Sony IER-M9 vs THIEAUDIO Monarch MKIV: which should you buy?

On aggregated review scores the THIEAUDIO Monarch MKIV comes out ahead with a HearWiki score of 84. The full breakdown - sub-scores, specs and what reviewers actually said - is below.

Our pick: THIEAUDIO Monarch MKIV - Outstanding overall at around $1149.

Wired IEMs

Score breakdown

Each axis is a 0–10 blend of what reviewers scored, not a lab measurement.

THIEAUDIO Monarch MKIV leads on 3 of 4 measures.

Sony IER-M9
THIEAUDIO Monarch MKIV

HearWiki score

Sound

8.7

9.4

Value

7.4

7.6

Price (USD)

$970

$1,150

Generation & platform

The scores rank quality. This is the other question: is the newer one actually newer technology, or the same platform in a new shell?

Same generation

The THIEAUDIO Monarch MKIV is 7 years newer, but it is the same generation of hardware: nothing in the radio, the codecs or the noise cancelling separates them. Nothing separates them on convenience features either, so the choice comes down to tuning and price. For 7 years between them, that is a thin return - treat this as a restyle rather than a new platform.

IER-M92018
Monarch MKIV20257 yr newer

Specifications

IER-M9Monarch MKIV

Type: Wired IEMs; Wired IEMs
Price (USD): $970; $1,150
HearWiki score: 67; 84
Released: 2018; 2025
Availability: Discontinued; Sold new
Driver: 5BA; 2DD + 6BA + 2EST tribrid
Driver type: balanced-armature; tribrid
Driver configuration: 5BA; 2DD + 6BA + 2EST
Driver size: -; 8 mm
Drivers per side: 5; 10
Impedance: 20 Ω; -
Sensitivity: 103 dB/mW; -
Weight: 11 g; -
Detachable cable: Yes; -

Specification comparison of Sony IER-M9 vs THIEAUDIO Monarch MKIV
Spec	Sony IER-M9	THIEAUDIO Monarch MKIV
Type	Wired IEMs	Wired IEMs
Price (USD)	$970	$1,150
HearWiki score	67 / 100 Good	84 / 100 Outstanding
Released	2018	2025
Audio
Driver	5BA	2DD + 6BA + 2EST tribrid
Driver type	balanced-armature	tribrid
Driver configuration	5BA	2DD + 6BA + 2EST
Driver size	-	8 mm
Drivers per side	5	10
Impedance	20 Ω	-
Sensitivity	103 dB/mW	-
Design
Weight	11 g	-
Detachable cable	Yes	-

What reviewers said

Sony IER-M9

The Sony IER-M9 is a premium five-balanced-armature wired IEM that delivers a refined, reference-style sound with a warm and coherent character. It combines strong technical detail with a mature, balanced tuning that works well across genres, appealing to both monitoring professionals and casual listeners seeking a polished, realistic presentation. Its lightweight build and detachable cable add to its practical appeal at a high-end price point.

Pro:Detailed and resolving five-driver balanced-armature design
Pro:Warm, coherent, and well-balanced tuning with strong midrange
Pro:Lightweight 11g build with detachable cable

Con:High price around $973
Con:No active noise cancellation
Con:Requires a capable source due to 20-ohm impedance

THIEAUDIO Monarch MKIV

The Monarch MKIV is a flagship in-ear monitor built around a ten-driver tribrid configuration, blending dual 8mm dynamic drivers, six balanced armatures, and two electrostatic tweeters. It offers a studio-neutral sound signature with an additional switchable bass-boost mode for listeners who prefer a more impactful low end.

Pro:Reference-grade neutral tuning with excellent clarity
Pro:Versatile bass boost mode adds flexibility
Pro:Detailed and extended treble from electrostatic tweeters

Con:High price point limits accessibility
Con:Requires a capable source to perform at its best
Con:Large shell may not suit smaller ears

Summaries are AI-condensed and paraphrased from published reviews and specs - not original hands-on testing. More on our method.

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New comparison Sony IER-M9 THIEAUDIO Monarch MKIV