FiiO FT15 Brings an 800nm Diamond-Coated Diaphragm to Planar Headphones

FiiO has introduced the FT15, a wired over-ear planar headphone featuring an ultra-thin diamond-coated diaphragm, large drivers and natural walnut earcups. The model follows the earlier FT5 while adding a revised planar driver system and an extensive selection of connection accessories.

An 800nm diamond-coated diaphragm

At the center of the FT15 is a diaphragm measuring just 800nm thick. FiiO says it is 86.7 percent thinner than the membrane used in the previous generation, reducing the moving mass to support a faster response to the incoming audio signal.

Making a diaphragm thinner can create challenges involving rigidity and controlled movement. FiiO addresses this by applying its patented diamond coating across the membrane’s entire surface. The company’s design combines low mass with increased stiffness, with the aim of helping the diaphragm move precisely rather than flexing unpredictably during playback.

The diaphragm sits within a pair of 101mm planar drivers. Each driver provides an effective radiating area of 6,443.5 square millimeters, giving the FT15 a substantial active surface for moving air. FiiO designed the large planar arrangement to convey scale and spatial information within recordings.

A redesigned magnetic system and voice coil

The FT15 also employs FiiO’s patented uniform magnetic-field design. Specially shaped high-strength magnets are positioned to control the force acting across the diaphragm, an approach intended to reduce diaphragm breakup and address distortion at its source.

A precision-electroplated voice coil completes the driver assembly. It is manufactured using 28nm chip-production technology and is designed to remain structurally stable while vibrating. According to FiiO, that stability also contributes to durability during extended use.

Together, the diaphragm, magnetic array and voice coil form an integrated planar system rather than functioning as isolated headline components. The design reflects FiiO’s focus on controlling the membrane consistently across its unusually large surface.

Designed for a broad range of headphone sources

Despite its large planar drivers, the FT15 is not intended exclusively for powerful desktop amplifiers. Its specified impedance is 24 ohms, while sensitivity is rated at 95dB per milliwatt. FiiO says these figures allow the headphones to work with sources ranging from compact USB DAC and amplifier dongles to portable audio players, dedicated hi-fi amplifiers and CD players.

That flexibility could make the FT15 suitable for both desktop systems and more compact personal-audio setups. FiiO specifically positions the headphones for use with products such as its QX13 dongle, K15 headphone amplifier and K17 R2R Pro, although the standard connection options also support equipment from other manufacturers.

Walnut earcups, carbon fiber and balanced cabling

The FT15’s earcups are made from North American FAS-grade black walnut. Because the wood retains its natural grain, the appearance will vary from one pair to another. A carbon-fiber headband helps keep the complete headphone weight to 425 grams.

FiiO supplies two sets of earpads, allowing owners to select between different sound characteristics. A fitted storage case is also included to protect the headphones when they are not in use.

The supplied cable uses 6N monocrystalline copper and undergoes cryogenic treatment as part of FiiO’s signal-transmission design. It terminates in a balanced 4.4mm connection, while included 6.35mm and four-pin XLR adapters expand compatibility with desktop headphone amplifiers and other audio components.

FiiO has announced the FT15, but confirmed regional availability details were not provided in the supplied information.

With its 800nm coated diaphragm, 101mm planar drivers and adaptable connection package, the FT15 expands FiiO’s over-ear range with a technically ambitious wired design. Its walnut construction and carbon-fiber headband add distinctive material choices to the underlying planar engineering.