By aspect — in detail
The most consistently praised region: deep, fast, textured and controlled, a sub-bass-first shelf that reaches lower than the S12 Pro without bleeding into the mids. The caveats are about quantity and character rather than quality — mid-bass slam is lighter than a dynamic driver's, a few hear it as slightly boomy on dense mixes, and a small minority (mostly on weaker seals or sources) hear it as lean.
“The bass is stunning. It’s powerful but not overpowering; it’s detailed and textured.”
Chris, The Headphoneer
“In real music, the result is a very compact bass, with quite a punch, dry, tight, very fast and with hardly any decay.”
cqtek, HiEndPortable
“I think all of these have a little bit too much bass for my personal taste, but it's fun.”
Super* Review (video transcript)
“I think the number one issue that some folks will have with the S12 Ultra is that the mid-bass doesn’t have that forward and profuse slam that some may like.”
Chris Love, Mobileaudiophile
“Excellent IEMs for its price. Clear mids and highs. Bass are on the weaker side.”
Amazon customer (in the listing's review highlights)
Measured
Twelve-rig average, 500 Hz-normalised: +11.8 dB at 20 Hz (sd 0.9), +10.4 at 40 Hz, +8.7 at 60 Hz, +6.0 at 100 Hz, +2.4 at 200 Hz — 2.8 dB above Harman IE 2019 at 20 Hz and 1.5–1.9 dB above it from 60 to 250 Hz. Versus the S12 Pro on seven shared rigs it has +2.2 dB at 20 Hz and about 1 dB less from 100 to 250 Hz: more sub-bass, slightly less mid-bass.
⚠ vs. listeners — The shelf is sub-bass-first on every rig, yet a few listeners describe punch without rumble or a lean bottom end; with a bass region this consistent across rigs, a shallow seat or leaky seal is the likelier explanation than unit variation.
Sources split. The majority hears the biggest improvement in the series — warm, full, organic vocals with no planar metallic edge and no shout, the one region the old S12s got wrong. A smaller but forceful camp, including two of the most critical reviewers, hears the same tuning as a scoop: vocals a step back, thin or hollow, lacking presence and emotional pull, with a 1.5 kHz bite that shows on bass-light tracks.
Measured
The ear-gain peak arrives early and low: +8.1 dB at 2 kHz (Harman +7.2) then +5.2 at 3 kHz and +4.8 at 3.5 kHz, 5–6 dB under the Harman peak, while 1–1.5 kHz sits 0.6–2.1 dB above the target. Across rigs the 2–3.5 kHz region varies by only 0.5–0.7 dB, so this is the tuning, not a rig or unit effect.
⚠ vs. listeners — Both camps are describing the same shape. The missing 3–4 kHz is what the majority hears as warmth and ease and the minority hears as absent presence; the 1.5–2 kHz bump is the 'bite' several reviewers pin on vocals when nothing below masks it.
Where it splits
organic, full and natural — the most improved region84%
“Midrange has great timbre, no planar metallic edge, nice presence”
Chris Love, Mobileaudiophile
recessed, thin and lacking presence — vocals lose their connection16%
“Being devoid of harshness leads to no presence leaving the tuning in darkness.”
json's blog
Sources split three ways. The large majority hears the fix the series needed — smooth, sibilance-free, still detailed, with the S12 Pro's sharpness gone. One minority hears it as over-corrected: less extension and energy than a planar should have, air rolled off, nothing for treble lovers. A second, smaller minority hears the opposite — a still-boosted 5–8 kHz region that reads hot, spicy or grainy on bright recordings.
Measured
+7.0 dB at 5 kHz, +6.7 at 6 kHz and +8.4 at 8 kHz (sd 1.9) relative to 500 Hz — about 3 dB over Harman at 8 kHz — then +0.6 at 10 kHz, a −7 dB notch at 12 kHz and a rise again at 15 kHz. Against the S12 Pro it is −2.4 dB at 8 kHz and −4.2 dB at 12 kHz. Insertion depth moves 6–10 kHz by ±3–5 dB while everything below 5 kHz stays within 1 dB.
⚠ vs. listeners — The 8 kHz peak is real on all twelve rigs, yet most listeners call the treble smooth; the two dissenting camps are reading different parts of the same curve — the 12 kHz notch as missing air, the 5–8 kHz plateau as heat — and insertion depth alone can swing that region by several decibels.
Where it splits
smooth and refined — the S12 finally without the zing86%
“It does have kind of that forward aggressive treble in the frequency response graph. I'm not hearing it like that.”
Super* Review (video transcript)
too polite — extension and energy went with the sharpness8%
“I will be straight forward here, coming from the S12 pro, Ultra feels like it’s lacking with both extension and energy.”
Suman Sourav Meher, The Headphone List
still hot — a boosted, uneven top end that grates on the treble-sensitive6%
“Not even the immensely boosted treble could save this, and I do mean genuinely boosted.”
json's blog
Tonality
Moderate · 57 srcDescribed almost unanimously as warm-neutral to mild-V: a sub-bass lift, a relaxed upper midrange and a softened top, musical over analytical. Most call it the most balanced and coherent S12; the recurring reservation is that it plays safe — 'a great IEM or a boring one' depending on taste — and a small minority hears it as thin, uneven or simply too deviated to enjoy.
“the sound is what I’d call a warm/neutral sounding set with a tilt towards the warm.”
Chris Love, Mobileaudiophile
“Look from your perspective, it’s either a great IEM or an boring one depending on preferences, nothing in-between.”
Suman Sourav Meher, The Headphone List
“And I'll admit that most people are going to prefer ultra.”
Paul Wasabii (video transcript)
“But overall, it is too sharp, too thin, and too uneven for me.”
u/KAC-SK, r/iems (purchased unit)
Measured
Within ±0.8 dB of the S12 2024 from 20 Hz to 5 kHz on seven shared rigs (−1.9 dB at 6 kHz, −2.4 at 15 kHz); versus the original S12 on nine rigs, +2.8 dB at 20 Hz, −2.9 at 3 kHz and −4.8 at 10 kHz. Against Harman IE 2019: bass +2–3 dB, 3–4 kHz −5 to −6 dB, 8 kHz +3.4 dB.
Soundstage
Contested · 38 srcSources split evenly. One half hears a stage that is wide for an IEM with real layering and depth for a planar; the other hears it as intimate, in-the-head and shallow — wide left-right but with height and front-to-back depth curtailed, and a clear step down from the S12 2024. Nearly a third of the sources sit in between ('average, not congested').
Where it splits· split roughly even
large for an IEM, with layering and depth
“The soundstage feels large for an IEM. Instrument separation is great, and the imaging excellent.”
Chris, The Headphoneer
intimate and in-the-head — width without height or depth
“It's close. It's just too in your head, too inward, not as open sounding.”
Paul Wasabii (video transcript)
Generally rated a strength: precise left-right placement and good separation for the price, with planar speed keeping busy passages clean. The dissent comes from the reviewers who hear the stage as compressed — everything gathering in the centre — and from one owner for whom layering fell apart on dense tracks.
“Imaging on the other hand is actually very nice.”
Chris Love, Mobileaudiophile
“the S12 ultra instead with its wider stage, great instrument separation and imaging restores the same sunken valley into its past glory.”
monkonomics, Head-Fi
“Strong instrument separation and layering”
George Dobrescu, Audiophile-Heaven
“Everything felt presented in the center and more in my head.”
u/KAC-SK, r/iems (purchased unit)
Resolution is rated very good for $169 and, by several, competitive with pricier dynamic and hybrid sets — but nearly everyone adds 'for the tuning': the softened treble trades some micro-detail and transparency for musicality, and the S12 2024 and brighter rivals resolve more. A minority calls it merely average for the price.
“Detail level is excellent at this price point.”
Chris, The Headphoneer
“The resolution is very good and I would argue S12 Ultra can compete with DD or BA iems costing many times more.”
Leonarfd, Head-Fi
“Resolution and overall definitions are above average but falls behind similarly priced IEMs.”
Suman Sourav Meher, The Headphone List
Dynamics
Moderate · 25 srcPlanar-fast transients and a punchy, physical low end, but macro-dynamics are 'smooth, not explosive' and a few hear the set as flatter and less dynamic than the S12 2024. Almost every source ties this to power: it reaches volume easily from the bundled dongle, yet the bass tightens, the stage grows and the treble comes forward on a stronger, cleaner source — and reviewers disagree on whether the dongle is 'a great job' or 'disappointing'.
“One thing which becomes apparent very quickly is the dynamics of your session when listening to the S12 Ultra with a more powerful source.”
Chris Love, Mobileaudiophile
“It does sound smoother, but to me, it also sounds smaller. It does sound flatter. It sounds less transparent, less dynamic”
Paul Wasabii (video transcript)
“The S12 Ultra is also noticeably easier to drive than the S12 Pro, and the included DT01 USB dongle does a great job.”
Chris, The Headphoneer
“Pairing it with it’s own dongle though is disappointing.”
Suman Sourav Meher, The Headphone List
One of the strongest points of agreement: a small, light, flush-fitting metal shell that even the harshest critics single out, with a good seal from either stock tip family. The exceptions are large ears wanting a longer nozzle, a couple of owners who find the shell heavy or cold, and an occasional click on insertion that owners diagnose as driver flex.
“The shell is light, small, and comfortable. Fit was easy for me, and I had no real complaints with pressure or seal.”
u/KAC-SK, r/iems (purchased unit)
“This series has always fit my ears well.”
Chris Love, Mobileaudiophile
“since I have large ears the S12 models do not work that well for me and I would have preferred longer nozzles.”
Leonarfd, Head-Fi
Near-unanimous praise for the CNC-aluminium shells, the colour-matched 392-core modular cable with screw-locked plugs, the puck case and the bundled dongle — the best accessory haul in the series. The recurring complaints are stiff 2-pin sockets that make cable swaps risky, a thinner cable than the S12 2024's, and isolated reports of driver flex.
“Build quality of this IEM is bulletproof.”
Suman Sourav Meher, The Headphone List
“This definitely is one of the best looking cables available with an IEM priced under $200.”
Suman Sourav Meher, The Headphone List
“The 2-pin connectors are extremely stiff. Cable swapping feels unnecessarily risky, and there’s a real chance of bending cable pins if you’re not very careful.”
Nealz, Head-Fi
Isolation
Moderate · 6 srcRated good-to-sufficient for a vented planar — one reviewer puts it around 20 dB — and dependent on tips and seal; fine for everyday use, not a commuter's isolator.
“S12 Ultra has a natural passive noise isolation of around 20 dB, and with music playing, even at low volumes, you shouldn’t notice the background noise.”
George Dobrescu, Audiophile-Heaven
“Passive isolation is sufficient for everyday use.”
Kagrra, Head-Fi
Widely called the S12 to buy and one of the best planar packages under $200 — the ranking aggregate, the Reddit sentiment tally and most critics agree, and several owners cite it against far pricier sets. The dissent is from the two most critical reviewers (one bought his) and from those who find cheaper planars or the S12 2024 the smarter buy.
“The Letshuoer S12 Ultra is possibly the IEMS of this type with the best value for money and sound quality.”
cqtek, HiEndPortable
“even at full price, which I think that's what it is, it still sounds more coherent, more resolved, more natural than most $200 hybrids”
Paul Wasabii (video transcript)
“I just got the s12 ultra used for $120 and compared it to my $1000 monarch mk4 and honestly it’s tough to justify keeping the monarch.”
u/Alert-Crab-2660, r/iems (via RedditRecs)
“That said, I don’t think it sounds that great at all, just fine.”
json's blog
