonic stays at relatively low levels. This indicates that the driver has seen some significant optimization, since even-order harmonics signifies that the woofer is being inhibited by something on only one side of its travel. The small but even spread of the second harmonic out to upper frequencies look to be caused by inductance. It is kept in check relatively well considering the how much movement the coil is undergoing and how much current is pulling through it. The shorting rings are seen to be paying off here.


Outlaw Audio Ultra-X13 group delay per operating mode 

Group delay is the measurement of how much time it takes for individual frequency bands of an input signal to be produced by the speaker. It can indicate that some frequency components are developing slower than others or are taking longer to decay. It is generally thought that 1.5 sound cycles are needed for group delay to be audible at bass frequencies, although there is an argument that group delay should remain under 20 ms to be completely unnoticeable, but that is likely meant for mid and upper bass frequencies. The Ultra-X13 gives a very good showing here, as almost all delay for every mode is kept under 1 cycle except below 20 Hz where a slight excess of delay would be very difficult or impossible to discern. For deep bass, the sealed configuration fares the best, which is expected since the port output is normally delayed by a cycle. We do see the effects of a high-pass filter in the sealed configuration, but it is very mild. No group delay from the Ultra-X13 would even be close to being audible. The bass from the Ultra-X13 is tight and does not suffer from overhang, and that much is demonstrated in this chart. Again, it shows itself to be a superbly linear sub with very high sound quality.


Outlaw Audio Ultra-X13 low-pass filter effects on response

The above graph depicts the effects of the Ultra-X13’s low-pass filter, and the curves ending from left to right are filter settings of 40 Hz, 60 Hz, 80 Hz, 120 Hz, 160 Hz, and bypassed. The low-pass slope is a 4rth order, 24 dB/octave rolloff. This slope should make it easy to blend with ported speakers if the Ultra-X13 is used in setups that lack modern bass


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Recent Forum Posts:

ryanosaur posts on January 05, 2020 23:01
Id put a third in my room if I could… but something would have to give.

Might be the relationship. :oops:

But in a 8000'3 room, I think a third would be ideal, along with two full range towers tickling 20Hz. Alas, I digress.

Still happy with my Outlaw gear after 1 year!
KEW posts on January 05, 2020 16:25
MrKaffee, post: 1360528, member: 90469
I now have two of these. Bought one last year and another this year. Took advantage of their Christmas specials at $999 free shipping. All I can say is wow! One was really good but two is simply outstanding. I have both situated behind the sectional. Deep deep bass and can shake the entire room - not just the sitting area! I had one set at eq2 but found with two set at eq1 to be sonically superior. Have the pre/pro set to large fronts and to mirror low bass below 40 Hz to the subs. It’s amazing how seamless it sounds. Right now I’m in OMG mode but like many of you am in endless pursuit of nirvana.
Yeah, once you get to a pair of these (in any normal room) it becomes a real question if more would really add anything (that you want added). It is like riding a 1100cc motorcycle - there are bigger bikes, but how much more acceleration do you need when you can twist the grip and flip the bike on top of you!
MrKaffee posts on January 05, 2020 15:29
I now have two of these. Bought one last year and another this year. Took advantage of their Christmas specials at $999 free shipping. All I can say is wow! One was really good but two is simply outstanding. I have both situated behind the sectional. Deep deep bass and can shake the entire room - not just the sitting area! I had one set at eq2 but found with two set at eq1 to be sonically superior. Have the pre/pro set to large fronts and to mirror low bass below 40 Hz to the subs. It’s amazing how seamless it sounds. Right now I’m in OMG mode but like many of you am in endless pursuit of nirvana.
andyblackcat posts on August 11, 2018 20:41
Yeah cheaper ones possibly. Always liked to have one of those older M&K subs before the company changed its name? As they show up cheaply now and was around cost of above Outlaw THX sub.
shadyJ posts on August 11, 2018 17:40
andyblackcat, post: 1262768, member: 70814
Well least you know about that as I was thinking what NASA does when pressurizing the shuttles cabin then they check for leaks to see if its okay to launch. So same for speakers/subs I guess as I had to check over older speakers that had drill holes and had to seal the holes then run a loop frequency sweep checking for air leaks and resonate noises.

Still maybe a little silicon going around the plate amp as you may never know there could be one spot where its venting air?
A lot of these amps are already sealed in with glue, along side the screws, so I wouldn't worry about leaks too much with this build class of subwoofer. However, very inexpensive subs may be a different story.
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