By aspect — in detail
Sources split on the same shelf. The large majority — most written reviews, nearly every Head-Fi and Reddit owner, and the video reviewers — hear a punchy, textured mid-bass with more control than the graph suggests and note that it is mid- and upper-bass, not sub-bass, that is boosted. A smaller but heavier-hitting camp, led by the measurement-minded ranking critics, hears the same shelf as bloom that runs into the lower mids. Both agree the sub-bass is only moderate.
Measured
Twenty-six IEC-711-class rigs agree to within about 1 dB below 300 Hz: relative to 500 Hz the shelf sits at +7.7 dB (20 Hz), +8.5 dB (40–60 Hz), +7.4 dB (100 Hz), and is still +4.5 dB at 200 Hz and +2.1 dB at 300 Hz. Against Harman IE 2019 that is 1 dB less at 20 Hz but +3 dB at 100 Hz and +4 dB from 150 to 250 Hz — a mid-bass hump, not a sub-bass shelf. Switch 1 lifts the whole band below 1 kHz by a flat +2.4 dB and nothing else; the 5128 rig reads the same shape.
⚠ vs. listeners — The graphs settle what is there, not how it lands: the +4 dB at 150–250 Hz is the weight the 'controlled' camp praises and the 'bloom' the critics object to. Tips and insertion depth move this region by under half a decibel on listener's rig, so the split is not a seal artefact; a high-impedance source (a phone, a Bluetooth adapter) does tilt it darker by 2–4 dB, which is where some of the 'muddy out of the box' reports come from.
Where it splits
big, punchy and better controlled than the graph suggests81%
“However, due to the clarity and the way the IEMs handles these notes, they are not overly bloated or muddy.”
SenyorC, Acho Reviews
over-extended into the low mids — bloom that reads as mud19%
“Overly extended bass that bleeds into the mid-range (very warm).”
Nymz, via IEMRanking
Sources split almost evenly. One camp hears a lush, natural, slightly warm midrange with well-judged upper mids that never shout — several call it the quiet strength of the set. The other hears vocals recessed, veiled or fuzzy behind the mid-bass, with female voices paying more than male. Flipping switch 1 down or switch 2 up moves listeners between the two camps more than any other variable.
Measured
Ear-gain peak of +7.0 dB over 500 Hz at 2.5 kHz across the rigs (Harman IE 2019: about +12 dB at 3–3.5 kHz), with 200–300 Hz running 2.5–4 dB above target and 2–4 kHz running 3–7.6 dB below it. Switch 2 adds +2.0–2.3 dB at 1.5–2 kHz and +1.5 dB at 2.5–3 kHz, nothing above 4.5 kHz; switch 1 off raises the relative ear gain by the same 2.4 dB it removes from the bass, so position 01 reads +9.5 dB where stock reads +7.0.
Where it splits
lush, natural and well-judged — the quiet strength47%
“But, beyond what is visible in the curves, the Quartets have completely convinced me in the mid-range.”
cqtek, Hi End Portable
Sources split three ways. The largest camp calls the top smooth, safe and non-fatiguing — treble-sensitive listeners' territory. A second camp calls the same top dark, muted and short of air, and names it the set's weak point. A third hears an uneven top with a peak around 8 kHz that spoils some tracks, especially with switch 2 off. Nobody calls it bright except one outlier review.
Measured
A dip to +0.6 dB at 4.5 kHz (about 6 dB under the ear-gain peak), +3.6 dB at 5 kHz, near-zero at 6–7 kHz, then +8.3 dB at 8 kHz on the 711 rigs — with an across-rig spread of 3.4 to 13.6 dB — and −2.5 dB at 10 kHz, −4.2 at 12 kHz. The 5128 rig shows no dominant 8 kHz peak (3.5 dB below its ear-gain peak). Switch 2 on takes about 1 dB off 7–8 kHz; tips and insertion depth move 7–12 kHz by up to ±6 dB and nothing below 5 kHz.
⚠ vs. listeners — All three camps are consistent with the same curve. 'Smooth' and 'dark' are the 4.5–7 kHz trough and the falling response above 9 kHz described from two reference points; the 'spike' camp is hearing the 8 kHz region, which the 711 couplers exaggerate — two reviewers who measured it themselves call it a coupler artefact and still report hearing it — and which moves with tips and seat more than anything else on this set.
Where it splits
smooth, soft and fatigue-free54%
“For my preferences, the treble is soft enough to shine where it needs to and then gets out the way.”
Guy Lerner, The Headphone List
dark and muted — the set's weak point25%
“The upper-mids and treble do sound a tad dark, and even compressed at times.”
Antdroid, Audio Discourse
uneven — peaks and dips, an 8 kHz spike on some tracks21%
“Moving into the upper ranges, there are a few peaks and dips that can sometimes interact in the wrong way with certain tracks and just in the right way with others.”
SenyorC, Acho Reviews
Tonality
Contested · 52 srcEveryone agrees on the shape — warm, bass-first, a mild V or L that no switch position turns neutral — and splits on the verdict. The larger camp calls it a coherent, fun, musical tuning that is more balanced than the marketing implies; a smaller camp of measurement-minded critics and later owners calls it too dark and coloured, a tuning the market has moved past.
Measured
Bass shelf about 1.5 dB above the ear-gain peak where Harman IE 2019 puts it 3 dB below — a 4.5 dB warmer tilt — plus the 200–300 Hz excess. The four switch positions span only 2.5 dB of bass-to-treble contrast and 3.5 dB at 1.5 kHz; the most neutral (01) still sits about 2.5 dB warmer than Harman in contrast terms. At a 15 Ω source the treble loses a further 1.5–3 dB relative to the bass, at 30 Ω about 4 dB.
Where it splits
a fun, coherent warm tuning — more balanced than 'basshead' suggests76%
“I’m not sure if all the talk of the funky dual-DD configuration got me primed for a ‘basshead’ IEM, but basshead Quartet is not.”
Guy Lerner, The Headphone List
Soundstage
Contested · 35 srcSources split: the larger camp hears an average-to-intimate stage — in-your-head, flat in depth, crowded on busy tracks — often blaming the bass for filling the space; a smaller camp, including two of the most careful listeners, hears a moderately wide stage with good depth. Several note it opens up with switch 1 off.
Where it splits
moderately wide with real depth40%
“The soundstage on the Quartet is moderately wide for an IEM, with good depth and layering.”
jeromeoflaherty, Head-Fi
average to intimate — flat, in-your-head60%
“Staging is neither too wide or tall, but also never congested, if a bit flat and lacking in depth.”
Guy Lerner, The Headphone List
Imaging
Contested · 28 srcSources split, largely along the music-versus-gaming line. Most music listeners find placement precise and separation decent for the price — one calls it among the best under $200. Gamers and the ranking critics disagree: layering is vague, busy passages blur, and footsteps get buried under gunfire compared with brighter rivals.
Measured
Channel matching is within about 1 dB below 5 kHz on most two-channel rigs; nothing in the data speaks to imaging beyond that.
Where it splits
precise placement, decent separation for the money68%
“There's not a lot of smearing of instrument notes across a band, and tracks with panning are still generally wide and pinpointable.”
Antdroid, Audio Discourse
vague layering — not the gaming set its shape suggests32%
“Depth is felt, but it is not stratified in a well-defined way, the planes are not individualised and there is a slight blending in this aspect.”
cqtek, Hi End Portable
Sources lean clearly negative, with a real minority dissent. Most call resolution average for $109 or below it — 'lo-fi', 'smeared', 'not a detail puppy', 'lack of resolution' — and several say the tuning masks what the drivers can do. A smaller camp hears surprising detail retrieval, mostly in the bass and lower mids.
Measured
Distortion measured well below 1 % at over 90 dB SPL on jeromeoflaherty's rig — the drivers are clean; the resolution complaints track the 4.5–7 kHz trough and the 2–4 kHz deficit rather than any nonlinearity.
Where it splits
more resolving than a bass set has any right to be27%
“But not only that, there is clarity, definition, resolution and dynamics.”
cqtek, Hi End Portable
average at best — the tuning trades clarity for warmth73%
“This is not a detail puppy, let alone monster, but conversely, if you’re looking for a laid-back listen with a warm and inviting tonality, that could be a good thing.”
Guy Lerner, The Headphone List
Dynamics
Strong consensus · 19 srcBroad agreement: the isobaric pair punches. Kick drums, bass lines and macro-dynamic swings are repeatedly singled out as livelier than the price predicts, even by reviewers who dislike the tuning. The only reservations are about decay — a few hear the bass switch slowing it.
“I do find it surprisingly more dynamic and punchy that I would have guessed at the $109 range though.”
Antdroid, Audio Discourse
“The kick drum thumps with palpable physicality, while the groovy bass line receives its deserved affection.”
David Becker, Prime Audio
Near-universal praise for a very light (about 4 g) semi-custom resin shell that stays put and wears for hours, with the caveat that it is medium-large: a few reviewers report a hotspot at the concha wing, and small ears may struggle. Owners on Amazon rate comfort well and fit less well, mostly over stock tips.
“The comfort is also excellent, as I can wear the Quartet for hours without any fatigue or discomfort.”
Meldrick, Headfonics
“These fit snugly to my ear because of the fit but these do tend to create hotspots”
Berry108, Head-Fi
Reviewers rate the one-piece resin shell and its finish far above the price; the thin stock cable and the tiny recessed switches (no tool in early boxes) draw the complaints. Owners add a durability tail the reviewers do not see: on Amazon every durability mention is negative, cable quality runs four-to-one negative, and Linsoul's own reviews include a dead switch and a dead side.
“Moreover, the build quality and finishing on this IEM is as good as any IEM I’ve seen, and by any I mean IEMs that cost north of $1,000 as well.”
Guy Lerner, The Headphone List
“durability is poor with reports of cracking and constant popping off”
Amazon, 'Customers say' review summary
Isolation
Moderate · 16 srcMostly rated good to excellent — several call it the best-isolating set they own — with two credible dissents calling it below average. The measurement explains both: it blocks the voice band unusually hard and low-frequency rumble unusually little.
“In fact, the Quartets are the best-isolating IEMs I’ve tried thus far.”
Meldrick, Headfonics
“Isolation is below average, though the Quartet is still usable outdoors.”
baskingshark, Head-Fi
Measured
On Acho Reviews' isolation rig the Quartet attenuates −7.7 dB at 125 Hz, −10.5 dB at 500 Hz, −27.5 dB at 1 kHz and −54 to −58 dB from 2 to 8 kHz. On the same rig the Salnotes Zero reads −11.4 / −23.0 / −30.0 / −43.0 and the Kiwi Cadenza −9.2 / −19.5 / −20.4 / −42.1: the Quartet lets more rumble through and blocks conversation harder than either.
⚠ vs. listeners — Whether it 'isolates well' depends on what you are trying to block. Office chatter and a train's upper harmonics disappear; engine and bass rumble come through more than on the cheaper Kiwi sets.
Sources split on time as much as taste. The majority — most 2023 reviews, the video class and the owner aggregates — call it an easy recommendation at $109 and the best bass all-rounder of its year. A substantial camp — the ranking critics, the IEMRanking aggregate, and 2024–26 owners cross-shopping the S08, EM6L, EG280 and Delci AE — says the tuning has been left behind and the money buys more clarity elsewhere; several suggest buying it used.
Where it splits
an easy recommendation — four usable tunings for $10975%
“What this set excels at is offering a pleasing energetic tonality at an affordable price, whilst giving new audiophiles the additional value of trying the tuning profile that works best for them.”
Meldrick, Headfonics
left behind — the same money buys more clarity now25%
“And if you’re willing to spend $200, you’ll find that the Kiwi Ears Quintet performs far better.”
Gabby Bloch, Major HiFi
