FiiO FT15 Over Ear Headphones

The FiiO FT15 is an open-back planar magnetic headphone that, building on FiiO’s pioneering FT5, takes its own planar technology a generation further. Its 101mm driver has a diaphragm just 800 nanometres thick with FiiO’s first full-surface diamond coating, driven by a patented uniform magnetic field, for deep, solid bass, refined, easy-going mids and highs and an overall warm, natural sound. At 95dB/mW it is easy to drive, and a carbon-fibre headband and black walnut frames keep it to 425g. It comes with a cryogenically treated 6N copper cable, two sets of earpads, 6.35mm and XLR adapters and a linen storage case, and it is Hi-Res Audio certified.

800 nanometres: a generational leap in thinness

The FT15’s diaphragm is 800 nanometres thick, down from 6 microns in FiiO’s previous generation: 86.7% thinner, and approaching the physical limits of the material. Other planar headphones in its class use diaphragms of a micron or more. A thinner diaphragm improves the sound across the board:

• Resolution: faster transient response, so even subtle high and ultra-high frequency signals are reproduced with greater precision.
• Fidelity: the diaphragm follows the signal closely, starting and stopping with it and with minimal ringing, for a very clean, refined sound.
• Comfort: greater compliance and lower distortion give smooth, refined highs that stay comfortable over long sessions.

FiiO’s first diamond-coated diaphragm

FiiO’s patented multi-layer coating technology (patent ZL2024205488218) builds the diaphragm in layers: a PET substrate, a silver-aluminium alloy coating on the voice coil for better mechanical performance and conductivity, and a full-surface diamond coating on top. Diamond is hard and structurally stable, which is why it is often used for tweeter diaphragms in high-end loudspeakers. Applied by vapour deposition, it forms a stable reinforcing layer that reduces high-frequency break-up and speeds up the response, extending the frequency response to 40kHz, and because it resists fatigue under prolonged vibration, the sound stays consistent over the long term. A vacuum high-temperature treatment then tunes the substrate’s natural frequency, lowering its resonance for deep, powerful bass.

A 101mm driver for a grander sense of scale

The diaphragm’s effective vibrating area sets how much bass energy and scale a planar can deliver. The FT15’s full-size 101mm driver has an effective area of 6,443.5mm², 35% more than the FT5, which gives it real dynamic impact and sub-bass reach. With large works such as full symphonies, it presents a wider, more natural soundstage and handles rapid dynamic swings with ease.

A patented uniform magnetic field

Conventional rectangular magnets concentrate their energy in a narrow field and push the coil traces unevenly, which limits sensitivity and causes break-up and distortion. The FT15’s patented uniform magnetic field (patent ZL202420884963.1) combines custom-shaped, high-strength magnets with precisely optimised alignment, tuned by finite element analysis. The field is more even and covers a wider area, so more of the diaphragm is driven, raising sensitivity, and the force on every part of the coil stays even at all excursions, suppressing non-linear break-up and significantly reducing harmonic distortion.

A 28nm chip-grade process

Conductive traces on planar diaphragms have long been prone to fatigue and breakage. The FT15 borrows a precision process from semiconductor manufacturing: vacuum electroplating forms the voice coil evenly on the diaphragm and greatly strengthens its bond with the substrate, so it stays firmly attached through prolonged vibration for consistent, stable sound over time. Proven across several FiiO products, the process brings the chance of vibration damage to the coil close to zero.

Easy to drive, ready for portable hi-fi

A dual-sided heterogeneous magnet array, optimised by finite element analysis, keeps the voice coil in the strongest part of the field for ample driving force. With a sensitivity of 95dB/mW (111dB/Vrms) and an impedance of 24Ω, the FT15 can be driven easily by portable players and dongle DACs as well as desktop amplifiers, for a full, solid sound wherever you listen.

Light at 425g, with a carbon-fibre headband

Planar headphones are traditionally heavy, so FiiO’s engineers optimised the materials, structure and magnetic circuit to bring the FT15 down to 425g (without cable), more than 50g lighter than conventional planar headphones. The headband is carbon fibre, costly and difficult to work with but light, rigid and tough, and its optimised structure avoids excess weight and unwanted twisting or deformation. The clamping force is 3.8N (±0.3N).

North American black walnut

The centre frames of the earcups are FAS-grade North American black walnut, a wood used in luxury car interiors, fine furniture and premium musical instruments. FAS (Firsts and Seconds) is a top grade for North American hardwood, with more consistent grain, fewer natural imperfections and better workability than standard wood. Each pair is carefully finished and polished to preserve the natural grain, so no two are quite alike: as much a collectible as a pair of headphones.

A liquid-nitrogen-treated 6N copper cable

The cable uses 6N OCC monocrystalline copper with a purity of up to 99.99998%: with no grain boundaries, it has low resistance and high conductivity, and resists interference from oxygen and hydrogen impurities. Each conductor spends more than 100 hours in liquid-nitrogen cryogenic treatment at −192°C, which releases internal stresses and optimises the metal’s microstructure for a smoother, clearer, more distinct sound. FPA insulation subtly tunes the mid and low frequencies, adding just the right amount of colour, so the timbre is transparent yet open and relaxed. Four 21AWG conductors are coaxially twisted inside a TPU inner sheath and a nylon outer sheath; the cable is about 1.5m long, with a 4.4mm balanced plug and dual 3.5mm TS connectors at the headphones.

A 4.4mm-to-6.35mm adapter connects it to standard headphone sockets, and an XLR-4 (male) to 4.4mm (female) adapter connects it to balanced desktop amplifiers, so you can connect, upgrade and enjoy the FT15 in more ways.

Two sets of earpads to tune the sound

The FT15 comes with two pairs of earpads, so you can adjust its sound and comfort. The pre-fitted suede pads give a fuller bass, warmer vocals and smoother highs, ideal for pop and vocal music. The protein leather pads bring more treble clarity and vocal definition, particularly suiting classical music, instruments and female vocals. FiiO’s frequency response graph shows the difference.

A linen storage case

The FT15 comes with a custom Yaoli linen storage case, made with the same materials and craftsmanship found in high-end French luxury goods: durable, elegant and protective wherever you take your headphones. The FT15 is certified for high-quality audio by the Japan Audio Society (Hi-Res Audio).

Good to know

• Open-back: sound passes in and out, so the FT15 is best for listening at home.
• Walnut is a natural material, so the grain on your pair will differ from the photos.
• More FiiO planars: the FT5 that the FT15 builds on, the more affordable FT1 Pro, or FiiO’s flagship FT7.
• In the box: FT15 headphones, 4.4mm cable, XLR-4 to 4.4mm adapter, 4.4mm to 6.35mm adapter, suede (fitted) and protein leather earpads, linen storage case and quick start guide.