Seen above is one each of the size M silicone and foam ear tips that comes with the MOONDROP KATO, installed on the right ear bud and inserted into an artificial ear mold. I have averagely sized ears, and the ear mold seen above about perfectly represents my own experiences. Size M silicone tips are my go-to for testing since foam tips are not included by some. In this case, both had decent fit with my preference being the silicone tips. MOONDROP has something going on here with its new Spring silicone tips as they fit nicely and sound better to me, too. The size of the IEM shells is about average, and the design should be fairly comfortable for most people courtesy the soft curves gently caressing the concha and antitragus. I can't speak for the matte finish version, though, so keep that in mind. On the other hand, the colder polished steel version here can be less than ideal in the winter. These are heavier than the average IEMs at just under 9.5 g each. It's not enough to dictate comfort issues, but does make the need for a good fit all the more important. There isn't a lot of passive noise isolation, with the two vents addressing comfort in terms of pressure equalization more. Given these are still on the same inner surface, the need for a better fit once again comes up to ensure a good seal. Finally, the photos above also do a good job conveying why I don't like the stiff memory wire configuration on the stock cable that comes with the MOONDROP KATO. It is one of the hardest I have tried to date to re-shape, meaning I was fidgeting with the fit of the IEMs as the tension of the cable worked against the fit. That said, now a week or so into it, things have gotten much better to where it does seem to be an initial hurdle only.
The MOONDROP KATO uses a single dynamic driver per side, meaning the focus on a uniform driving force is key. There are several ways to get there, be it through the composition of the diaphragm and magnets or actual driving force, and of course any tuning done around it and the rest of the acoustic chamber. Even aspects such as the position and size of the voice coil relative to the diaphragm matter, and all this allows for marketing departments to go nuts when they try to make one product seem like the next big thing. MOONDROP is using a 10 mm ULT (ultra-linear-technology) driver that was developed for two years specifically to debut with the KATO. The company claims higher efficiency magnets—compared to what, I don't know—with a composite two-sided magnetic structure around the diaphragm itself to allow high magnetic flux to drive the third-generation diamond-like carbon diaphragm rapidly. DLC composite diaphragms are getting quite popular in this price range, and MOONDROP is pairing the diaphragm with an imported copper-clad aluminium voice coil. Everything in the acoustic chamber goes through finite element analysis for the design, including the airflow pathway and inner cavity design.
Driving the hardware takes no more than your average IEMs, with a rated impedance of 32 Ω and slightly higher than average sensitivity of 122 dB/Vrms, which in turn translates to 107 dB/mW. A standalone DAC/amp intended for high sensitivity earphones is not a bad idea thus, but harder to justify for the price tag of the MOONDROP KATO unless you already have one or plan to get these alongside other listening solutions. The lack of a 3.5 mm audio jack for most phones these days is another reason to consider a DAC/amp that takes digital input and provides a 3.5 mm jack since you will otherwise have to use an adapter or even a dedicated DAP. If not on the go, space is less of an issue, but the relatively short cable might be a potential handicap if connecting to a PC as the audio source. The rated 5–45,000 Hz range is also quite a stretch, but is based on the free-field potential—the company publishes the typical effective frequency range of 20 Hz to 20 kHz.
Frequency Measurement and Listening
I will mention that I have a general preference for a warm neutral signature emphasizing a slightly elevated bass and smooth treble range with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.
Our reproducible testing methodology begins with a calibrated IEC711 audio coupler/artificial ear that IEM buds can feed into enough for a more ideal isolation case. The audio coupler feeds into a USB sound card, which in turn goes to a laptop that has ARTA and REW running and the earphones connected to the laptop through the sound card. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/6th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average is taken of the three individual measurements for statistical accuracy. For IEMs, I am also using the ear mold that fits to the audio coupler for a separate test to compare how the IEMs fare when installed in a pinna geometry and not just the audio coupler by itself. The raw data is then exported from REW and plotted in OriginPro for easier comparison.
The IEC711 is such that you can't really compare these results with most other test setups, especially those using a head and torso simulator (HATS). The raw dB numbers are also quite contingent on the set volume, gain levels, and sensitivity of the system. What is more useful information is how the left and right channels work across the rated frequency response in the MOONDROP KATO, or at least the useful part of it. The left channel was separately tested from the right one and colored differently for contrast. I did my best to ensure an identical fit for both inside the IEC711 orifice, so note how the two channels are nearly identical through the bass and mids and within +/- 1 dB throughout the confidence region for the IEC711 coupler (until ~8–9 kHz), following which it is best to take things with a grain of salt. These are not top of the line (TOTL) IEMs, but there is channel matching, so it is good to see how close it gets. There was not any measurable burn-in effect, but keep in mind that MOONDROP tends to recommend a few hours of burn-in for all its dynamic driver IEMs, typically on the order of ~10–100 hours. I did let a mix of white/pink noise go through these for ~15 hours and checked again to be sure, but can't say I even perceived non-quantifiable changes to the output. Dynamics may have improved slightly, but good luck explaining that to a subjectivist. Take that for what you will, and also note that the response with the artificial pinna in place is quite impressive for how similar it is to the coupler itself, but that in itself does not mean it is better than others to actually listen to. The peak shift from 9 to 8 kHz does seem to be a measurement artifact; I've spotted it more often than not with other IEMs as well.
I re-wrote most of the rest of this page because things were originally quite confusing. You see, on the left above is MOONDROP's own factory measurement of the KATO relative to the company's VDSF target curve—a hybrid of the Harman (presumably 2017/8 in-ear) target and diffuse field neutral response. Those graphs are taken on a Brüel & Kjær TYPE 4128-C Head and Torso Simulator, meaning it can't directly be compared to my own results. But even so, the KATO appeared to have a more substantial bass response than my unit, especially compared to the MOONDROP Aria (2021) I have also compared to above. At this point, I also grew curious because my unit seemed to track the VDSF target quite well in terms of relative changes going from peak to valley to peak. Others with more experience reviewing and measuring IEMs also had the KATO come up with a bass response almost spot-on with the Aria (2021), although a few others popped up with the KATO showing a lower bass response, as with mine. Was this a one-off golden sample? Poor QC? Different measurement methodologies?
Noting that even the measurements without the artificial pinna showed this change, I waited to hear from MOONDROP rather than publish the review as soon as possible given this is a brand-new, highly anticipated release. This helped since MOONDROP confirmed the KATO is supposed to have a markedly lower bass response than the Aria (2021), and that was really all I needed. Insertion depths into the IEC711 coupler affect things higher up the frequency range too, but any degree of reproducibility is generally from a "perfect seal." The artificial pinna of course can change things, but not to where it explain this case, either. It's likely my sample is one of the better ones out there, and the other discrepancies may be a mix of sample variation and measurement methodologies. Regardless, knowing this unit is not a one-off as I previously thought, it means I proceed with the review.
It's a good thing too, since I personally really like the tuning here. I also agreed with MOONDROP that the bass response on the Aria (2021) was a touch too hot, although this is subjective, of course. Lovers of EDM and rock may appreciate the mid-bass energy there, although it can get somewhat bright later on, which accentuates this further. So I should state right away that if you are looking at the KATO as purely a better Aria (2021) in terms of better technical performance but similar tuning, look again. Tuning of the KATO is quite different, more in line with the more expensive Blessing 2, Variations, and Illumination MOONDROP offerings from what I can tell. If the KATO, which is the least expensive of that quartet, can be on comparison terms with those three, that's already praise so long as you appreciate the tuning. The breakthrough with the KATO was supposed to be ultra-low linear distortion in the 20 Hz to 10 kHz range, with THD under 0.05%. It seemingly goes up slightly when measured across the whole 20 Hz to 20 kHz range, and what that means to the end user is distortion on the level of full-sized electrostatic headphones. This is another way the company is marketing the KATO as a flagship, but it's with a big asterisk next to it in that it is the flagship for this driver tech and product family only.
To be more specific, this review unit of the MOONDROP KATO has a lightly elevated bass response, which is sustained from the lower mids to where there is warmth for rock and pop, but not enough energy for lovers of EDM and metal. There is enough impact behind the slam, however much that is, to keep macrodynamics in play, but without the punch of bass-heavy IEMs, such as the Campfiire Audio Honeydew. Then we get to a very smooth transition to the lower mids, which is probably my favorite segment here. Male vocals have enough energy to get me excited, and everything coming out is very smooth. There is good separation between mixed vocal tracks, as well as for distinguishing vocals and bass guitar resonances. Soundstage is alright, but coupled with the excellent imaging makes for an intimate listening experience that has its place.
The upper mids start to be more in line with expectations, and this is where my previous experiences with the MOONDROP Aria (2021) come in even though this review is likely going up earlier than that one. The two are tuned quite similarly in this region, just that the KATO has more detail and arguably more mature a response to the in-ear resonance compensation. MOONDROP's target here can still be somewhat shouty, but not as much as with the Aria (2021), and it does generally encompass in-ear resonances for most to where this tuning will feel more natural for more listeners than not—to some, it will sound too bright. This generally bodes well for pop, rock, and jazz music in my books before things start winding down in the highs. But minor sibilance with some tracks happened often enough to where I had to mention it. This did put a damper on what was otherwise a really good listening experience with enough room for string instruments when I listened to classical music. The commonly tuned region with the MOONDROP Aria (2021) is where the KATO really shines, with superior tuning and technical performance most of the way. The KATO does get dark earlier than I'd personally like, but I also recognize that this in itself won't affect many people. If anything, the dip at 12 kHz compared to the Aria (2021) is one I suspect people will like overall even if I personally don't. But that massive hike at 14 kHz with the Aria (2021) is one I also know will be universally deemed too harsh with instrument resonance ringing not being pleasant generally. This is where the KATO has a more sensible approach, which is why I appreciate it all the more over the Aria (2021). If the extremities at 7–8 kHz and the dip following it were not as high in amplitude both ways, I would have said my version of the KATO is my personal favorite; that is, until we get to the Campfire Audio Holocene or even ThieAudio Monarch.
This was my first time testing replacement nozzles that only differ in material, and I am merely whelmed by the effect. If I absolutely had to answer, I'd say I prefer the brass nozzle with some alleviation to the roll-off, and that I didn't notice any difference at frequencies past 10 kHz, as the graph above seemingly shows. It would be fair to say that there is really very little to distinguish the two nozzles, so you won't miss much if you stick with the default steel one. If you are sensitive to 8 kHz—think cymbals and string instruments—you perhaps may want to stick to the default stainless steel nozzles. This is even noting that the typical IEC711 coupler has a resonance peak at 8 kHz that can exaggerate things, so keep the comparison above to within itself as always.
Comparison to other IEMs
What we see above is a tuning comparison of the MOONDROP KATO to two other single dynamic driver IEMs in a similar price range I have tested to date, which are all recent releases and get compared to often. I do not have the Tanchjim Hana (2021) here unfortunately, which probably would have replaced the Campfire Audio Honeydew based on reader requests. For what it's worth, I would choose my MOONDROP KATO sample over the other two given it matches my listening preferences better. That said, the DUNU FALCON PRO is the better overall buy in my opinion because the included accessories are superior, especially the cable with the modular plugs. It also does the dynamic part of the dynamic driver IEM better, and so far does seem to be more consistent with lower sample variation. It does cost 15% more, so do keep that in mind. The Campfire Audio Honeydew is really not in consideration here unless you absolutely want deep bass and not much more. It also costs more than the other two, and over 30% more than the KATO at that!