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Monoprice Monolith 10” & 12" THX Subwoofer Review Conclusion


monolith outdoor testing

The 10” THX Select and 12” THX Ultra was tested using ground plane measurements with microphone at a 2-meter distance in an open setting with at least 200 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 81°F and 35% humidity.

10 frequency response curves     12 frequency response THX EQ Mode

12 frequency response extended EQ Mode     12 frequency resoponse EQ comparison

Frequency responses for various configurations of the Monolith THX subwoofers

The above graphs are the base 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 Monolith THX subwoofers. Any combination of EQ and port configuration yields a very flat response on these subs, with both ports open yielding the most output and one port open producing more output at deeper frequencies. Sealed mode rolls the sub off at a higher frequency but shallower slope. The rockiness in the response at the low end of the graphs for the 12” THX Ultra is not the behavior of the subwoofer itself, it is from environmental noises leaking into the microphone that were not able to be filtered; the subwoofer’s actual response is very smooth. In their ported modes, these subs all have a picture-perfect response from 30 Hz to 200 Hz with usable output all the way up to 400 Hz. Above 400 Hz they all roll off sharply. This subwoofer could easily be used with a 200 Hz crossover point if desired by the user.

The difference between the THX EQ and Extended EQ isn’t huge but it is notable, amounting to a few more dB in the low end in Extended EQ. The difference between port configurations is much more substantial, of course, exchanging output from 20 Hz to 50 Hz for extension below 20 Hz. Sealing the ports throws away a lot of deep bass output, but it might be useful in smaller rooms that incur a lot of low-frequency gain in order to avoid overly boosted deep bass.



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 publicly available CEA-2010 measurements are shown at 2-meter RMS, so we followed that convention.

...these subwoofers have near perfectly-balanced performance within their operational bandwidths.

All CEA-2010 measurements shown here were with the Monolith subwoofers used in the THX EQ mode. The subwoofers were also tested in Extended EQ mode, but the differences between the EQ modes were very slight. Extended EQ and THX EQ did not seem to make much difference in this type of testing. The measurements are all quite good for both subs. Both exhibit excellent linearity even when pushed to the edge of their performance as they are in this testing. Their response shape barely changes from nominal levels, and the distortion is mostly very low. Their behavior does not change much regardless of how hard they are being pushed in both linear and nonlinear domains.

The Monolith 10” THX Select does not have a huge amount of midbass output, and that is likely due to the heavier moving mass of the cone and voice coil, but that is a necessary trade-off towards achieving the superb deep bass performance that it produces for its size and price. Its midbass output is commensurate with its deep bass output, whereas most subs at this pricing will have substantially more midbass output than deep bass. Clean, deep bass is more difficult to pull off, and that is what is so impressive about these measurements. The 12” THX Ultra has nearly twice as much headroom across the board than the 10” THX Select, and that is not surprising given the larger driver and enclosure size. As we saw in our review of the Outlaw Audio Ultra-X13, THX Ultra certification of the 12” THX Ultra subwoofer seems to demand total harmonic distortion not be much more than 5% from 30 Hz and above. It looks like the THX Select certification may be a bit more relaxed regarding distortion based on these measurements of the 10” THX Select. It should also be said that the day of testing had a slightly higher noise floor than usual, so if anything, our THD numbers are slightly higher than normal, but we feel comfortable posting these measurements since a lower noise floor wouldn’t have changed the results by a tremendous degree.

It should be noted that the measurements for the sealed operating mode are quite good. Those who are debating whether to get a ported subwoofer or sealed subwoofer have a good example of either with these Monolith subwoofers. The tremendous linear throw of the drivers and powerful amplifier insures good performance with or without the ports. Ports do give them a hefty advantage in deep bass headroom, so that is what I would recommend for most users who purchase either sub.

10 Ported THX long term output     10 Sealed THX long term output

Monoprice Monolith 10” THX Select long-term output compression

12 1 port THX long term output     12 2 ports THX long term output
12 Sealed THX long term output

  Monoprice Monolith 12” THX Select long-term output compression

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 wrung out of the subwoofer. These tests show us the long-term continuous headroom that these subwoofers can be made to produce. First things first, the compression behavior of these subs are superb. The response shape scarcely changes from low drive levels to high drive levels. This is how you want your subwoofers to behave; there should be little difference in their amplitude response shape regardless of the volume level. Of note, look how beautifully flat the response stays with the 10” THX Select in its ported mode and the 12” THX Ultra in its 2 ported mode- recording those kind of perfect measurements makes my heart flutter. I also ran long-term sweeps of the Monolith subwoofers in the ‘Extended’ EQ setting of these modes, but the differences between the EQ settings was minor in this testing, much like the burst tests.

There is some rockiness in the very low frequencies in these graphs, but that is from gusts of wind; it was a very windy day when I tested these subs, and the microphone’s windscreen does not totally block out wind effects in these ultra-deep frequencies. These subwoofer’s actual deep frequency response is very smooth. These subs are very well behaved at all drive levels.

10 sealed THX THD     10 ported THX THD

Monoprice Monolith 10” THX Select Total Harmonic Distortion

12 1 port THX THD     12 2 port THX THD
12 sealed THX THD

Monoprice Monolith 12” THX Ultra Total Harmonic Distortion

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. Both Monolith subwoofers sport very good measurements here, but the 12” THX Ultra does better as it mostly isn’t able to exceed 5% THD for the wide majority of its bandwidth at 25 Hz and above. The 10” THX Select looks to be allowed larger percentages of distortion, as it can be pushed to around 10% THD in that same bandwidth. Comparing the 2 port open mode to the 1 port open mode on the 12” THX Ultra might make it appear as though the 1 port mode has much cleaner deep bass output, but it must be remembered that output rolls off sharply where distortion rockets up, so while using 1 port only on the 12” THX Ultra technically grants cleaner deep bass, the distortion in the 2 port configuration will not be heard since there is so little output in that region at all. It should also be remembered the frequency response and output levels for these distortion graphs: the 12” THX Ultra is running at or near 110 dB at 2 meters for this 5% THD level average. That is superbly clean bass for that output level, and this makes the 12” THX Ultra a very high-fidelity subwoofer. The 10” THX Select is up against more trying circumstances due to its smaller cone and enclosure, but it still puts up a good showing by maintaining a 5% or lower THD level until the last few dB of its headroom where THD climbs to 10%.

As with burst testing, the Extended EQ mode changed relatively little in these measurements from the THX EQ mode. The total harmonic distortion in these subs is chiefly composed of third order above the port tuning frequency and second order at and below tuning.

10 group delay     12 group delay

Monoprice Monolith subwoofers’ group delay measurements

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. Group delay for either sub is superbly controlled, not even rising above 10 ms until it is down to 40 Hz, and mostly staying below 20 ms down to 30 Hz. Below that, the frequencies are too deep for the measured delay to ever be of audible consequence. These graphs tell us that the Monolith THX subwoofers will not have any audible overhang. Owner’s will only have to worry about what the room acoustics will do to the decay of bass sound and have nothing to worry about from the subs themselves.


The Monoprice Monolith 10” THX Select and 12” THX Ultra have similarities but also some significant differences which make it difficult to summarize them together in this combined review. They look the same except for size, use many of the same parts, and have some spair angle 2imilar performance characteristics such as their frequency response behavior. However, they also have some very real differences. The 12” THX Ultra is a much more powerful subwoofer. The larger cabinet and cone size give it a very substantial advantage, but that also comes with a disadvantage; it is large and very heavy. I have encountered ported 15” subwoofers that were easier to handle. You have to be careful when lifting 12" THX Ultra model and setting it down as well, because the “feet” are so small that they don’t even give your fingers enough clearance between the sub and the floor. In contrast, the 10” THX Select is much easier to move around. I can lift the 10” THX Select without any assistance, but I wouldn’t dare try that with the 12” THX Ultra. Some readers might be thinking that subwoofers are just something you set in a corner and forget about it, so physical manageability isn’t a big advantage, but if you want to get the most out of your subs, you'll need to find the best locations for them in room, and that means moving them around. Since finding proper placement is such a crucial aspect of acquiring good bass sound, transportability should be seen as a performance advantage, and it’s easier to optimize a system using 10” THX Selects than it is using 12” THX Ultras.

So, we have one subwoofer that has a reasonable size and weight and offers good performance for the price, and we have another sub that is a beast, both in physical attributes and performance attributes. One important commonality is the sound performance of each sub is definitely above average for the price points. As seen in the measurements and analysis, these subwoofers have near perfectly-balanced performance within their operational bandwidths. THX certification mostly concentrates on 25 Hz and above, and in that region, these subwoofers are exceptional; there is virtually no deformation of the amplitude response no matter the drive levels, and there is no audible distortion no matter the drive level. Both these subs have enough output to meet Audioholic’s Bassaholic ‘Large’ room rating, with the 10” THX Select just squeaking by to capture that rating and the 12” THX Ultra very comfortably meeting that room rating. The Bassaholic ‘large’ room rating means that these subs should be suitable for a room in size from 3,000 cubic feet to 5,000 cubic feet. While the 10” THX Select does technically qualify for that rating, I think it would get overwhelmed in a 5,000 cubic foot room. I wouldn’t advise using it in a room much larger than 3,000 cubic feet.

Bassaholics Large room rating

Just from glancing at them, they might look like bruisers that are geared for low-frequency effects for movies, but their superb accuracy makes them ideal for dedicated music systems as well. There may be other subs around the same pricing that can produce more SPL, but few can achieve the loudness levels that these do with near picture-perfect behavior. Indeed, in our brutal testing, their sophisticated digital processing restrimonolith woofer insigniacted them from going into ranges of excursion that would have placed the drivers in harm. These subs are bulletproof, so users don’t need to worry about over-driving them; they can’t be over-driven.

But Are They Pretty?

Regarding their appearance, the Monolith THX subwoofers may not be the prettiest subwoofers around, but they do not look bad, and I am sure many folks would even dig their muscular look. Their build quality is extraordinarily good for these price points. Cabinet construction, driver build, and amplifier quality are of a level that one would expect to see in considerably more expensive subwoofers. What is more, shipping is free for American buyers in the contiguous USA. The Monolith subs also come backed by a full 5-year warranty (non-transferable), raising their value proposition even further. Buyers also get a 30-day trial in which they can return the subwoofers for a full refund if they are not happy with them for any reason.

Given everything that can be seen here, Monoprice has entered the fiercely competitive subwoofer market with full intention of becoming a major player. They have ensured that they will be mentioned in the same breath as the established high-value, heavy-duty subwoofer brands. Anyone who is considering adding bass to their system would do well to take a close look at these subwoofers for the $500 and $800 price points. My time with the Monolith THX subwoofers has shown them to be well-engineered and well-executed products that audio enthusiasts will be fortunate to have as a stand-out option to choose from in this crowded field.

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
Bass ExtensionStarStarStarStarStar
Bass AccuracyStarStarStarStarStar
Build QualityStarStarStarStarStar
Fit and FinishStarStarStar
Ergonomics & UsabilityStarStarStar
Dynamic RangeStarStarStarStar
Attached Files
About the author:

James Larson is Audioholics' primary loudspeaker and subwoofer reviewer on account of his deep knowledge of loudspeaker functioning and performance and also his overall enthusiasm toward moving the state of audio science forward.

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Recent Forum Posts:

Luky.Kluk posts on November 24, 2021 07:17
FYI Black Friday sales began today on Monoprice.eu
shadyJ posts on March 11, 2021 14:32
Prolix, post: 1467570, member: 95128
I'm considering getting dual Monolith 10s vs a single PB-2000 Pro. With the Monoliths I'm concerned about the relatively high distortion through the midbass (is it audible?) and the relatively low peak midbass output. With the SVS I'm concerned about the high group delay and missing out on dual subs. Basement cave is 12x20x7 and I usually find reference level far too loud so am thinking with the dual monoliths I'll rarely push into the high distortion zone. Thoughts? Other options?
Your concerns about group delay and distortion are unwarranted. Neither are at levels that are audible. Between those two choices, I would go for the Monolith subs because multiple subs can yield a flatter response which means better sound quality - but only if you take the time to set them up correctly.
Prolix posts on March 11, 2021 12:47
I'm considering getting dual Monolith 10s vs a single PB-2000 Pro. With the Monoliths I'm concerned about the relatively high distortion through the midbass (is it audible?) and the relatively low peak midbass output. With the SVS I'm concerned about the high group delay and missing out on dual subs. Basement cave is 12x20x7 and I usually find reference level far too loud so am thinking with the dual monoliths I'll rarely push into the high distortion zone. Thoughts? Other options?
FlyingBoat posts on April 29, 2019 16:08
Its for $675 because through the 29th there is a $125 off $500 monoprice coupon code that this works on.
1BADAPPLE posts on April 27, 2019 18:15
Thanks WCG.
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