Monolith by Monoprice 13-Inch THX Ultra Certified Subwoofer Review Page 2

Some might be shocked that a $1,700 subwoofer comes with no wireless, auto-EQ, or app control features, but I wasn't. That's not what we're paying for here. What you're buying with the 13THX is what's seen in Monolith's astonishing specs and response curve (visible on the company's website): flat—and I do mean flat—response to below 18Hz, and a CEA output at 25Hz of 115 dB SPL at 10.6 percent THD. That sort of level at that frequency probably won't cause actual organ damage, but you will definitely feel it within.

Here's the short form: Unless you live in a decommissioned train station or are a convicted bass-felon with an ankle-monitor, Monolith's 13THX delivers more bass than you can use. Placed and balanced with care, you can be assured you are hearing whatever bass exists on a recording, at any level you desire. Period.

I balanced the Monolith sub from my listening position by both meter and ear for initial auditions in stereo with my sub-40Hz standmount monitors crossed over at 80Hz, and later at 60Hz. For all my subsequent music listening I used Roon, which implements two narrow filters that I tap to mitigate my room's two principal acoustical modes. Such filters are the principal virtue of room/speaker corrections system like Dirac or Audyssey: whether accomplished using software like Roon, or with hardware like an auto-EQ system, controlling the low-frequency resonances makes everything sound far, far better. Without it, you are in essence listening to the room, not the subwoofer.


Ordinarily, I spend most of any subwoofer review determining how loud/how low. But in this case, I already knew the answers up front: louder than you want, lower than you need. Beginning with my most familiar bass-ic tracks, such as Béla Fleck's "Flight of the Cosmic Hippo," which has a down-glissing bass ostinato reaching well below 30 Hz, I heard what I expected, which was powerful but timbrally intact rumblings, with pitches locked in perfect sync with the music and tightly controlled without overhang or "bloom."

So far so good: but this was audibly indistinguishable from my current sub, a sub-compact model that uses watts and equalization to cheat Sir Isaac, and which is precisely one eleventh the Monolith's size in cubic volume. So, what do you get from the 13THX for giving up a potentially sublet-able amount of floor space?

Volume, that's what. While my everyday provides all the bass I need at the levels I typically choose, it craps out at more extreme levels. Thanks to intelligent, well-implemented limiting and distortion monitoring, it does so gracefully by simply not getting louder, but crap out it does. The 13THX, in contrast, does not: the low end stayed in scale with the other seven octaves at any volume I could tolerate even briefly, awakening novel room-rattles including one in the floor that I could not get at from above or below. (Note to self: no room is ever completely de-rattled since somebody will always make a bigger subwoofer.)

I next cued up a fine Sony Classical recording of the famous Saint-Saëns "organ" symphony in C minor (24-bit/96kHz FLAC, Qobuz), which has a soft, sustained "pedal" A-flat in the first movement that plumbs below 26Hz. Though soft, this was palpably present, while the explosive organ, full orchestra, and symphonic bass-drum climaxes over the final minutes dealt literally room-shaking blows. The organ here scales down to a powerful 32Hz C, underpinned, depending on the organ and stops in use, by a 16Hz sub-C, and I felt like I was there in the same room with it.

But just how different were these relative to listening with my everyday sub? In the first instance, not at all at any volume I essayed. In the second, those huge, Wagnerian climaxes heard at my preferred volume, equivalent to a seat perhaps one-half to two-thirds back in "the house," was an almost even match. But when I turned the volume up perhaps 6dB, as if moving up to a Row 5 seat, the difference was clear: the Monolith retained the slam and physical sensation of a vibrating air mass (that 16 Hz?) in full scale, while my far smaller everyday woof, however valiant it tried, could not.


Of course, when somebody parks a '64 GTO in your driveway and tosses you the keys, you're not going to be content just driving it to the 7-11. So, I went looking for new bass worlds to conquer. After a couple of hours annoying my wife and the neighbors (the nearest is almost a quarter mile away), I ended up where I always do: "Bass I Love You," by electronica artist Bassotronics. This album has content—strong content—reaching well into the infrasonic region, so tread carefully. I'm a professional, so I didn't, but no worries: the 13THX did in fact produce sub-25Hz in-room levels well north of 100 dB SPL, with no audible distortion (at these frequencies distortion would have to be above about 30 percent to be evident), limiting, or rude noises. When reproduced loudly enough, this kind of bass-plus-infrasound can—and did—induce a sort of ear-sucking void between notes, like the effect you get at the beach when a sudden flaw in the wind seems momentarily to cancel all sound. Cool! But did the floor really ripple visibly?

The most difficult subwoofer characteristic to judge is smoothness through the crossover region. This depends so much on room effects, crossover and phase settings, and the response of the paired speakers, that any one evaluation is just about worthless. That said, I found the 13THX ridiculously easy to integrate. The two EQ curves, labeled "THX" and "Extended" and accessible via a back-panel toggle switch, give you one option; the former is a little flatter, the latter a little more extended. But the real influence over the bottom octaves comes from sealed vs. "bunged" operation. In my view, the 13THX is obviously designed to be run vented, either unbunged or with perhaps just one foam plug installed. It is flat from a bit over 100Hz down to about 40Hz according to Monolith's charts, which my experience gives me every reason to believe that there is little to be gained from sealed use. Below 40Hz, room-gain will typically bring the in-room level right back up, compensating the vented alignment's few-dB shelving action.

I wound up choosing single-bung option for most listening, as this delivers a nice little bump to the very lowest end by goosing infra-bass a dB or two at the limit of pitched audibility. If you want to impress your buddies by flapping their trouser legs with stuff like Bassotronics, this is the option you want.


Film sound, of course, is a big incentive in most purchases of subwoofers of this bulk, but I had little doubt of the 13THX's capabilities in that sphere. I streamed a variety of bass-active titles with great effect, including the more-than-usually ridiculous Amazon sci-fi-er The Tomorrow War. The first five minutes are a flat-out bass-fest, with every kind of movie soundtrack low-end effect on parade: explosive shockwaves, ominous rumbles, time-machine vibrations, and musical-score bottom-octaves. Unsurprisingly, the 13THX reeled all this off, at THX-ref levels, without breaking a sweat or emitting any uncouth boom, bloat, or burp.

I also spun through a handful of favorite bass demo scenes that hold up to the light of memory, including T-Rex footfalls from Jurassic Park and the train/bus crash from The Fugitive. One that I rarely omit is the cannon-practice scene from Master and Commander. With the Monolith on duty, the sharp, open-air crack of ignition was as startlingly crisp as I remembered, while the very low-frequency underpinnings were as prominent, and as deeply resonant, as I've ever experienced.

Okay, so the Monolith by Monoprice 13-inch THX Ultra Certified subwoofer is big, expensive, absurdly heavy, and visually about as elegant as a prizewinning pumpkin. It's also the most capable subwoofer I've ever enjoyed, and by a pretty wide margin. And it sacrifices nothing in blend-ability, or evenness and control through the crossover octaves. For those who have both the brass and the floorspace, Monolith's 13THX is unequivocally recommended.

Generally, I try to stay out of our readers' personal lives. But if you need more bass than this, there's something wrong with you. Seek professional help.


sirwilliamlee's picture

a rebranded SVS?