By aspect — in detail
Tonality
Contested · 10 srcSources split on what the MKIII actually is, not on whether it is good. One camp hears a balanced, versatile tuning that keeps the Monarch's monitor DNA and simply fills in the low end; another hears a deliberately coloured U- or V-shape — bassier, more energetic up top, and a clear step away from the MKII's neutrality. The same set gets described as studio-monitor, Harman-centric, U-shaped, V-shaped, warm and basshead by different reviewers, which is itself the useful finding: if you specifically want the MKII's leaner balance, the MKIII is not it.
Measured
TechPowerUp's IEC711 measurements show a bass shelf of roughly 9 dB gliding in from 250 Hz with extension below 20 Hz, an essentially flat response up to ~800 Hz, and a ~7 dB ear-gain rise from 1–3 kHz. RTINGS scores the bass "Emphasized (3 dB)", the treble "Balanced (-1 dB)" and the overall sound signature "Warm". THIEAUDIO markets the mids from 200 Hz to 800 Hz as "ruler-flat" — a claim the independent measurements broadly support.
Where it splits
A balanced, versatile all-rounder — the Monarch's monitor tuning with the missing low end finally filled in.42%
“Very little of the Monarch MKIII presentation is what I would consider ‘out of whack’.”
Marcus, Headfonics
A deliberately coloured, bassier U/V-shape — engaging and fun, but a real departure from the MKII's neutrality.58%
“There's of course the elevated bass but also the tonality is deliberately colored to work well with the likes of Asian pop and acoustic jazz.”
VSG, TechPowerUp
The generation's whole point, and mostly a success. Nearly everyone agrees the dual-DD isobaric module delivers deep, extended, textured low end with real physical weight — the fix for the complaint that dogged both earlier Monarchs. The dissent is about quantity and control rather than extension: a minority find the mid-bass dominant enough to sit on the mix on acoustic material, and a couple of reviewers think the outright texture and resolution fall short of the price.
“The newest Monarch MKIII has a gentle bass glide starting from 250 Hz itself which becomes a full-on bass shelf of ~9 dB with excellent extension all the way down to 20 Hz and below.”
VSG, TechPowerUp
“The MKIII has one of the most impressive bass presentations in the thousand-dollar arena.”
Yagiz, Headfonia
“The main thing that turned me off from the MkIII is its mid bass that does quite often tend to dominate the sound of whatever I'm listening to.”
Cockroach-Jones, r/iems (via RedditRecs)
Measured
The IMPACT² module puts two 10 mm composite-diaphragm dynamic drivers face-to-face in an isobaric chamber. TechPowerUp measures the result as a ~9 dB shelf with usable output below 20 Hz and, unlike the Harman in-ear target, no pronounced bass tuck — which is why it reads as having real mid-bass rather than sub-bass only.
⚠ vs. listeners — The absent bass tuck is exactly what one camp praises for body and the other blames for crowding acoustic mixes — the same measured choice, heard two ways.
Mids
Strong consensus · 9 srcThe clearest point of agreement and the line's inherited strength: flat and accurate through the lower midrange, natural in timbre, and highly resolving in busy passages. Several reviewers consider it the fix the Monarch needed — earlier generations were called thin or slightly recessed here. The one recurring caveat is the upper midrange, which is lifted enough that a couple of listeners find it a touch forward or hard on timbre.
“We get that same tuning philosophy here with an extremely flat response up to ~800 Hz allowing great instrument separation and accurate music reproduction even in extremely busy tracks.”
VSG, TechPowerUp
“I’m happy to announce that the midrange is fixed with the Monarch MKIII!”
Rudolfs Putnins, Headphonesty
“And speaking of instruments, the MkIII has great resolution in the midrange.”
Fc-Construct, Headphones.com
Measured
Measured flat to roughly 800 Hz, then a ~7 dB rise through the 1–3 kHz ear-gain region. TechPowerUp judged that rise slightly generous — "a bit too much upper mids energy for me" — which is the measured basis for the forwardness a few listeners report.
The set's most divisive property. THIEAUDIO deliberately raised the 15–20 kHz ultra-treble with newer Sonion electrostatic tweeters, and reviewers split hard on the result: one camp hears air, sparkle and extension with no fatigue, while another hears an exaggerated peak that manufactures detail and turns harsh — "fatiguing or harsh treble" is the single most-cited complaint in the community aggregate. Notably, the split does not track price or expertise; it tracks how sensitive the listener is to energy above the vocal range, and how loud they listen.
Measured
THIEAUDIO states it re-tuned the Sonion electrostatic drivers to raise output from about 15 kHz to 20 kHz. Headfonics measured only a very slight 7–8 kHz lift; Headphones.com's 711-clone graph shows an upper-treble peak but carries an explicit caption warning that a peak around 8–10 kHz may be a rig artefact and that measurements above 8 kHz are not accurate. RTINGS, on a different bench and target, scores treble amount at −1 dB.
⚠ vs. listeners — The lab and the listeners genuinely disagree here. RTINGS calls the treble balanced and the whole set warm, twice warning it may sound dull beside brighter rivals — while a majority of reviewers and owners complain it is too bright. The most likely reconciliation is that the disputed energy sits above the band a target-compliance score weights most: the deliberately lifted 15–20 kHz region, which different test rigs read very differently and which no target constrains well. Treat any single treble number here as rig-dependent, and trust the pattern of listener reports over any one graph.
Where it splits
Airy, extended and resolving without fatigue — the electrostatic top end doing what it should.43%
“I find the audible treble range to be very nicely balanced and aided by what seems to be a shift upwards in terms of upper-treble extension and headroom over the MKII.”
Marcus, Headfonics
Overcooked up top — an obvious ultra-treble peak that reads as manufactured detail and turns fatiguing or harsh.57%
“The treble response does feel weaker in execution compared to the rest though with ThieAudio still not having properly conquered the EST drivers for me.”
VSG, TechPowerUp
Soundstage
Moderate · 8 srcWidely reported as a highlight — wide, three-dimensional and unusually deep for an IEM, with several reviewers reaching for "holographic". The dissent is quiet but real: the most measurement-driven reviewer found the stage merely adequate and specifically noted the raised ultra-treble did not buy the extra space it was supposed to, and one owner heard width but not the depth others describe.
“Combine the additional space laterally and vertically with some impressive levels of micro-detail and you get a much deeper and more holographic-sounding presentation.”
Marcus, Headfonics
“The MkIII pushes the boundaries of the stage width even further. Peripheral instruments are extremely well defined at the very edges.”
Fc-Construct, Headphones.com
“soundstage feels correct enough even if personally I would have liked something wider and deeper”
VSG, TechPowerUp
Rated a strength alongside the stage: precise placement, clean separation and convincing layering in dense mixes. The one substantive objection comes from the most detailed comparative review, which found the image oddly shaped — an intimate centre and stretched edges with a thinner middle — and less natural than the MKII's more even spread.
“The imaging and the positioning feel accurate.”
Yagiz, Headfonia
“The image is presented with strong clarity in the positioning and separation between instruments, providing a holographic experience.”
Bloom Audio
“However, there’s a bit of a W-shaped imaging where there’s an intimate center image and stretched peripheries with less in between.”
Fc-Construct, Headphones.com
Detail
Strong consensus · 7 srcThe strongest consensus in the whole set after the midrange: resolution and detail retrieval rank with the best at the price, and even the reviewers most critical of the tuning concede it. The honest caveat, raised from two directions, is that some of the perceived detail rides on the lifted top end — and that the same revealing quality is unforgiving of poor masters.
“I’m tempted to call the MkIII one of the most resolving IEMs I’ve heard for complementary notes that play around the foreground.”
Fc-Construct, Headphones.com
“Both monitors excel in detail retrieval and resolution, with the MKIII accentuating low and high details more prominently.”
Yagiz, Headfonia
“Fairly resolving across the board”
VSG, TechPowerUp
Measured
RTINGS reports the MKIII reproduces audio without audible harmonic distortion even at louder listening levels, and TechPowerUp found no measurable change after 100 hours of playback — so there is no burn-in effect to wait for.
Dynamics
Contested · 6 srcSources split on slam. Most hear a fast, engaging presentation with a low end that hits hard and keeps pace on busy material — the dual dynamic drivers earning their keep. A smaller but well-argued camp says the fullness of the mid-bass rounds off transients: plenty of weight, but not the sharp, gripping punch rivals at the price manage.
Where it splits
Genuinely punchy and fast — the isobaric dual-DD delivers real impact and keeps up with dense material.67%
“the bass also hits quite hard while also being nicely textured and detailed”
VSG, TechPowerUp
Big but soft-edged — the mid-bass body rounds the transients, so it never quite grips the way rivals do.33%
“The one weakness in the bass is their dynamic impact. It doesn’t hit quite hard enough to make me sit up and take notice.”
Fc-Construct, Headphones.com
Comfort
Contested · 11 srcThe most common practical complaint and a genuine split. Everyone agrees the shell is flagship-sized — bigger than the MKII, with a nozzle over 6 mm — and that it protrudes. From there it divides by ear: reviewers with average or larger ears often find the contouring makes it more secure than the slimmer MKII, while a large share of owners report the nozzle pressing, ears going numb after an hour or two, or the shell simply not fitting. "Large and uncomfortable fit" is one of the two top cons in the community aggregate. Worth trying before buying if you possibly can.
Where it splits
Large but well-shaped — the aggressive contouring grips the concha, and many wear it for hours.56%
“Surprisingly, despite it being larger than the MKII, the Monarch MKIII felt more secure in my ear compared to the slimmer previous generation model.”
Marcus, Headfonics
Too big for a lot of ears — the shell and the thick nozzle press, numb or simply won't seal on smaller anatomy.44%
“As expected, the earshells are properly flagship-sized. Small ears will have trouble stuffing these dumplings in, so try before buying.”
Rudolfs Putnins, Headphonesty
A consistent strength. The hand-assembled medical-grade resin shells, the stainless nozzle and especially the upgraded 22AWG modular cable — with swappable 2.5 / 3.5 / 4.4 mm plugs — draw praise across the board, and the made-to-order faceplate and shell options are widely counted a genuine differentiator. Objections are minor and specific: the default faceplate is called a little plain, the stock tips restrictive, and one long-term owner reports the shell seam occasionally needing re-gluing.
“Consistent with nearly every ThieAudio IEM available, the Monarch MKIII exemplifies excellent build quality.”
Yagiz, Headfonia
“As crazy as it sounds, props to Thieaudio for including great stock cables in products that cost $1,000.”
Fc-Construct, Headphones.com
“My only complaint is that occasionally the glue will wear out and you will have to glue the seam back together”
Andrew Morgan (owner), THIEAUDIO
Measured
TechPowerUp measured each channel separately across three separate mounts and found the left and right drivers identical across the whole 20 Hz–20 kHz range — the kind of channel matching that warrants the flagship label, and reassuring for a made-to-order product.
Isolation
Moderate · 3 srcLightly covered but consistent: a vented hybrid, so isolation is a little above average for the type without approaching a sealed all-BA design, and roughly the same as the MKII. The included foam tips buy more isolation at the cost of extra canal pressure.
“The level of isolation is slightly above average for a hybrid but nothing to write home about and more or less the same level as the MKII.”
Marcus, Headfonics
“The MKIII is very comfortable, providing a good seal and isolation.”
Alex Schiffer, Major HiFi
Most reviewers call it a strong buy at $999 — several rank it with the best kilobuck IEMs outright, and one asks why you would spend more. A vocal minority disagrees, arguing that the technical margin over far cheaper sets no longer justifies the price, and the community aggregate is markedly cooler than the press: only about half of Reddit impressions are positive, which is low for a set this well-reviewed. Custom shells and faceplates add roughly $50–150.
Where it splits
A legitimate kilobuck standout — technically competitive with anything at the price and cheaper than several rivals it matches.72%
“I happily rank it among the Symphonium Helios and 64 Audio U4s as one of the best options for the $1,000 mark (and frankly, even beyond).”
Fc-Construct, Headphones.com
Hard to justify — diminishing returns are steep here, and much cheaper sets get most of the way.28%
“The simplest solution is 7HZ Zero 2. Then call it a day. Don't get scammed I am saying this from experience, I got up to monarch mk3”
33RhyvehR, r/iems (via RedditRecs)
