64 Audio U4S 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.

64 Audio U4S
THIEAUDIO Monarch MKIV

HearWiki score

Sound

8.5

9.4

Value

6.6

7.6

Price (USD)

$1,100

$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 2 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.

U4S2023
Monarch MKIV20252 yr newer

Specifications

U4SMonarch MKIV

Type: Wired IEMs; Wired IEMs
Price (USD): $1,100; $1,150
HearWiki score: 73; 84
Released: 2023; 2025
Availability: Discontinued; Sold new
Driver: 1DD + 3BA hybrid; 2DD + 6BA + 2EST tribrid
Driver type: hybrid; tribrid
Driver configuration: 1DD + 3BA; 2DD + 6BA + 2EST
Driver size: -; 8 mm
Drivers per side: 4; 10
Impedance: 11 Ω; -
Sensitivity: 107 dB/mW; -
Active noise cancelling: No; -

Specification comparison of 64 Audio U4S vs THIEAUDIO Monarch MKIV
Spec	64 Audio U4S	THIEAUDIO Monarch MKIV
Type	Wired IEMs	Wired IEMs
Price (USD)	$1,100	$1,150
HearWiki score	73 / 100 Great	84 / 100 Outstanding
Released	2023	2025
Audio
Driver	1DD + 3BA hybrid	2DD + 6BA + 2EST tribrid
Driver type	hybrid	tribrid
Driver configuration	1DD + 3BA	2DD + 6BA + 2EST
Driver size	-	8 mm
Drivers per side	4	10
Impedance	11 Ω	-
Sensitivity	107 dB/mW	-
Features
Active noise cancelling	No	-

What reviewers said

64 Audio U4S

The 64 Audio U4S is a premium hybrid universal IEM that blends a dynamic driver with three balanced armatures to deliver a lively, well-rounded sound. Its tuning strikes a balance between engaging bass and clear treble, offering solid resolution and layering for a versatile listening experience. With an 11-ohm impedance and 107 dB sensitivity, it is easy to drive from most sources.

Pro:Energetic and punchy bass response
Pro:Smooth lower mids with fast treble
Pro:Solid technical performance with good layering

Con:Lower mids can feel slightly recessed
Con:Price may be steep for some buyers
Con:No included cable options for balanced use

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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