Monoprice Monolith 12" and 15" THX Ultra Subwoofers Review

Monolith 15"
Build Quality

Monolith 12"
Build Quality
PRICE $800, $1,300

Clean, copious, and articulate bass
Outstanding build quality
Five-year replacement warranty
No parametric equalizer
No app control
Extremely heavy

Entry into the crowded internet-direct subwoofer market is a bold move from Monoprice, but the performance of these subs will surely make some waves and breed some fierce competition.

Reproducing a movie soundtrack in a home environment isn’t an easy task. At your local cinema, the theater will hopefully have sound dampening so you don’t hear outside noise. And if you’re lucky, the system will be calibrated properly and provide enough headroom so there’s no clipping or distortion during the dynamic portions of the soundtrack.

In most homes, you have to contend with a lot of extraneous factors. The acoustics may not be right, with the room being too bright (not just sound-wise but also light-wise) or too dead (making for lifeless audio). This can affect your enjoyment of the movie. Furthermore, the quality of your gear matters. Sure, a 32-inch budget TV and soundbar from the local big-box retailer may be fine for watching the news, but do you get the visceral impact that’s required when Luke blows up the Death Star?


While every component plays its part in the presentation, the subwoofer is arguably the one that can make the most noticeable improvement to a budget home theater system. When I have visitors over, they often marvel at the size of the screen (though, at 88 inches diagonal, it’s still pretty modest by serious home theater standards). If I pop in a Dolby Atmos demo, they’re amazed by the sound coming at them from every direction. But I get the biggest reaction, by far, when a bottom-heavy scene comes up: “I can’t believe how much I felt the bass,” they’ll usually say. “The entire floor was vibrating!”

Editor-in-Chief Rob Sabin calls me the resident basshead at Sound & Vision, and that’s a badge I wear with honor. My reference system includes four subwoofers: an SVS PC-Ultra, a Hsu Research VTF-15H MK2, and dual JL Audio Fathom f110 cabinets, all calibrated using the freeware program REW and a miniDSP to get the subs to play nice with each other. It took me days of calibrating to get the quartet just right, but if you care about bass like I do, it’s time well spent.


New Kid on the Block
Being the basshead of S&V gives me certain perks—among them, the opportunity to sample a lot of subwoofers and be one of the first to do so. Enter Monoprice, best known for cables that deliver high-quality picture and sound at prices the masses can afford. As time has gone on, the California-based company has started to expand into self-branded components—such as Monolith amplifiers, one of which I reviewed quite favorably in 2016, and now Monolith THX-certified subwoofers.

These new subs come in three different sizes: the 10” THX Select and the 12” and 15” THX Ultra. The latter two are the subject of this review. The conception of THX goes all the way back to 1982 and was the brainchild of George Lucas, who was not pleased with the way theaters were showing his films. He hired audio scientist Tomlinson Holman, who set up a rigorous program that started at the production studio before reaching theaters and, eventually, home components. THX certification comes in four flavors: Compact, Select, Ultra, and Dominus. THX Select applies to rooms up to 2,000 cubic feet, and THX Ultra is for rooms up to 3,000 cubic feet. To attain Ultra certification, subwoofers (and other speakers) must undergo myriad tests—for sensitivity, frequency response, distortion, etc.—and be able to play at 85 decibels and have +20 dB of headroom at the specified listening distance. The takeaway is that THX Ultra subs must have low distortion and the ability to play down to at least 20 hertz.


The internet-direct subwoofer market is extremely crowded, especially in the realm below $1,500. The Monolith 15” sub checks in at $1,300, with the 12” version at a relatively budget-friendly $800. Currently, shipping is included with these prices, which makes them very competitive.

Specs-wise, both subs check all the right boxes. The 12” has two ports and sports a 500-watt Class D amplifier built around a Texas Instruments 48-bit data path (with 28-bit filter coefficients) and DSP engine. The 15” has three ports and is powered by a 1,000-watt Class D amp built around the same Texas Instruments DSP engine. The use of ported designs allows both models to have substantial SPL capabilities, and port plugs let you customize the character and extension to fit your particular room and tastes.

Not Your Typical Black Box
Generally speaking, subwoofers won’t be entered to win any beauty contests, but these Monolith subs are quite attractive. For each, Monoprice has chosen to use chamfered corners that provide an octagonal shape to the front face versus a boring square box. The woofer, embossed with a Monolith logo, can be covered using the removable grille, which is floated slightly away from the baffle. The cabinet itself is built with HDF (high-density fiberboard), which adds to the weight significantly, but this does help the sub maintain a sonically inert structure.

Each driver has been customized for Monoprice and appears to be well constructed to provide extreme cone movement. The 12inch woofer is specified to be capable of more than 80mm peak-to-peak mechanical excursion; the 15-inch woofer expands this to more than 90mm. To put that in perspective for the U.S. audience, that’s 3.15 and 3.54 inches of front to back cone movement, respectively.

drny's picture

Daniel I'm sure the Monoprice subs are quite good.
But what I really NEEEED to know is how did you persuade your wife (if your married that is) on the four reference Subs you already own.
I have a Deftech STS Home Theater speaker system with an additional 10"Deftech supercube sub.
My speaker selection was highly influence by their aesthetics as my wife nixed much larger Home theater speaker systems that I preffer(ugly, says my beloved).
I have attempted to add the same HSU Research and SVS model subs you owned, but no dice.
You will be my eternal God if you so kindly share your enchanting the wife skills.
Mine stink. Adding a ceiling projector and retractable screen cost me a complete kitchen remodel.
If you are single (co-habitating does not count, as they can't leave you broke on the gutter) disregard my request.

David Vaughn's picture
Patience is a virtue :) It took me years of convincing, but it helps that I earn income from this writing gig and I pulled it off as "it's something I HAVE to do!" By the way, you made me LOL with the kitchen remodel because that's how I got a front projector in 2005!
jalan's picture

For $300 more wouldn't a setup of dual Monolith 12's be far superior to the single Monolith 15? Both seem like well made and fantastic subwoofers but The 15 at $1000 or $1100 would be a more logical price point.

David Vaughn's picture
Yes, dual 12" subs would be the preferred setup if you can't swing the cost on the 15" subs. While you'll give a little up in deep bass extension, that's something you feel rather than hear anyway. If I were on a budget, that would be the direction I'd go.
hk2000's picture

I have a 10" Velodyne that goes down to 19Hz, like the Monolith 12, and I do feel the bass, the floor shaking under my feet from 10 feet away, so why would the Monolith not be able to do that.

David Vaughn's picture
It can, but the Monolith 15 goes deeper than the 12.
hk2000's picture

Those subs are way too heavy, how are you supposed to experiment with location? That'd be a killer chore.
Also, why use 4 different Subwoofers? Most reviewers always advocate same make and model, and you turn around and mix and match from 3 different manufacturers? And one more thing, who listens at home at THX levels? unless you have no neighbors, of course.

David Vaughn's picture
I used furniture sliders to move them around. As for multiple subs, you can mix an match, but it makes integrating them harder. That's why I use a Mini-DSP, which allows me to integrate the 4 subs as one. This takes a lot of time to do right, which most people aren't willing to do, which is why using the same sub manufacturer the "easier" choice.
David Vaughn's picture
As for THX levels, I don't listen that loud unless I'm testing products to ensure they sound proper at those levels (generally, it's much too loud for me). The loudest I personally like to go is -10 from reference, which is plenty loud.
hk2000's picture

So, if I'm more interested in extension- especially at lower volume than I'm in maximum loudness, wouldn't it make more sense to go for a sub that may be limited in headroom , but accurate to below 20hz?
I'm currently using 2 subs in my theater room that can dig down to below 20hz (at reasonable loudness)and still give me enough visceral impact that I more feel than hear, and yet, even put together, they weigh less than either of these monoliths here.
Frankly, I feel Monolith is trying to be the American muscle car in the lot of exotic imports, offers a lot of value /performance, but leaves something to be desired. But I'm sure they'll generate a lot of interest for the value they offer.

David Vaughn's picture
They weigh so much because of using HDF, which is much heavier than MDF or plywood. I'm not sure what benefit, if any, the HDF offers, but definitely does add to the weight of the subs. The good news is once they are placed in the proper spot (or spots), you never need to move them again until the next upgrade comes along :)
kevon27's picture

Please have Monoprice send you the 10 inch sub for review. That sub will most likely be the preferred choice for people with apartments and small rooms.

David Vaughn's picture
Check over at AVS and you'll see some people that have bought it and like it. Given the performance of the 12" and 15", I'd almost blind buy it if you have space or noise constraints.
DoughMucker's picture

I've had a Mirage Omni S8 for several years and though it has nice sound, it doesn't have enough oomph for my medium sized basement theater. So, after reading this review, I think it's time I pull the trigger on a couple of these. My room is about 2700 cubic feet (11.5'x31'x7.5'). From what I've read, the 10" version would be too small, but would two be enough to pressurize the room? Or do I really need to step up to the 12" subwoofers?

David Vaughn's picture
The 12" will go deeper, especially two of them.
DoughMucker's picture

Thanks. I had already went ahead and bought two of them. :) Arriving in a few days.

David Vaughn's picture
That's great to hear. Be sure to post any thoughts you have on them.
Adam Wade's picture

I have a 5000 cubic foot apartment/living room. I want a sub mainly for movies -- for that deep bass impact.

Until now I was targeting the subs from HSU, SVS, and Rythmik for this price point. Not sure where these Monoprice fit into that segment.

David Vaughn's picture
These fit into that segment, although if size isn't an issue, the HSU VTF-MK2 at $859 is a much better value. I use one of these as my reference subs and it does an outstanding job.
jpgin's picture

What happened to the Marantz 8802a?

mmamun7's picture

Total home is approximate 2,000 sqft. Will setup in loft (upper floor), 20ft by 17ft. One side of loft is open to lower floor living, kitchen dining. I am confused among SVS PB or SB 2000 (500 RMS)/ Monolith 12"(500 RMS)/ HSU VTF-2 MK5 (350 RMS) subwoofer. Which subwoofer should I get?
Movies 65%, Music 35%

Have Martin Logan Motion 40s as main speaker.
Any help?

Film235's picture

Hi Dave, I’m building an M&K atmos system at home (S150s & SS150s) and I’d like to upgrade my sub from a VX-760. Is a MX-350 the way to go or is the Monolith 12 a better option? I believe you’re an old M&K guy like me, so I thought I’d ask your advice. Love your work, thanks!