By aspect — in detail
The calling card: a huge, deeply extended sub-bass with real slam and rumble that most call clean rather than muddy. Benches read it as boosted-but-not-extreme (~6 dB lift) with strong sub-bass reach, its presence intensified by the scooped low-mids. Two dissents keep it from a clean sweep — a few hear it as slightly boomy on some tracks, and a minority who expected a TH-X00-style bass cannon find it 'thin.'
“The low end is absolutely immense, going right down to 5hz”
Reddit — r/headphones (Sir_James811)
“a stronger low-end texture and a much deeper visceral kick. It can perhaps almost verge on the slightly boomy with some recordings”
Headphones.com
“Fact is they are quite thin sounding and the bass isn't really that boosted.”
Reddit — r/headphones
Measured
Sonarworks measures a 'relatively conservative' ~6 dB bass boost with the low-end presence intensified by the reduced low-mid region, and deep sub-bass extension; unheardlab hears more extension and slam than the E-MU Teak. The 'thin bass' reading comes from listeners expecting a TH-X00-style bass cannon — this is a boosted, sub-focused low end, not a bloated one.
Recessed and laid-back, exactly as a V-shape implies — but broadly agreed to be detailed and clean rather than hollow, so vocals sit a step back without disappearing. The caveat is a jumpy upper-mid/lower-treble region that can push certain vocals forward and turn 'spikey' or harsh on some tracks.
“The middle frequencies feel a bit scooped in the Fostex TH900mk2.”
Major HiFi (Steph Durwin)
“The mid-range is nothing amazing as what you would expect for a V-shaped headphone but it has plenty of detail and is quite laid back.”
Reddit — r/headphones (Sir_James811)
Measured
The V-shape scoops the midrange and low-mids; Sonarworks notes the high-mid dip that helps make the tuning read bright. Reviewers put vocals a step back, though a peak in the upper-mid/presence region can jump forward on some material — Major HiFi's 'spikey' vocals, and one owner's near-'unbearably harsh' moment on a whistle-register track.
The headline disagreement, and the same objectively very bright top end drives both readings. Everyone agrees the graph is hot (roughly 6–9 dB of lift with peaks near 6 and 11 kHz). The split is whether that lands as exciting, extended sparkle or as a fatiguing, even piercing glare that's a dealbreaker — a split that tracks hard with the source, amp, EQ, pads and the listener's treble sensitivity. Many owners pair a warm (often tube) amp or EQ a peak down to live with it.
Measured
The FR really is very bright: unheardlab measures 'Two huge spikes in the sibbilance region (9db boost at 5.8khz and 11khz)' that make it brighter than the HD800, and Sonarworks measures 'about 9 dB from 6 kHz onwards.' It's objectively elevated.
⚠ vs. listeners — The treble lift is real and large, so this isn't a case of the graph disagreeing with ears — it's that 6–9 dB of peaky treble lands very differently depending on the source/amp (a warm tube tames it), EQ, pads, recording and how treble-sensitive you are, which is exactly why owners split and so many reach for EQ or a warm chain.
Where it splits
Too bright — hot, fatiguing, even piercing/sibilant, and a real dealbreaker for many.66%
“Vocals can sound artificially bright or even piercing on some tracks.”
unheardlab
Bright but exciting and manageable — only a hint of extra energy, tamable with a warm chain or EQ.34%
“we did detect a tiny hint of upper frequency tizziness - most notably in the hi-hat & cymbals”
Headphones.com
Broad agreement on the character, not on whether you'll want it: a distinctly V-shaped, not-neutral tuning with elevated bass, scooped mids and a lifted treble. Whether that overall balance reads as 'warm and fun' or 'bright and cold' depends on the listener and the chain — the same shape, framed two ways.
“VERY V-shaped kind of sound. Mids are a lot more withdrawn than the Teak.”
unheardlab
“I find these headphones to have a very V-shaped sound signature, almost to a fault.”
Reddit — r/headphones (Sir_James811)
“Tuning is towards the warm side with powerful bass and treble presence complimented by smooth mids.”
Audiophile On
Measured
Both benches confirm the shape — elevated bass (~6 dB), a scooped high-mid, and a strong treble lift (~9 dB from 6 kHz): a textbook V. Sonarworks calls the overall impression 'bright-sounding'; the debate is taste, not the graph.
Soundstage
Moderate · 6 srcA consistent strength for a sealed design — reviewers repeatedly call it wide and open for a closed-back, helped by the fact that it leaks like a semi-open headphone. The caveat is comparative: against open flagships (and a couple of pricier closed rivals) the stage narrows.
“They had a remarkably impressive sense of spatial depth and width, especially for a pair of closed-back cans.”
Major HiFi (Steph Durwin)
“the TH900mk2's have a surprisingly wide soundstage for a pair of closed-back headphones.”
Reddit — r/headphones (Sir_James811)
“the Audeze XC and the Ether C to be wider and deeper than the narrower perspective of the Fostex”
Headphones.com
Measured
It isn't a truly sealed design — it leaks considerably (Sonarworks, Headphones.com), which likely helps it sound more open than most closed-backs; unheardlab measured its pads as roomier and the stage as much wider than the E-MU Teak's.
Widely praised: pinpoint placement with excellent layering and separation that several rank near far pricier open flagships. The one recurring nit is that dead-center vocals can smear a little.
“I can accurately pinpoint the exact location every instrument going on around my head”
Reddit — r/headphones (Sir_James811)
“Layering and separation are top-tier, about on par with the HD800/T1/Utopia.”
unheardlab
Detail
Strong consensus · 5 srcA genuine standout and, after the bass, the most-praised trait: fast transients and high resolution that reviewers repeatedly rank among the best, with more than one comparing its speed and detail to electrostatics. The elevated treble accentuates the sense of clarity.
“What TH 900 does spectacularly well is its technical capabilities i.e speed/transient response and detail retrieval. I find it rivals my Stax headphones in this regard.”
Reddit — r/headphones
“these headphones are oozing with detail”
Reddit — r/headphones (Sir_James811)
Measured
The Foster biodyna driver measures near-negligible distortion (Sonarworks rates THD 9/10), and its speed plus the lifted treble push perceived resolution high — which is why the same set that some find fatiguing is also called one of the most detailed closed-backs going.
Dynamics
Strong consensus · 4 srcAnother clear strength: effortless slam and quick, punchy transients that reviewers single out as among the best around, contributing to the headphone's lively, foot-tapping character.
“Macrodynamic qualities are magnificent, arguably one of the best out there period.”
unheardlab
“Their quick transient response and dynamic range really set instruments apart from each other top-to-bottom”
Major HiFi (Steph Durwin)
Measured
The big, sensitive Foster driver plays loud and clean; Headphones.com credits it with the 'quick dynamics' once reserved for open flagships, and owners describe slam and speed that rival electrostats.
Mostly comfortable, and lighter than it looks (~390 g) with well-distributed weight and low clamp — good for long sessions to most. The asterisks: the relaxed clamp means a loose seal that slides with head movement, the closed cups build heat over time, and the headband design is dated.
“I was shocked at how light they were given the size and materials used.”
Audiophile On
“The weight (which is quite low to begin with) is efficiently distributed across the head, making them feel even lighter”
Sonarworks
“you still suffer from heat build-up over time.”
Audiophile On
Measured
Weight is ~390 g without cable (Sonarworks). Clamp is light, which aids comfort but loosens the seal — Sonarworks warns sudden head movements make them slide around, and smaller heads may lose a little bass from the imperfect seal.
Build
Strong consensus · 6 srcA near-universal high point: Japanese cherry-birch cups in traditional Urushi lacquer on a mostly-metal frame, widely called gorgeous and genuinely premium, and better built than some pricier rivals. The mk2 adds a detachable 2-pin cable over the mk1; the knocks are a thick, stiff supplied cable and pads that can flake with age.
“The TH-900 feels better built and sturdier than the Stellia, with more metal and wood and less plastic.”
Headphoneer (Chris)
“Build wise the 900's are far and beyond above average.”
Reddit — r/headphones (Sir_James811)
Measured
50 mm Foster 'biodyna' driver with a 1.5-tesla magnet; Japanese cherry-birch cups in traditional Urushi lacquer, a mostly-metal frame and protein-leather pads; ~390 g. The mk2's defining change over the 2012 mk1 is a detachable 2-pin cable — Fostex confirmed to reviewers the two are otherwise identical.
Isolation
Moderate · 3 srcA weak point, and a design trait: it's effectively semi-closed, so it leaks and blocks outside noise more like a partly-open headphone than a sealed one. Buy it for the sound, not to isolate on a commute.
“The sound is very open but passive noise cancellation is weak and sound leakage considerable.”
Sonarworks
“you might consider it semi-closed as it does seem to isolate a bit less than truly closed headphones.”
Headphones.com
Measured
Both a bench reviewer and editorial reviewers flag weak isolation and considerable leakage; owners report it bleeds sound much like an open-back, which is part of why the stage sounds open.
The other real split. At ~$1,500 (MSRP $1,599) it's a true flagship price. One camp calls it hard to justify — cheaper closed-backs, and its own far-cheaper TH-X00 sibling, get you much of the way. The other argues it earns it: a unique sound, standout technicalities and superb build, undercutting closed rivals like the Focal Stellia and Sennheiser HD 820.
Measured
MSRP $1,599 (Sonarworks), typically around $1,500 street. Its cheaper Fostex TH-X00 sibling uses a closely related Foster driver for a fraction of the price, which anchors the skeptical camp, while fans note it still undercuts closed flagships like the Focal Stellia and Sennheiser HD 820.
Where it splits
Hard to justify — cheaper closed-backs (and its own TH-X00 sibling) deliver much of it for far less.58%
“the gains over other great closed cans that cost less than a third of what Fostex is asking, are negligible if any.”
Sonarworks
Worth it — a unique, superbly built flagship that undercuts rivals like the Stellia.42%
“costs much less than the Stellia, is better built and more comfortable.”
Headphoneer (Chris)
