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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-19 · 7 min read · Independent comparison
• FiiO FT5 — biggest strength: a 90mm planar driver with a 6μm diaphragm and high sensitivity (110dB/1Vrms, 96dB/mW at 36Ω), so it plays loud off ordinary gear and sounds open and natural.
• FiiO FT5 — biggest trade-off: an open-back design leaks sound both ways. It is a listening-room headphone, not a silent one, and the 1.91 kg shipping weight hints at a full-size, at-home setup rather than a commute.
• Fostex T50RPmk4 — biggest strength: a 4th-gen RP planar driver built for response speed, which the spec sheet ties directly to localization and separation — exactly what competitive gaming needs.
• Fostex T50RPmk4 — biggest trade-off: it is a wired, 3.5mm-only headphone with no published impedance or sensitivity figures, so you get no easy answer about how hard it is to drive.
• Who each is for: the FT5 is for music listeners who want an open, musical planar without buying a dedicated amp; the T50RPmk4 is for gamers and studio-minded users who prize speed and channel matching.
The FT5 is FiiO's take on a full-size open planar, and the spec sheet reads like a comfort-and-drivability brief. The driver is a 90mm planar magnetic unit with a 6μm diaphragm — the sheet points out that is roughly a tenth of a human hair's thickness — paired with a micron-level aluminium-silver alloy coil and 20 neodymium magnets per driver for balanced force. In plain terms, that is a lot of motor and a very light moving part, which is the classic recipe for fast, low-distortion planar sound.
What makes the FT5 unusual is how easy it claims to be to power. At 36Ω with 110dB/1Vrms and 96dB/mW sensitivity, this is a planar you can plausibly run from a phone, a laptop jack or a small USB dongle. Most planars demand a proper amplifier; the FT5's numbers suggest you can skip that step and still get satisfying volume. Add a 7Hz–40kHz frequency range and an open-backed, magnesium-alloy frame, and you have a headphone built for long, relaxed listening at a desk.
The accessories are part of the pitch: a high-purity silver-plated monocrystalline copper cable with dual 3.5mm headphone-side plugs and swappable audio plugs, plus pre-installed 4.4mm and bundled 3.5mm, 6.35mm and XLR-4 adapters, protein leather and suede earpads, and a leather storage case. That is a lot of termination flexibility straight out of the box.
Fostex T50RPmk4: Who It's For
Fostex frames the T50RPmk4 as the fourth generation of its RP planar driver, a technology the sheet says has been refined over 50 years and used in professional studios worldwide. The headline claim is response speed — "overwhelming response speed," in Fostex's words — which it links to excellent localization and separation. For a gamer, that translates to hearing a footstep, a reload or a door creak as a distinct, placeable event rather than a blur inside the mix.
The second design point is genuinely interesting and not marketing fluff: Fostex says the left and right housings are symmetrical so that the presence or absence of connectors and internal parts does not create an audible difference between channels. In practice, matched channels mean a centred image and consistent panning — useful in games, and useful in any critical listening where you want left and right to behave identically.
Comfort gets real attention too. The new, thicker earpads are a low-resilience around-ear design, which the sheet says keeps the immersive experience intact over long gaming sessions. That is the right priority for a headphone you might wear for hours at a stretch. It is wired, with a 3.5mm jack, a synthetic-material black enclosure and a bundled cable.
Buy it if you game seriously and want a planar with studio lineage, matched channels and long-session comfort. Skip it if you need wireless, active noise cancelling or a spec sheet that tells you exactly how hard it is to drive — Fostex publishes the driver type and "wide range" frequency response but no impedance or sensitivity figures, so plan on treating it as an amp-friendly headphone until you know otherwise.
• Best for easy drivability → FiiO FT5. 36Ω with 110dB/1Vrms and 96dB/mW is a published, concrete case for running it off modest sources. The T50RPmk4 gives you no such numbers.
• Best for competitive gaming → Fostex T50RPmk4. Response speed, localization, separation and symmetrical left/right housings are the exact traits a positional-audio gamer wants.
• Best for open, natural music listening → FiiO FT5. An open-back 90mm planar with a 6μm diaphragm is designed for air and a wide, musical presentation.
• Best for long sessions → Fostex T50RPmk4. The thicker low-resilience around-ear pads are explicitly built for multi-hour wear.
• Best for cable and connection flexibility → FiiO FT5. Dual 3.5mm on the headphone end with swappable plugs, plus 3.5mm, 4.4mm, 6.35mm and XLR-4 options in the box.
• Best for a quiet shared space → neither, strictly speaking. The FT5 is open-back and leaks; the T50RPmk4's enclosure is closed-ish in materials but Fostex makes no isolation claim, and neither offers noise control.
• Best for studio-heritage appeal → Fostex T50RPmk4. A 50-year RP lineage used in professional studios is the whole story here.
• Best for desktop music-first buyers → FiiO FT5. A leather case, two pad sets and a full adapter kit signal a home-listening product, not a gaming peripheral.
If I had to pick one, I would buy the FiiO FT5. In my opinion, the published 36Ω, 110dB/1Vrms and 96dB/mW figures make it the safer purchase for most people, because it does not force you to budget for a dedicated amplifier to get decent volume. The 90mm driver, 6μm diaphragm and open-back magnesium frame point to the kind of spacious, musical sound I want for music and films, and the adapter kit means it fits whatever DAC or amp you already own. I would only steer you to the Fostex T50RPmk4 if gaming localization is your top priority — there, its response speed, symmetrical housings and thicker low-resilience pads are the more purpose-built answer.
By design intent, the Fostex T50RPmk4. Fostex built it around response speed, localization and separation, with symmetrical left and right housings for matched channels. The FT5 is a music-first open-back planar, and FiiO makes no gaming-specific claims for it.
Do I need an amplifier for the FiiO FT5?
Yes — it is a wired over-ear planar with a wide frequency range, so nothing stops you using it for music. Just note Fostex publishes no impedance or sensitivity figures, so you get less guidance on how it will behave with your particular source.
Fostex makes the stronger comfort case on paper, with thicker low-resilience around-ear pads described as comfortable over long gaming sessions. FiiO counters with a lightweight magnesium alloy frame and a choice of protein leather or suede earpads, so both are plausible all-day headphones — just for different reasons.
Whichever way you lean, check the current price on Amazon before you commit, since that is the one variable this comparison deliberately leaves out.
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