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Mon Acoustic SuperMon Isobaric Measurements and Conclusion


The SuperMon Isobaric was measured at a height of 4 feet at a 1-meter distance from the microphone, and the measurements were gated at a 5-millisecond delay. In this time window, some resolution is lost below 600 Hz and accuracy is completely lost below 300 Hz. Measurements have been smoothed at a 1/12 octave resolution.

SuperMon Iso 3D waterfall response

SuperMon Iso 2D waterfall response

The above graphs depict the speaker’s lateral responses out to 90 degrees in five-degree increments. More information about how to interpret these graphs can be read in this article: Understanding Loudspeaker Review Measurements Part II. The overall response shown here is not bad but there are some oddities. Firstly, the treble at and around the on-axis angle seems to be a bit hot above 5kHz. By the 20-degree off-axis angle, it is level-matched with the lower frequency range, but as we move inward toward the on-axis angle it does become a bit elevated, perhaps 3dB hotter than the average below that range. I didn’t notice an especially hot treble in my listening, but I didn’t listen to the speakers at an on-axis angle. The mid-range from 500Hz to 3kHz is generally well-controlled, and that is where the heart of most music is, so it was important that the SuperMon Isobaric got that right. There seems to be a slight lowering of amplitude below 500Hz that may have contributed to the weakness in bass that I heard, at least before I equalized them, but the main explanation for that will follow when we examine the groundplane measurement of the low frequencies.

SuperMon Iso Polar map 

The above polar map graphs show the same information that the preceding graphs do but depict it in a way that can offer new insight regarding these speakers’ behavior. Instead of using individual raised lines to illustrate amplitude, these polar maps use color to portray amplitude, and this allows the use of a purely angle/frequency axis perspective. The advantage of these graphs is they can let us see broader trends of the speaker’s behavior more easily. For more information about the meaning of these graphs, we again refer the reader to Understanding Loudspeaker Review Measurements Part II.

The SuperMon Isobaric’s front radiation pattern is a bit ragged but generally is fine with no major bursts of energy or nulls at off-axis angles. One unusual feature is that we can see a small dip on and around the on-axis response just above the crossover frequency. This suggests that there is not perfect phase alignment between the tweeter and woofer, at least on-axis with the tweeter. In that same region, there is also some extra off-axis energy. This is occurring at the tweeter level, and this attribute would certainly change with height, so a higher or lower angle might correct this minor error. Something else interesting to note is that the tweeter manages to keep a somewhat wide dispersion out to a relatively high frequency. At 1.5”, the SEAS Exotic is a large dome tweeter. Typically these kinds of tweeters will begin to constrict dispersion at relatively low frequencies. This tweeter does constrict its dispersion somewhat above 5kHz, but it doesn’t get really narrow until above 10kHz. The listener could be listening at a 30-degree angle and still be met with high treble. It’s would be an unusually broad angle of high-frequency energy for a large dome, except that it seems as if the tweeter had been voiced a bit hot to achieve this effect. 

SM iso response per angle graph 

The above measurements compare the on-axis response of the SuperMon Isobaric to a couple of off-axis measurements. We are doing this to illustrate the optimum toe-in angles for those users who are looking for the most neutral sound. As we saw in the polar map, the on-axis angle has a null around the crossover frequency indicating a phase conflict, at least for the point in space where we measured. Moving off-axis smoothes out the irregularities from the on-axis angle and can yield a fairly neutral response. From 20 to 30 degrees, the response becomes relatively flat, which can be seen on the 25-degree curve. Moving even further off-axis, we can see the tweeter’s dispersion narrow, and the higher frequencies become rolled off. Listeners are likely to end up in a neutral response angle if they position the speakers to straight face forward in a parallel aim with no-toe-in angling. I would recommend users start with this type of placement in setting these speakers up.

SuperMon Iso low-frequency response 

The above graphs show the SuperMon Isobaric’s low-frequency responses that I captured using groundplane measurements (where the speaker and microphone are on the ground in a wide-open area). There are two curves here: the purple curve is the speaker measured with the microphone 2 meters in front of it, and the brown curve is measured with the microphone 2 meters behind the speaker. One feature of the front-measured response that leaps out is a high-Q dip just above 100Hz. While that may have contributed to the lessened bass response that I heard, what I heard was not quite a null, but rather an overall attenuation of low bass. This null occurs in front of and on the sides of the speaker, and I would guess that the isobaric loading design of the speakers creates some kind of sharp cardioid null. Rear-generated output by the port would help to fill it in somewhat in-room. The cause of the reduced bass is better explained by the overall lowered output below that null. Everything below 100Hz looks to be at least 3dB softer than the range above the null. Something else to note is that this speaker is tuned quite deeply for a stand-mount speaker. The response extends well below 40Hz before it even begins to roll off. That is more like the bass extension that we typically see from floor-standing speakers, not stand-mount speakers.

SM Impedance 

The above graph shows the electrical behavior of the SuperMon Isobaric. These are unusual impedance curves, to say the least, but they aren’t bad or especially problematic. The only spot of concern is 100Hz, which dips down to 4 ohms along with a very steep phase angle. That is going to be rough for a cheap amp, but no one who buys these $25k speakers is going to pair them up with a cheap amp, so there isn’t anything to be concerned about here. One unusual feature we see is evidence of two resonances in the low frequencies; one for the port tuning at 35 Hz, and another at 100Hz, which is presumably related to the isobaric design. The tweeter’s impedance seems relatively high for a dome tweeter, and I think that is due to some resistor padding in the crossover circuit on the SEAS Exotic. I measured the sensitivity to be 88.5dB for 2.83v at 1 meter, and that is pretty close to the manufacturer’s spec of 89db. This is about the sensitivity I would have expected of a large stand-mount speaker, so no surprises there. Any decent amp should be able to make these speakers get loud. However, I would recommend a somewhat beefy amp for those who want to give the bass more muscle via equalization, which I think will be a lot of owners.


We will wrap this review up by briefly going over the strengths and weaknesses of the product under review. As always, we will start with the weaknesses, since I am the kind of person who likes to get the bad news out of the way first. The SuperMon Isobarics do have their flaws. The most prominent flaw, one I have already discussed at length, is that the entire lower bass frequencies have been significantly attenuated. This can be remedied by a simple equalization curve, but I would have hoped that loudspeakers as expensive as these wouldn’t need equalization to make sub-100Hz bass levels match up with the higher frequencies. I think that using an isobaric design has likely caused more problems than it has solved in this instance.

 SM pair11

SM Mon badgeOn top of the missing bass, the frequency response at and around the on-axis angle is a bit rough in treble frequencies. Listening to the speaker head-on can be piercing with certain content at times due to the prominent treble. This is easily solvable by listening with only a mild to no toe-in angle where the response becomes fairly neutral at the listening position. Nonetheless, I have had plenty of less expensive speakers that didn’t have this problem. I believe the root cause is that if the tweeter were level-matched with the woofer at an on-axis angle, its off-axis energy would be fairly low, and it would end up with a mismatched dispersion with respect to the woofer. So Mon Acoustic chose to have better off-axis behavior at the cost of a smooth on-axis response. While this issue is solvable for a single listening position by merely repositioning the speaker to an angle of response that suits the listener’s ears better, it is not easily addressed with equalization for a broader listening area.

With my complaints out of the way, let’s now get into compliments. With EQ’d bass and correct placement, the SuperMon Isobarics can sound terrific. They do take some work to get there, but they can certainly get there. The effort involved in attaining a great sound from these speakers will inevitably be a turn-off for some people, but there are those audiophiles for whom that would actually be a draw. The soundstage and imaging are excellent. The speakers can have a good dynamic range if given enough power to compensate for bass equalization. The midrange performance is generally good out of the box on and off-axis, and, as we noted before, that is where most audio content lie. I enjoyed listening to them once I had them set up optimally for my tastes.

Outside of their sound, the build quality of the SuperMon Isobarics is nearly as good as can be had. It would be difficult to make a more inert, dense enclosure. Perhaps a thick marbled stone would be even more enduring and massive? Or maybe a denser metal like titanium? But to have a large stand-mount loudspeaker built out of aluminum is pretty over-the-top. The Isobarics feel like they look too. Picking one up is akin to lifting a boulder. At 80 lbs. each, users will need to be careful when handling these speakers. As we said about the SuperMon Minis, if taken care of, these speakers could potentially last a very long time. The soft components are going to be the limiting factor in the lifetime of these speakers, but if they are kept in a climate-controlled environment without experiencing too many temperature extremes or humidity cycles, then these speakers could last many decades.

Their appearance is pretty stunning- as any fully metal loudspeaker would be. Owners looking for a speaker that looks high-end without being over-stylized have a great choice in the SuperMon Isobarics. These are not speakers that will meekly blend in with the decor; these are speakers for audio lovers to proudly display. Visitors will notice them, and they will likely be the subject of conversation.

SM pair

SM labelWhile getting to know the SuperMon Isobarics proved to be a bit frustrating at first, once I did get a grip on them, I could elicit a great sound and had a very enjoyable experience overall. But to focus on the sound alone is to partly miss the point of loudspeakers like these. These are not just about the end result but how that result is arrived at. Rolex watches are not desired for how well they track time, but for the mechanical engineering used to accomplish that objective without resorting to quartz crystals or other digital means. Similarly, the use of aluminum as an enclosure material and isobaric loading of the woofer plays a role in the desirability of these speakers, even if those design aspects don’t necessarily make them more accurate for audio reproduction (although I have no doubt that Mon Acoustic does believe that those aspects assist in superior sound quality).

Some audio enthusiasts just view audio equipment as a means to an end, but others celebrate the method by which that end is achieved. Most readers knew which side of that line they stood on before they started to read this review, so my guess is that reading this review won’t do a lot to change the minds of those who already knew about these speakers. As for myself, I can appreciate both perspectives, but I do lean more toward the function-over-form, so I can’t say that the SuperMon Isobarics would be my first choice if I had $25k to spend on a speaker pair. For my own tastes, too much of its design budget was allocated to aspects that don’t contribute to sound reproduction (again, I am sure that Mon Acoustic would disagree on this point). I can say that I could easily live with a pair if someone just gave some to me and that the past few months living with them have been a delight.  

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
Build QualityStarStarStarStarStar
Treble ExtensionStarStarStarStar
Treble SmoothnessStarStarStar
Midrange AccuracyStarStarStarStar
Bass ExtensionStarStarStarStar
Bass AccuracyStarStarStar
Dynamic RangeStarStarStarStar
Fit and FinishStarStarStarStarStar
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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