The FiiO FT15 is a full-size open-back planar magnetic headphone for home listening, built around a 101mm driver with an 800nm diamond-coated diaphragm. It is designed to give the resolution and low distortion of a large planar driver without the usual penalties: at 95dB/mW sensitivity and 24 Ohms impedance it runs happily from portable players and dongle DACs, and at around 425g it is lighter than most planar headphones of its size. It sits above the FT5 in FiiO's over-ear range, beneath the flagship FT7, and comes with a 4.4mm balanced cable, two sets of ear pads and a linen storage case. Available in one finish: black metalwork with North American black walnut ear cups.
800nm Diamond-Coated Diaphragm
The diaphragm is 800 nanometres thick, 86.7% thinner than the 6 micron film used in the FT5. FiiO applies a full-surface diamond coating by vapour deposition, which stiffens the film to reduce high-frequency break-up and extends the response to 40kHz, while a vacuum high-temperature treatment lowers the substrate's resonance point for deeper bass extension. The voice coil carries a silver-aluminium alloy coating for conductivity and is formed on the diaphragm by vacuum electroplating, a 28nm chip-grade process that bonds the conductor firmly to the film so it does not fatigue or detach over years of use.
101mm Planar Driver and Uniform Magnetic Field
The 101mm driver has an effective vibrating area of 6,443.5mm², 35% more than the FT5, which gives the FT15 its dynamic headroom, sub-bass reach and wide horizontal soundstage. FiiO's patented uniform magnetic field design uses custom-shaped high-strength magnets in a dual-sided heterogeneous array, tuned by finite element analysis so that the force on the coil stays even at every excursion level. That suppresses diaphragm break-up at source, lowers harmonic distortion, and keeps the coil in the strongest part of the field for the sensitivity that makes the FT15 easy to drive.
Build and Comfort
The centre frame of each ear cup is machined from FAS-grade North American black walnut and finished to show the natural grain, while the headband uses carbon fibre for low weight and rigidity. A modified-plastic magnet bracket with two-thirds the density of aluminium alloy and a lightened magnetic circuit bring the total weight down to around 425g, with a clamping force of 3.8N. Two sets of ear pads are supplied: suede pads (pre-installed) that deepen the bass and warm the vocals, and protein leather pads that lift high-frequency resolution and vocal clarity.
Cable and Accessories
The 1.5m cable is made from 6N monocrystalline (OCC) copper of up to 99.99998% purity, with each conductor given more than 100 hours of liquid-nitrogen cryogenic treatment at -192°C to relieve internal stress. It connects to the headphones through dual 3.5mm TS plugs and terminates in a 4.4mm balanced plug; a 4.4mm-to-6.35mm adapter and a 4.4mm-to-XLR-4 balanced adapter are included, so the FT15 can be used with single-ended and balanced amplifiers alike. A fabric Yaoli linen storage case completes the package. The FT15 is Hi-Res Audio certified by the Japan Audio Society.