In-Ear MonitorOverreview

THIEAUDIO Monarch MKIII

The Monarch that traded monitor neutrality for slam and air — and split its own audience doing it.

76/ 100
Review score
14 sourcesUpdated
$999Typical US price

Score aggregates reviewer opinions across topics.

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THIEAUDIO Monarch MKIII

The short version

What to know.

A $999 tribrid IEM with ten drivers per side (two 10 mm isobaric dynamic drivers, six balanced armatures and two Sonion electrostatic tweeters, 4-way crossover) and the generation that gave the Monarch line real bass. Reviewers agree firmly on the core: a flat, natural, well-resolved midrange that is the line's signature strength, detail retrieval that ranks with anything at the price, a deep and genuinely extended low end, a wide three-dimensional stage, excellent build with a good modular cable, and measured channel matching that holds across the whole audible band. Where opinion splits is on the set's character rather than its competence. Sources disagree on what kind of IEM it is — a balanced monitor-style all-rounder or a deliberately coloured, bassier U/V-shape that departs from the MKII's neutrality; on the treble, which one camp hears as airy and non-fatiguing and another as exaggerated ultra-treble zing (the measurements complicate this, since one lab reads the treble as balanced-to-slightly-recessed and the set overall as warm); on dynamics, where the bass is either genuinely punchy or big-but-soft on transients; on comfort, the single most common practical complaint, since the shell is flagship-sized with a nozzle over 6 mm; and on value, strong at the price to most reviewers but hard to justify to a vocal minority. It is also notably better received by the press than by the community — enthusiast impressions run only about half positive. Tips, a clean rather than warm source, and honest self-assessment about ear size are how most owners settle it.

About this product

The 2023 third-generation Monarch — a 2DD + 6BA + 2EST tribrid (two 10 mm composite-diaphragm dynamic drivers in THIEAUDIO's isobaric IMPACT² module, a Sonion 28UAP dual BA for the mids, two Knowles DWFK 31785 dual BAs for the mid-highs, and two Sonion electrostatic tweeters, on a 4-way passive crossover) in a medical-grade resin shell. Not the 9-driver Monarch MKII, which sold alongside it at the same $999 with a leaner, more neutral tuning, and not the 2025 Monarch MKIV, which moved to a metal shell, a STANDARD/RUMBLE tuning switch and $1,149. Six shell colours and 14–16 faceplates are available made-to-order for roughly $50–150 more. THIEAUDIO's own page rates it 20 Ω and Linsoul's rates it 18 Ω; both agree on 99 dB @ 1 kHz.

The THIEAUDIO Monarch MKIII is the $999 third generation of the IEM line that made ThieAudio — the in-house brand of retailer Linsoul — a household name among enthusiasts. It packs ten drivers per side into a resin shell: two 10 mm dynamic drivers arranged face-to-face in an isobaric IMPACT² subwoofer module, six balanced armatures across the mids and mid-highs, and two Sonion electrostatic tweeters for the very top, all on a 4-way passive crossover. The second dynamic driver is the headline change, and it exists to answer the one complaint that followed both earlier Monarchs: not enough mid-bass.

It worked, and that is precisely the argument. The original and the MKII were prized as studio-monitor-ish reference sets; the MKIII adds a roughly 9 dB bass shelf and a lifted ultra-treble, and reviewers have been arguing ever since about whether that made it better or simply different. Professional reviews were near-uniformly warm — 8.9s and 88%s and gold badges — while the enthusiast community has been markedly cooler, with only about half of Reddit impressions landing positive. The measurements make the fight stranger still: one lab scores the treble as balanced and the whole set as warm, even warning it can sound dull, while a large share of listeners complain it is too hot.

A good fit for

  • Listeners who want resolution, air and a wide stage — the technical package is the strongest part of the set
  • Vocal and acoustic-instrument listeners, since the flat, natural midrange is the least-disputed strength
  • Sub-bass lovers who want real rumble and weight without the low end smearing into the mids
  • People with average or larger ears who can comfortably take a flagship-sized shell and a 6 mm-plus nozzle
  • Buyers who care how their IEMs look — six shells and 14–16 faceplates, made to order
  • Anyone driving IEMs from a phone dongle or DAP rather than a desktop stack

Think twice if

  • You have smaller ears or want all-day comfort — the shell is large and the nozzle thick, and fit is the most common complaint (demo first if you can)
  • You're treble-sensitive or listen loud — the lifted ultra-treble is exactly what its critics single out
  • You specifically want the Monarch MKII's leaner, more neutral balance — the MKIII deliberately moved away from it
  • You want the sharpest, most gripping transient punch at the price — the bass has weight but rounds its edges
  • You're price-sensitive — a real minority think much cheaper sets get most of the way, and the community is only about half positive
  • You want a warm, forgiving set for poor recordings — this one is revealing enough to expose weak masters

The reviewer consensus

Agreement &
disagreement.

5 / 12topics divide opinion
midsdetailbasssoundstageimagingbuildisolationtonalitytrebledynamicscomfortvalue
2 Strong agreement5 Mostly agree5 Divided opinions

Common ground7

  • A flat, natural, highly resolving midrange — the Monarch line's signature strength, and the thing the MKIII is least argued about.
  • Detail retrieval that ranks with the best at the price; even the reviewers most critical of the tuning concede it.
  • Deep, extended bass with real physical weight — the dual isobaric dynamic drivers fixed the complaint that followed both earlier Monarchs.

Points of contention5

  • Tonality: a balanced monitor-style all-rounder vs a deliberately coloured, bassier U/V-shape that departs from the MKII's neutrality.
  • Treble: airy, extended and non-fatiguing vs an exaggerated ultra-treble peak that manufactures detail and turns harsh — and the measurements don't settle it.
  • Dynamics: genuinely punchy and fast vs big-but-soft, with the mid-bass body rounding off transients.

A closer listen.

12 topics · 5 divided
Left: criticalRight: positiveTighter lines: more agreement

Tonality

Leans positiveDivided opinions
Reviewer sentiment10 supporting sources
CriticalNeutralPositive

Band: opinion spread · Dot: weighted average

Sources 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
Link to this topic

Follow the evidence

Sources 14

1–6 of 14 sources

Read with context

Limitations & method.

As of

What to keep in mind 8

  1. This is a read of where opinion sits as of August 2026. The MKIII arrived in 2023 and has since been joined by the Monarch MKIV, so some of the enthusiasm here was written when the field looked different.

  2. Three Monarchs share the name — the MKII sold alongside this one at the same $999 with a leaner tuning, and the 2025 MKIV is a different set again. Check which generation a listing or review actually means.

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