Exceeded my expectations. Clean powerful base!

Excellent product! Tight and powerful bass.

Fantastic, tight bass. Highly recommended. Great value.

i'm literally impressed everytime i power the system and hear this sub. it's paired with a monolith 15 (it's predecessor of sorts,technically), which is an amazing performer itself

Absolutely monster of a subwoofer! Bought 2 and couldn't be happier!

In short, this thing is thunderous. I've got a 20x20x10 theater room and was trying to decide between this or two of the other "well known" brand subs. After watching dozens of hours of reviews I went with this and couldn't be happier. It's MASSIVE. Sound quality is huge to match. Weighs over 150 pounds and has no problem filling my room with bass that you can feel. Honestly the most bass I've heard outside of a movie theater.

My experience with the product has been positive.
Positives:
* Easy to order on line.
* Plenty of reviews I could read and view, particularly the Youtube reviews by audio pros.
* Freight shipping by Fedex was problem-free.
* Used an unboxing video by another purchaser to guide me. Made unboxing very easy.
* Unit was very well packed to minimize probability of damage. Mine arrived in great condition.
* Setup of subwoofer was easy using the speaker calibration built into my Denon AVR-S940H receiver. I connected the RCA sub out on the receiver to a Y splitter, then into both RCA inputs on the sub.
* Sound quality is everything I expected: powerful, effortless, appropriate. In a word, accurate.
* Build quality appears to be very good.
* Unit is attractive, does not draw undue attention to itself, especially with the grill cover on.
* Love the magnetic grill cover attachment. It scared my wife with its firm grab.
Negatives:
* Can't find a link to the subwoofer manual on the Monoprice site, and none included in the box. But I found a link to the prior generation of THX Monolith subs, and that answered all my questions.
* Feet are small and short. Fingers can be pinched since there isn't much clearance. I added my own larger feet that have plastic furniture glides on the bottom. Makes positioning on carpet very easy.
Other Comments:
* Unit is very heavy. Use Egyptian boulder moving techniques (rolling rather than lifting) to preserve your body.
* Price seems high, but only on an absolute basis. Since high quality subs are not a mass market thing, supply and demand dictates a price that this unit probably does not exceed. If you really value good movie/music sound, then the price is worth it.
* For long term reliability, I probably will never push the sub to its limits, so I think the driver will hold up well over time. It appears to be really well designed. Less certain is the amp and other electronics. If they go out prematurely, then it's a hassle to send the unit back. Hope that doesn't happen. I kept the box and packing materials just in case.
Final Analysis: so far, I'm a happy customer. My hat is off to the engineers and assembly folks responsible.

The review on this subwoofer can be summed up in three words:
Absolute
Effortless
Depth
I've been in consumer electronics retail for over 20 years (was a Store Manager with Circuit City for almost 10) and am intimately familiar with some fairly awesome subs (Velodyne, HSU, REL and SVS just to name a few) but when it came to selecting the foundation of my Home Theater their ended up being only one choice.
The Monolith line, and this THX Ultra model in particular have earned a reputation for truly unequaled performance at this price point.
I have it dual calibrated, first through my Denon AVR-988s Audessy 32 EQ then really dialed in using my Avia calibration DVD and an SPL meter.
The results are simply spectacular.
During the "introduction" of the Batmobile scene in The Batman my media room vibrates with each throttle punch and in Kong vs Godzilla every footstep can be FELT not just heard.
This is a truly reference level subwoofer and I am thrilled to be its owner.

Absolutely incredible bass. Love them. Turned my theater room experience to another dimension.

I purchased mine from Monoprice on E-bay because they cheaper at that time. I am 70yrs. old so I had to handle this 150 lbs. beast
carefully. I have never heard low end that sounded so clean and
does not distort at high levels. My caution to anyone purchasing
these is to replace the feet. They mark up floor and are not heavy duty enough for 150 lbs. Sub. I purchased six SVS isolater feet.
They come with 3 different sets of screws, I used 6 MM on mine.
Floor does not vibrate now and sounds cleaner.