Fosi Audio IM4 vs Letshuoer S12 Ultra: which should you buy?

On aggregated review scores the Letshuoer S12 Ultra comes out ahead with a HearWiki score of 83. The full breakdown - sub-scores, specs and what reviewers actually said - is below.

Our pick: Letshuoer S12 Ultra - Outstanding overall at around $169.

Wired IEMs

Score breakdown

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

Letshuoer S12 Ultra leads on 3 of 4 measures.

Fosi Audio IM4
Letshuoer S12 Ultra

HearWiki score

Sound

7.4

8.6

Value

7.8

8.9

Price (USD)

$100

$170

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

Both shipped in 2025. These are 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.

IM42025
S12 Ultra2025

Specifications

IM4S12 Ultra

Type: Wired IEMs; Wired IEMs
Price (USD): $100; $170
HearWiki score: 72; 83
Released: 2025; 2025
Availability: Sold new; Sold new
Driver: 2× 10 mm dynamic; 1 planar magnetic
Driver type: dynamic; planar
Driver configuration: -; 1 planar magnetic
Driver size: 10 mm; 14.8 mm
Drivers per side: 2; 1
Impedance: 21 Ω; 16 Ω
Weight: 7 g; -
Connector: 2-pin 0.78 mm; -

Specification comparison of Fosi Audio IM4 vs Letshuoer S12 Ultra
Spec	Fosi Audio IM4	Letshuoer S12 Ultra
Type	Wired IEMs	Wired IEMs
Price (USD)	$100	$170
HearWiki score	72 / 100 Great	83 / 100 Outstanding
Released	2025	2025
Audio
Driver	2× 10 mm dynamic	1 planar magnetic
Driver type	dynamic	planar
Driver configuration	-	1 planar magnetic
Driver size	10 mm	14.8 mm
Drivers per side	2	1
Impedance	21 Ω	16 Ω
Design
Weight	7 g	-
Connector	2-pin 0.78 mm	-

What reviewers said

Fosi Audio IM4

The Fosi Audio IM4 is a wired, dual-dynamic-driver IEM that delivers a spacious, engaging sound with a focus on upper mids and treble detail. It suits acoustic and vocal-centric listening, though its tuning is more niche than universally neutral. With solid build quality, light weight, and strong value, it's a compelling budget option for those seeking a lively, open presentation.

Pro:Lightweight and comfortable fit
Pro:Spacious, open soundstage with good separation
Pro:Strong detail retrieval and resolution for the price

Con:Tuning is uneven for all-purpose use
Con:Metallic cymbal timbre at times
Con:Lower mids can sound slightly imbalanced

Letshuoer S12 Ultra

The Letshuoer S12 Ultra is a wired in-ear monitor that delivers Hi-Fi sound through a single 14.8mm planar magnetic driver housed in a lightweight aluminum-alloy shell. Aimed at music enthusiasts, it offers the signature planar-driver clarity and detail of the S12 series in a refreshed design, without any active noise cancellation or wireless features. Priced around $169, it's a straightforward, high-performance option for wired listening.

Pro:Detailed and fast planar magnetic sound
Pro:Lightweight and durable aluminum-alloy build
Pro:Accurate bass response with low distortion

Con:Requires a wired connection, no wireless freedom
Con:No active noise cancellation for noisy environments
Con:Open-back style may leak sound in quiet settings

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 Fosi Audio IM4 Letshuoer S12 Ultra