Mon Acoustic SuperMon Mini Bookshelf Speaker Review

I knew very little about Mon Acoustic except that they were a high-end loudspeaker manufacturer based out of Korea, so I was a bit surprised when Audioholics editor-in-chief Gene DellaSala asked if I wanted to review a pair of their speakers. With enclosures made from aluminum, these are not your typical loudspeakers; to be honest, they are not quite like anything I have dealt with before. The metal cabinet is only one of the unusual design characteristics of their speakers, and there are a host of others that we will cover in this review of the SuperMon Mini. The Mini, as its name indicates, is a small loudspeaker designed for small rooms or desktop systems. At $2k per pair, they are geared toward those interested in luxury products and want to get the most out of a small space. They are manufactured and hand-assembled entirely in Korea. With an all-aluminum cabinet, the luxury aspect is certainly there, but what about the other elements that comprise a loudspeaker? That is what we will be examining in today’s review.

Packing and Appearance

The SuperMon Mini speakers arrived in a heavy-duty cardboard box. The speakers were fitted in some pockets of a soft polyurethane foam bedding. Most speakers ship in stiffer polyethylene foam packing, but that is to hold the speakers in place since normal hollow wood enclosures can not endure being thrown around as much as these metal cabinets. The goal of Mon Acoustic’s packing is more geared toward protecting the speakers from scuffs and scratches rather than protecting the cabinet from jolts and shock since these aluminum enclosures are far more solid than normal speakers and that isn’t as much of a concern.

Once unpacked, we are presented with some very upscale speakers that have a glistening aluminum body. The speakers that I was sent have a lilac-colored front baffle that gives them some flair, whereas an uncolored metal baffle might be a bit too business-like for some people’s tastes. Side panels have an undyed metallic luster, and there are some machined stripes on the sides. Custom colors can be ordered for an additional cost. There are many different colors available, and customers should get in contact with Mon Acoustics to order their desired color. These speakers have a stylized industrial look that would fit in nicely with modernist interior decor. They do not come with grilles, but there would be little point in buying a speaker with such a high-class metal exterior only to hide it behind some boring fabric. The front baffle has a shallow beveling at the top for a slightly sleeker look. I would imagine this shaping is aesthetically important since the wholly flat front baffle might be a bit blunt looking. Longitudinal edges have a rounding to help soften the appearance. An AMT tweeter is sunk into a deep waveguide that has a steep inward beveling, and the silvery woofer is sunk into the front baffle with a 90-degree beveling. The quality of the milling is excellent throughout. A Mon badge is printed in the lower part of the AMT plate. Screw heads are tastefully hidden by some magnets that make it look like the speaker was bolted together with flat head rivets that are flush with the front baffle. That is a beautiful attention to detail which is befitting the cost of these speakers. Model labeling and serial number are laser-etched on the rear. The SuperMon Minis look like they would serve well as a business executive’s desktop system. The aesthetics can not be faulted; these speakers look terrific.

Design Analysis

The SuperMon Mini is an unusual loudspeaker not just in enclosure composition but in the overall design. The base description is that it is a 2.5-way small bookshelf speaker with a number of unusual design choices. The obvious departure from the speaker design norm is the use of aluminum as cabinet construction material, so we will start our design analysis there before getting into the other unseen divergences from typical design practices. Aluminum is a great material to use as a loudspeaker enclosure when weight is not a consideration. It is very dense and so will make for an inert and resonance-free enclosure, and it is highly corrosion and heat resistant, especially the grade 6061 alloy used by Mon Acoustics. Furthermore, aluminum is also a great material for heat transfer, so the aluminum enclosure can also serve as a heatsink to disperse thermal buildup from the driver motors, and that should help dynamic range a bit by reducing thermal compression. The front baffle is 0.7” thick, the rear plate is 0.6” thick, and the side panels are 0.3” thick. There is also windowpane bracing around the midsection which is a part of the aluminum extruded main structure instead of being an additional welded piece. There is a spot-welded frame to hold the inner woofer which would add to the rigidity of the cabinet.

The internal construction wouldn’t be bad if these speakers of this size were made from some composite wood, but using aluminum with that thickness makes them positively boulder-like. On top of that, there is a fair amount of open-cell foam used as acoustic that lines the enclosure walls as well as the port. Anyone worried about panel resonances at all can breathe easily with the SuperMon Mini since this enclosure will be totally inert and vibration free. 

Some readers will see that 2.5-way design description and wonder where the other woofer is, since 2.5-way designs use multiple woofers, but only one woofer is visible on the Mini. This is where the term ‘isobaric’ comes in. Isobaric derives from Greek and means the quality of having equal pressure. For an isobaric loudspeaker design, the equal pressure refers to an air mass suspended in a chamber that is sandwiched by two active drivers which are moving in phase. So the Mini’s other driver is hidden and is mounted behind the exposed woofer at a halfway-deep point in the enclosure, and the two drivers enclose a sealed pocket of air between them. The reason to use this design is to get deeper bass from a small cabinet. The effect of having a pocket of air with unchanging pressure between two drivers is that the system retains a lower resonant frequency in a smaller cabinet by doubling the moving mass yet halving the compliance. It is like using one driver with a heavier moving assembly but a larger and softer suspension; it will have a low resonant frequency although at the cost of efficiency. The efficiency cost is minimized with an isobaric system since it halves the impedance and sensitivity.

Mon Acoustic’s take on an isobaric system is a bit different since the rear woofer has a low-pass filter and is only generating bass frequencies. That technically means that the air pocket between the woofers is not strictly static, because the excursion from the outer woofer is not matched by the inner woofer. But the volume of air needed to be moved to produce bass is much greater than higher frequencies, so the air pocket is largely being pushed around in a uniform manner due to the low frequencies for the most part, and the principle still holds. 

Using an isobaric system makes a lot of sense when metal is used as a cabinet material. Mass and weight add up very fast as the enclosure grows larger. Indeed, even though the Mini’s are quite small, they still weigh 11.5 lbs. each which is what I might expect of a well-built bookshelf speaker of twice their size. What is more, the outer woofer on the Mini is being tasked with playing up to treble frequencies, so a heavy driver wouldn’t have been an option since it could not serve as a wideband driver. The weight needed for a single driver to hit a lower resonant frequency in a small enclosure would have prohibited the ability to produce the midrange or treble frequencies that the engineer wanted.

The internal driver of the SuperMon Mini loads a port, and the port uses an elliptically shaped tube instead of a straight cylinder. Research by JBL and Bose has shown that similar-shaped ports will produce less turbulence than simple cylinders with some flaring on the ends. The port used by Mon Acoustics is a step up from the usual cylinder. The port is roughly 3” deep with a 1 ¾” diameter, and with dimensions like that, it is bound to have a somewhat high tuning frequency.

The crossover between the woofer and the tweeter is quite high at 6.8kHz. That means the tweeter is relegated to producing high treble only, and the vast majority of sound from the Mini will be coming from the woofer. With such a wide frequency band, a special wide-range driver is needed, because even though the woofer diameter is small at 4”, most 4” drivers would run into break-up modes by 6.8kHz. Break-up modes are the behavior that the cone starts to exhibit when it is moving so fast that it can no longer hold its shape. Larger cones will bend and flex at very high-frequency movement, and the frequency at which these break-up modes set in decreases as the size of the cone increases. The woofers used are 4” wide-range MarkAudio drivers. MarkAudio specializes in wide-range drivers that can maintain good performance out to high frequencies, so Mon Acoustics picked a good driver brand for this task.

One reason for giving the woofer such a wide-frequency range is that there will be no problems associated with a crossover circuit anywhere near the most important frequency bands. Most harmonic spectra from common musical instruments as well as human speech and singing are very low in amplitude by 7kHz. That means that the vast majority of the sound from these sources will be reproduced by the Mini’s woofer and not the tweeter. The advantage of this design decision is that there will be no phase rotation right in the middle of this important frequency range. Most 2-way or 2.5-way speakers have their crossover frequency somewhere between 2kHz to 3kHz, which is right in the middle of the spectrum of many human voices as well as acoustic instruments. The problem with that is, even if the crossover circuit is perfectly executed so that the frequency response exhibits no sign of the crossover point, there will still be phase rotation around the high and low pass filters used to create the crossover. While it was previously thought that phase distortion was not a major audible problem unless it was extreme, there has been some research in the last few years that suggests these types of phase artifacts can degrade speech intelligibility. In other words, the SuperMon Mini should have excellent speech intelligibility due to the absence of a crossover circuit in a common speech frequency spectrum.

The crossover itself uses some very heavy-duty components such as Mundorf large film capacitors, air-core inductors, and massive resistors. The robustness of these components is very likely overkill, but it’s better to have it and not need it than to need it and not have it. These are all very low-tolerance components, and given their size and build, the capacitors should hold a stable capacitance value for a very long time to come instead of drifting in value like a ceramic capacitor. These large film capacitors are much less affected by heavy use, so they won’t get hot and change their value from thermal effects.  

While the Mini is a small speaker, it is using some pretty beefy five-way binding posts. When I asked Mon Acoustics how much power the Mini’s could handle, they advised 30 watts from tube amps, 100-200 watts from class AB, and 150+ watts from class D. Over 100 watts seems like a lot for such a small speaker, but the isobaric woofer system plus an AMT tweeter should be able to take a lot more power than a typical small speaker.

The Mini’s tweeter is a small AMT tweeter. It is crossed over at such a high frequency that it almost functions more as a supertweeter than a normal tweeter. The tweeter is sunk into a steep waveguide that has been milled into the front baffle. This waveguide looks like it is serving a contrary function to the 4” woofer. The woofer is bound to have wide dispersion out to a high frequency, whereas the waveguide on the tweeter looks like it would significantly restrict dispersion. That could set the drivers up for a directivity mismatch, but we will get a look at its nature in the measurements section of this review. Another potential problem with the waveguide is it could create a hefty amount of diffraction. In narrow waveguides like this, diffraction is caused when sound from the transducer diaphragm experiences a lot of reflection off the inner sides of the waveguide. These reflections can interfere with the direct sound of the tweeter diaphragm and cause comb-filtering patterns in the response or other types of phase distortions. This could be exacerbated by the use of a small AMT tweeter that would naturally have a very wide dispersion, so it is throwing a lot of acoustic energy off to the sides. On the surface, a waveguide of this shape would seem to be suboptimal for this loudspeaker design, but it’s possible that it was necessitated by manufacturing practices where a wide, shallow waveguide would have been much more difficult to execute in milling aluminum. And with such a high crossover frequency to the tweeter, I wouldn’t expect the suboptimal waveguide shape to turn into a major audible problem since it isn’t touching midrange frequencies at all. 

Zooming out, we have a small speaker with an excessive build quality that is trying to get some bass out of a small enclosure through an isobaric driver arrangement while relying on a wide-band driver to carry most of the sound to avoid any crossover circuit issues. Mon Acoustics have pulled some clever engineering moves to pull this all together, but let’s see what it all sounds like in practice…

Listening Sessions

Most of my listening with the SuperMon Minis was done in an office room with the speakers placed about three feet in front of me on an office desktop with some desktop speaker stands to angle them at my listening position. It is not the ideal space for speakers, but it is an intended environment for the Minis that many users will use. This being the case, I decided to evaluate them in the conditions that they will probably be used in by most owners. The Minis are intended to be placed near a back wall (Mon Acoustics recommend 6-7 inches of distance from the back wall) to properly load port output. The receiver used was a Denon 4311CI AVR with a PC as the source. No equalization was used, and no subwoofers were used unless stated otherwise.

Music Listening

A very nicely performed and recorded album that I recently discovered is Christina Vane’s “Make Myself Me Again.” This is a bluesy country album that was released in early 2022 that has a personal sound unlike so much other country music that is mixed to sound like arena rock music. Vane’s vocals are the star of this show, but she is a skilled slide guitar player as well, and this album is a great showcase for her guitar chops. She is backed by a bevy of other talented instrumentalists in the country and bluegrass scene, and we hear accompaniment by fiddles, harmonicas, banjos, bass guitar, acoustic guitar, and percussion. The album as a whole is an intelligent and engaging listen, and it deserves attention from more than just country music fans. I streamed this album in Qobuz at a 24-bit/96kHz resolution.

From the start of the album, it was apparent that the Minis imaged superbly. Vane’s voice as well as her slide guitar took dead center stage between these speakers, even placed back on a desktop. Instruments had their positions nicely defined as well. As an example, on track 3, “River Roll,” it was easy to hear the banjo’s placement on Vane’s far left and a fiddle just to her right. Lazy mixing would just place everything in the center, but the sound engineer for “Make Myself Me Again” decided to spread the performers across the soundstage more, and the Mini’s reflected that quite nicely. Since the speakers were positioned at a somewhat lower height, the performance did sound slightly lower in altitude than my ears, but I don’t think any speaker could image differently when the speaker is lower than the listener. This is easily solvable by getting desktop speaker stands to elevate the speakers to my ear height, but the slightly lowered soundstage didn’t bother me enough to go out and get new desktop speaker stands. The Minis articulated Vane’s voice with precision, and the instruments were rendered with detail as well. The crunchiness of the distorted guitar on “Little Black Cloud” was vividly reproduced, and the Minis gave it a thick, crisp sound. 

The Mini’s had bass, and the bass guitar properly underpinned the music here. A nice demonstration of that occurs in the track “Old Enough.” To be sure, we are talking about mid-bass. Most of what a bass guitar produces lies in the mid-bass region. There is no consensus on what frequency range exactly constitutes mid-bass, but I am just going to offer an off-the-cuff definition of 70Hz to 160Hz, with maybe 160Hz to 380Hz being upper-bass. I would say that bass in general is sound that covers the fundamental frequencies of music and speech and also has a physical dimension to it that just isn’t there at higher frequencies. That tactile quality seems to be gone by 400Hz, at least for me. But however you want to subdivide bass ranges, I doubt anyone would argue that the Minis weren’t able to bring enough bass to make these tunes enjoyable. Larger speakers would certainly have given more muscle to the lower bass guitar notes and bass drums, but those sounds were present enough from the Mini’s that the music didn’t sound thin.

I was deeply impressed with the early music vocal ensemble Graindelavoix’s rendition of Josquin Desprez’s works, so I looked through their back releases to hear their other performances. One that caught my attention was “Messe de Nostre Dame” by Guillaume de Machaut. Machaut is one of the leading European composers and poets of the 14th century, and “Messe de Nostre Dame” (“Mass of Our Lady”) holds a place as one of the towering achievements of medieval music. The influence that this mass has had on subsequent sacred music cannot be overstated. Graindelavoix gives it an extravagant treatment, and the celebrated early music record label Glossa provides an exquisite production that makes this album a major event for fans of medieval music.   

Again, the first aspect of the sound from the Minis was how well they could image in a desktop environment. While the harmony of the singers was excellent, they weren’t mixed to blend in together as an indistinguishable choral mass but rather as an assembly of individual voices. The positions of the individual singers were readily apparent in the soundstage projected by the Minis. The timbral character of each of the singers came through as well thanks to the elocution of the Minis. This helped me differentiate each of the tenors and baritones as well as hear that there was one bass whose voice was so deep he might well have been a basso profundo. Graindelavoix’s voices were beautifully presented by the Minis. They sounded natural and full. The acoustic environment of the recording was also translated well, and even though I was listening in a near-field setting, I could still hear what it was like to have a front-row seat at St. Augustine’s Church in Antwerp where this album was recorded. I am not sure how similar this performance is to the originals done in Guillaume de Machaut’s time, but I found this music to be surprisingly complex and emotionally vibrant, especially for a 14th-century mass. It’s a long way from gothic chants of earlier sacred music, and I found myself captivated for the entire 72-minute running time. The SuperMon Mini’s proved to be a terrific tool to facilitate this experience.

It is not surprising that the avant-garde American composer Michael Gordon and famed San Franciscan string quartet Kronos Quartet had been friends for many years since each of these eclectic artists has been pushing the boundaries of instrumental music for decades. I was therefore not at all surprised to find an album of the Kronos Quartet’s performances of Gordon’s compositions, but even so, I was intrigued, because there was no way this music could be boring. “Michael Gordon: Clouded Yellow” features three pieces of music commissioned over the years as collaborations between Gordon and the Kronos Quartet. Obviously, this music is going to be a long way from the sedate Baroque classical music that comprises so many chamber music releases, but I wondered how far out in the left field would it go? This is something that speakers like the SuperMon Minis should excel at, so I queued up the album on Qobuz to give it a spin. 

Again, the soundstage projected by the Minis was striking considering that I was using them as desktop speakers. However, while the violins didn’t sound bad, there was a nasal quality to them that I attributed to acoustic reflections off the desktop. I moved them from some desktop speaker stands that merely angled the speakers upward without raising them very much to the top of some tower speakers that were flanking the desk. In this placement, they were much more out in the open, and so that nasal quality was gone. There was still some slight heaviness in the sound that I blamed on the acoustics, but later, after having measured the speaker, I saw in the measurements that there was a mid-bass bump that did give the lower notes a bit more thickness. It wasn’t severe, but it did add some coloration to the sound of this particular album. The Mini’s lent the violins and viola a vibrance and dynamism that belied the small speaker size; on the latter half of the second track, “Potassium,” the repetitive sharp bowing created a tremolo effect that sounded like the instruments were going to leap out of the speakers. The Minis also managed to effect some very otherworldly imaging on some sampled children’s voices in “The Sad Park, Part 1,” where a reverberant child’s voice was stretched over time and wandered back and forth in the soundstage. Much of the music played by the Kronos Quartets was dissonant, and, layered on top of the twisted sampling, summed up to an uncanny and surreal effect. This was challenging music for sure, and the Minis gave it all the queasy energy that was no doubt intended by the artists involved.

Moving on to a non-acoustic recording, I listened to an electronic music album titled “Don’t Forget Me” by w o s u 命 from the subgenre of Dreampunk. Dreampunk is heavily influenced by Blade Runner and future-set anime, but it isn’t merely a generic cyberpunk soundtrack. Rather, it is emotionally charged and evokes a sense of melancholy and anxiety about the social isolation of urban life. It is largely produced by synthesizers, samplers, and drum machines, and I wanted to hear what the Minis could do with a wholly artificial sound rather than a sound that is engineered to seem natural.

For this album, I brought the speakers into my home theater room as an experiment to see how they would handle use as a typical hi-fi loudspeaker. I also gave them a subwoofer with a 110Hz crossover frequency to give those 4” woofers a break since there was some significant bass in this music, and they didn’t have as much of an advantage in boundary reinforcement or near-field listening to shore up the low end. Needless to say, they sounded much more open and had a greater sense of space. The extra bass provided by the subwoofer was also a marked improvement and lent them an authority that they didn’t possess on their own (not that anyone should expect a loudspeaker with a 4” woofer to have subwoofer level bass). The Minis offered a wide and enveloping sound that is very much a goal of this music. The soundstage seemed to extend well beyond the width of the speaker positions. The sweeping synths and reverb-drenched percussion washed over the breadth of the soundstage and created a soundscape that I could get lost in. The transition from a three-foot listening distance to an eight-foot distance did not perturb the Minis, and they still had enough dynamic range to deliver enough loudness to give “Don’t Forget Me” some verve, although the inclusion of the sub really assisted in that respect. There is no doubt that these speakers had their dynamic limits, but I listened to this album at the same level as I would any other speaker, and I was happy with how loud they could get. In retrospect, perhaps I shouldn’t have been surprised at how good the Minis sounded in my home theater given that they managed to pull off a decent sound in a very compromised desktop setting, but they did, and I quite enjoyed listening to this atmospheric electronic music with these speakers. 

Movie Watching

One movie that had been lingering on my watch list for a while was “State of Play,” a 2008 political thriller starring Russel Crowe and Ben Affleck. This movie is about a rising-star congressman whose research assistant is found murdered. A journalist that is an old friend of the congressman runs into a web of conspiracy when he proceeds to investigate the murder. This movie looked like a typical big-budget thriller with much of the plot being dialogue-driven rather than action-scene-driven, and I thought that would be a good test of the Mini’s ability to reproduce standard-issue Hollywood fare. I decided to avoid something with an extremely wide dynamic range with lots of deep bass since there is no point in throwing a lot of deep bass at a speaker that is not geared to handle that, but it should be capable of catching most of the sound mix in a talky thriller such as “State of Play.”

“State of Play” turned out to be a perfectly serviceable political thriller, if not a particularly memorable one, but it was engaging while it lasted, and the SuperMon Minis helped to make it an enjoyable experience. Dialogue was always crystal clear and intelligible, and the snappy patter and shorthand of the veteran newsroom crew were never difficult to follow. Alex Heffe’s orchestral score was given a detailed and vibrant accounting. The orchestral strings that coincided with shocking plot revelations had an unexpected amount of punch considering the size of the speakers. Once again, imaging was stellar, and speakers adroitly tracked the voices to the actors’ on-screen positions. The Minis can’t duplicate the larger-than-life sound of an Imax theater, and no speaker of its size ever could, but it can deliver a satisfying sound for something that doesn’t depend on epic action scenes to be watchable. It exceeded what I would have expected from a pair of small desktop speakers. 

For something that puts a bit more emphasis on sound effects and especially spatial effects, I watched “Malevolent,” a 2018 supernatural thriller that I hadn’t seen before. “Malevolent” is about a team of con artists that pretend to be exorcists and are hired to go into ostensibly haunted houses and rid them of their ghostly presence. They stage ghost cleansing rituals with hidden trickery to bilk homeowners, and since the homes are never actually haunted, it is a scam with little blowback. Everything goes well until they are hired to cleanse a home that is actually haunted. The plot of cynical, non-believing ghost hunters who unwittingly encounter a real haunting with dire consequences has been done a lot over the past decade (thanks to the success of the film “Grave Encounters”), but I still watch these movies because I love that “Oh s**t” moment when the fraudsters realize they have run into the real thing. Since so much of the action in these types of movies is relayed off-screen as sound, I do think they make a good test of how well a two-channel system can reproduce a movie soundstage that puts heavy emphasis on sound effects imaging. 

For this film, I had set the speakers up in my home theater and used a subwoofer, so the Minis were alleviated of a congested desktop setting but now had to power a home theater room, albeit with the help of a subwoofer. “Malevolent” was not filled to the brim with jumpscare ‘boo’ moments, but it did have its share of creepiness, and a lively sound mix was instrumental to its success. The location of the haunting turned out to be a mansion that served as a foster home where a dozen orphans were murdered 15 years before, so the sound mix featured lots of disembodied giggling and whispers as they taunt our team of fraudulent spiritualists. The Minis reproduced these off-screen sound effects with eerie realism. The score by Al Hardiman abetted the tense atmosphere, and it was intensely expressed by the Minis. As with “State of Play,” character dialogue was always totally intelligible. Even though the movie took place in a murky old mansion, the sound mix as reproduced by the Minis gave clarity to the events, so I was never left unsure of what was occurring. Another factor that might have contributed to that is that I realized about an hour into the movie’s running time that I had seen it before when it was first released. It wasn’t a bad movie, but I suppose it didn’t leave much of an impression upon my first viewing, especially when it took me so long to recognize it. Nonetheless, I enjoyed my unintentional second viewing of “Malevolent.” With reasonable expectations of what small speakers can do, my viewing experience proved that the Minis can be used as speakers for movie content very nicely.