By aspect — in detail
Tonality
Contested · 11 srcThe most contested question about the set: warm all-rounder or bright, revealing one? In STANDARD mode most hear a studio-neutral, mildly V-shaped balance with sub-bass lift and upper-treble air; the RUMBLE switch adds warmth and slam on demand. Fans call it balanced and versatile; a sizeable camp (including listeners who expected the older Monarchs' warmth) hears it as leaner, brighter and more energetic than they wanted.
Measured
ThieAudio voices STANDARD to a studio-neutral target with a ~10 dB sub-bass shelf cut sharply at 150 Hz and an airy upper treble; the RUMBLE switch adds ~3 dB across the sub-bass shelf (to ~13 dB) plus ~2 dB at 200–500 Hz, making the profile thicker and warmer. On the B&K 5128 (Hawaii Bad Boy's database) it reads as an upward-tilted, sub-bass-boosted set, not a warm/dark one.
Where it splits
A balanced, versatile all-rounder — studio-neutral in STANDARD mode, with the switch adding warmth and slam on demand.55%
“Despite its V-shape, it is both very balanced and very natural.”
Hifitopia, HiFiTopia
Leaner, brighter and more revealing than a 'warm all-rounder' — neutral-bright and energetic in standard mode, not the laid-back set some expect.45%
“flips it from a neutral-bright sounding IEM into one that presents bass first, midrange second.”
Fc-Construct, Headphones.com
Quality is rarely questioned; quantity and character split by taste and by switch. Most hear the IMPACT² low end as deep, fast and textured, with the mid-bass deliberately pulled back for a clean midrange — and praise the RUMBLE switch for adding real slam without bloat. A critical camp finds standard mode lean and unremarkable for a kilobuck, and rumble mode a touch overbearing or loose.
Measured
The IMPACT² system (dual 8 mm composite-diaphragm DDs in an isobaric chamber) puts a ~10 dB sub-bass shelf with a sharp 150 Hz low-mid cutoff in STANDARD; RUMBLE lifts the whole shelf ~3 dB (to ~13 dB) and adds ~2 dB at 200–500 Hz.
⚠ vs. listeners — The sharp 150 Hz cutoff keeps mid-bass low, so the same tuning reads as 'clean and fast' to most and 'lean, limited slam' to others — how much physical weight you feel depends on the track, the tips and which switch position you use.
Where it splits
Deep, fast and textured, with a genuinely useful switch — clean and controlled in STANDARD, real slam on tap in RUMBLE.57%
“The MK4 is quite rich, punchy, and fast at low frequencies.”
Hifitopia, HiFiTopia
Underwhelming for the price — lean and unremarkable in STANDARD, or a touch overbearing and loose in RUMBLE.43%
“It’s better on the Monarch MKIV, but there’s nothing special about the presentation.”
Fc-Construct, Headphones.com
Mostly a highlight, with one loud dissent. The majority hear natural, rich, lifelike vocals and instrumental timbre — often the favorite aspect of the set. A prominent critical outlet hears the midrange as technically clear but dry and 'sterile,' short on musicality, and a couple of listeners find vocals pushed too forward.
Where it splits
Natural, rich and lifelike — one of the set's highlights, especially vocals.67%
“Balance and naturalness dominate the midrange.”
Hifitopia, HiFiTopia
Clear but clinical — 'dry and sterile,' short on musicality, or pushed too forward.33%
“But it sounds somewhat dry and sterile to me.”
Fc-Construct, Headphones.com
The set's signature strength and its most common complaint at once. Nearly everyone agrees the top end is extended and airy — the source of its space and detail — thanks to a treble lift and an EST-fed peak up top. The split is whether that energy is a strength or too much: treble-sensitive listeners find it hot or fatiguing, especially at volume, and a couple of reviewers flag its control as merely 'borderline' for the price.
Measured
The MKIV retunes its EST tweeters to the 10–40 kHz region and adds a treble lift plus a peak up top (owners point to a rise around 10 kHz and a spike near 15 kHz) — which is why air and detail read as elevated, and why bright or loud listening surfaces the fatigue complaints.
Where it splits
Extended, airy and resolving — the source of the set's air and space, and non-fatiguing to many.46%
“the MkIV sounds open, airy, and gives you a better sense of space.”
Cockroach-Jones, r/iems
Energetic to a fault — control is only 'borderline,' and it turns hot or fatiguing for treble-sensitive listeners, especially loud.54%
“control is borderline. It’s good in the control department but not the best, which reminds us why this headphone isn’t $3000.”
Hifitopia, HiFiTopia
Soundstage
Moderate · 7 srcA near-universal highlight. For an IEM the stage is repeatedly called wide, deep and holographic, extending beyond the head. The mild dissent: a few find it forward rather than laid-back, and it stops short of the pricier Valhalla's layering.
“an expansive soundstage that feels like a true bubble, with elements spread far apart.”
Edward Lau (owner), THIEAUDIO
“I've never had a pair make the music feel this open and layered; it feels like each part of the song exists in a different sections of space around your head and sometimes, the room.”
S0KKermom, r/iems
“Soundstage depth is quite good, while width is just above average.”
Hifitopia, HiFiTopia
Rated a strength alongside the stage — precise placement and clean separation that owners single out as a top pro. The one caveat: a couple of listeners find the image leans airy and 'diffuse' rather than thick and weighty, and a few TOTL rivals edge it on outright separation.
“Imaging is impressive, very clear separation between the instruments.”
Safe_Opinion_2167, r/iems
“Excellent soundstage and imaging”
Reddit (aggregated), RedditRecs
“the imaging offers nice separation and positioning, but errs a little bit on the side of “diffuse” over thick and weighty”
Stephen Kostas, Bloom Audio
Detail
Strong consensus · 8 srcThe clearest point of agreement, conceded even by the set's harshest critic: resolution and detail retrieval are excellent for the price, clean and consistent across the range. The one caveat is a double edge — that same revealing nature is unforgiving of poorly-mastered tracks.
“It’s undeniably an excellent IEM by almost every metric I look at.”
Fc-Construct, Headphones.com
“Resolution and detail reproduction are both really high and homogeneous across the spectrum.”
Hifitopia, HiFiTopia
“the MKIV delivers exceptional resolution — constant clarity, vivid detail retrieval”
Edward Lau (owner), THIEAUDIO
Fast and engaging, with quick transients and a low end that most call punchy and slam-capable — especially with the RUMBLE switch engaged. The dissent comes from standard mode's leaner mid-bass: a few feel it trades physical weight and slam for speed.
“the bass texture and slam is fantastic, best I've heard.”
Safe_Opinion_2167, r/iems
“the bass here feels lean with limited impact and slam”
Edward Lau (owner), THIEAUDIO
Comfort
Contested · 10 srcThe single most common practical complaint, and a genuine split. The shell is large and the nozzle thick (6.3 mm); many find it big-but-livable — ergonomic, and fine after a short break-in — while others find it too bulky to seal or wear for long, and it's the #1 con in the community aggregate. Fit is worth checking before you buy, especially with smaller ears.
Where it splits· split roughly even
Large but livable — a well-shaped shell that many wear for hours, sometimes after a short break-in.
“The Monarch MKIV is definitely on the bigger side, but the ergonomic shape makes it easier to live with.”
Nihal, Headfonics
Too big and chunky for some — a wide shell and thick nozzle that presses, unseals, or simply won't fit smaller ears.
“Bulky and uncomfortable for some users”
Reddit (aggregated), RedditRecs
A standout at the shell: CNC-machined T6 aluminum, sculpted like the flagship Valhalla, widely called some of the best hardware for the money. The gripes are about the accessories, not the earpieces — the modular 'Chocolate' cable draws complaints about its brown color scheme, and the flimsy carry case/puck is a repeated knock.
“the hardware on this IEM is some of the best for the money.”
Fc-Construct, Headphones.com
“My only complaint with this cable is that it doesn’t match the IEMs’ color scheme and feels a bit lackluster due to its brown color scheme.”
Nihal, Headfonics
“The felt covered cardboard puck of the MkIV is simply trash.”
Cockroach-Jones, r/iems
Isolation
Thin evidence · 2 srcLightly covered, but the sealed shell isolates well by IEM standards once you get a good tip seal, with no driver flex or pressure build-up reported.
“The Monarch MKIV performs well at isolation, blocking out a fair amount of ambient noise.”
Nihal, Headfonics
“I would say the tips are above average for isolation.”
Hifitopia, HiFiTopia
Genuinely split for a kilobuck flagship. Fans call it a technical over-achiever — punching above its $1,149 and a legitimate diminishing-returns endgame. Skeptics counter that any kilobuck is hard to justify, and that $120–300 sets now get you most of the way; the MKIV is also the first Monarch to raise the line's price.
Where it splits
Strong technical value for a kilobuck — a legitimate diminishing-returns endgame.45%
“you definitely don’t feel like you’re listening to an $1150 IEM.”
Hifitopia, HiFiTopia
Hard to justify at $1,149 — expensive, and much cheaper sets now get you most of the way.55%
“I can’t really call any of these IEMs “good value” - they’re all expensive.”
Fc-Construct, Headphones.com
