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 around the $100 mark that leans into an open, detailed sound with a focus on upper mids and treble. It's a comfortable, well-built option that shines with vocals and acoustic material, though its tuning may feel a bit uneven for those wanting a perfectly neutral all-rounder. Overall, it offers strong technical performance and value for its price, with a few tonal quirks to consider.

Pro:Spacious, open soundstage with good separation
Pro:Comfortable and solid build quality
Pro:Strong detail retrieval for the price

Con:Tonal balance can feel uneven, especially in lower mids
Con:Cymbal timbre can come across as metallic at times
Con:No modular plug system included

Letshuoer S12 Ultra

The Letshuoer S12 Ultra is a wired in-ear monitor built around a single 14.8mm planar magnetic driver housed in a lightweight aluminum shell. It delivers the signature planar sound of the S12 line—fast, detailed, and punchy—in a refreshed design aimed at hi-fi enthusiasts. With a low 16-ohm impedance, it pairs easily with most sources, though it lacks any active noise cancellation.

Pro:Fast, detailed planar sound with strong dynamics
Pro:Lightweight and sturdy aluminum-alloy build
Pro:Easy to drive thanks to low impedance

Con:No noise cancellation or isolation features
Con:Planar timbre may not suit all listeners
Con:Cable and accessories are basic for the price

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

Compare something else

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New comparison Fosi Audio IM4 Letshuoer S12 Ultra