In-Ear MonitorOverreview

THIEAUDIO Monarch MKIII

The Monarch that traded the MKII's midrange for slam and air — and split its own audience doing it.

41 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 electrostatic tweeters) and the Monarch generation built for bass. Sources agree on deep, textured, physical low end; on detail retrieval that ranks with the class at the price; on a wide stage; on a good modular cable and well-matched channels; on good passive isolation; and that it is easy to drive. Where opinion splits is on character. Most hear a deliberately coloured U/V-shape — more bass and more top end than the MKII — and divide on whether that is engaging or unnatural. The midrange, once the line's calling card, is now contested: clean and accurate to one camp, leaner and less natural than the MKII's to another, including several of the best-known ranking lists. The treble divides almost exactly in half between airy and fatiguing — and the measurements show why: the presence region sits below the usual target while the top octave sits far above it, and tips and insertion move that top octave a lot. Dynamics split between punchy and big-but-soft. Fit is the most common practical complaint: the shell is large and the nozzle wide, and a majority of the weighted voices say it won't suit smaller ears. Most still call it good value at the price, with a minority pointing at much cheaper sets.

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 for the mids, two Knowles DWFK 31785 units for the upper range and Sonion electrostatic tweeters, on a 4-way passive crossover) in a 3D-printed resin shell. Not the Monarch MKII, which still sells 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 switch and $1,149. Custom shell and faceplate designs cost $1,099 or $1,149. THIEAUDIO's page rates it 20 Ω and Linsoul's 18 Ω.

The THIEAUDIO Monarch MKIII is the $999 third generation of the IEM line that made ThieAudio — the in-house brand of retailer Linsoul — a fixture of enthusiast shortlists. It packs ten drivers per side into a resin shell: two 10 mm dynamic drivers working together in an isobaric IMPACT² subwoofer module, six balanced armatures across the mids and upper range, and two Sonion electrostatic tweeters for the very top, on a 4-way passive crossover. The second dynamic driver is the headline change, aimed at the complaint that followed both earlier Monarchs: not enough mid-bass.

It worked, and that is precisely the argument. The MKII was prized for its balance and its midrange; the MKIII adds body down low and energy up top, and reviewers have argued ever since about whether that made it better or simply different. Launch reviews were near-uniformly warm, while several of the hobby's most-read ranking lists — and a steady stream of owners who went back to the MKII — are markedly cooler. The measurements make the fight stranger still: one lab scores the treble as slightly recessed and the whole set as warm, while a large share of listeners call the top end fatiguing.

A good fit for

  • Listeners who want rumble and weight without giving up resolution — the bass and the technical package are the least-disputed strengths
  • Pop, EDM, hip-hop and rock listeners who like a U-shaped flagship with energy at both ends
  • Treble lovers who find typical IEMs short of air
  • People with average or larger ears who can take a big shell and a wide nozzle
  • Buyers who care how their IEMs look — custom shells and faceplates are available to order
  • Anyone driving IEMs from a low-impedance 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 wide, and fit is the most common complaint (demo first if you can)
  • You loved the Monarch MKII's midrange and vocals — the MKIII deliberately traded some of that for bass and treble
  • You're treble-sensitive or listen loud — the lifted top octave is exactly what its critics single out
  • You want the sharpest, most gripping transient punch at the price — the bass has weight but rounds its edges
  • Your source has a high output impedance — it changes this set's bass and treble noticeably
  • You want a forgiving set for poor recordings — this one is revealing enough to expose weak masters

The reviewer consensus

Agreement &
disagreement.

5 / 12topics divide opinion
isolationbasssoundstageimagingdetailbuildvaluetonalitymidstrebledynamicscomfort
1 Strong agreement6 Mostly agree5 Divided opinions

Common ground7

  • Deep, textured, physical bass — the dual isobaric dynamic drivers fixed the mid-bass complaint that followed both earlier Monarchs.
  • Detail retrieval that ranks with the class at the price; even owners who returned it concede the resolution.
  • A wide, tall stage with precise placement and clean separation in dense mixes.

Points of contention5

  • Tonality: a balanced all-rounder vs a deliberately coloured U/V-shape — and, within that, fun vs unnatural.
  • Mids: flat, accurate and resolving vs leaner and less natural than the MKII's, with the vocal magic gone.
  • Treble: airy and non-fatiguing vs an exaggerated top octave that turns tiring — split almost exactly in half, and strongly tip-dependent.

A closer listen.

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

Tonality

Leans positiveDivided opinions
Reviewer sentiment16 supporting sources
CriticalNeutralPositive

Band: opinion spread · Dot: weighted average

Sources split on what kind of IEM this is. A minority hear a balanced, versatile tuning that keeps the Monarch's monitor DNA and simply fills in the low end. Most hear a deliberately coloured U- or V-shape — more bass and more upper treble than the MKII — and then divide again on whether that colour is fun or unnatural: Crinacle prefers the MKII on taste, and two headphones.com ranking lists score the MKIII 4/10 for exactly this. If you specifically want the MKII's balance, the MKIII is not it.

Measured

Across 23 independent squig.link rigs (normalised at 500 Hz) the MKIII matches the Harman IE 2019 target's sub-bass almost exactly (+8.8 vs +9.0 dB at 20 Hz), runs about 1 dB over it at 100 Hz, sits roughly 2–3 dB under it from 3 to 6.5 kHz, and runs 5–8 dB over it at 13–16 kHz. RTINGS scores the bass "Emphasized (3 dB)", the treble "Balanced (-1 dB)" and the sound signature "Warm". On the 16 rigs that measured both generations, the MKIII adds a median ~1 dB at 80–150 Hz and ~2 dB at 4–6.5 kHz over the MKII.

Where it splits
A balanced, versatile all-rounder — the Monarch's tuning with the missing low end finally filled in.34%

“Very little of the Monarch MKIII presentation is what I would consider ‘out of whack’.”

Marcus, Headfonics
A deliberately coloured U/V-shape — more bass and more treble than the MKII; exciting to some, unnatural to others.66%

“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

The hardware

Specifications.

Checked

Design

Type
In-ear monitor
Drivers
2 × 10 mm dynamic (IMPACT² composite DD) + 6 × balanced armature (Knowles DWFK 31785 ×2, Sonion 28UAP ×1) + 2 × electrostatic (Sonion EST)2DD + 6BA + 2EST
Housing
3D-printed medical-grade resin

Electrical

Impedance
20 Ω
Frequency response
20 Hz – 80 kHz

Connection

Cable
Detachable, 1.2 m
Connector
0.78 mm 2-pin
Plugs supplied
2.5 mm balanced, 3.5 mm, 4.4 mm balancedmodular

Manufacturer-published figures, not measurements · from thieaudio.com, linsoul.com.

Follow the evidence

Sources 41

1–6 of 41 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 October 2026. The MKIII arrived in 2023 and has since been joined by the Monarch MKIV, so some of the early enthusiasm was written when the field looked different.

  2. Three Monarchs share the name and two still sell at the same time — the MKII at the same $999 with a leaner tuning, and the MKIV at $1,149. Check which generation a listing or review actually means.

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