Introducing the FIIO FT15 with a 101mm planar driver and diamond-coated diaphragm

The FIIO FT15 is a full-size open-back planar magnetic headphone built around a 101mm driver with an 800nm ultra-thin diaphragm, a full-surface diamond coating, and a patented uniform magnetic field design. Developed from the FT5 planar platform, the FT15 increases the effective vibrating area while reducing diaphragm thickness by 86.7%. A redesigned dual-sided magnetic circuit provides the driving force needed to achieve 95dB/mW sensitivity at 24Ω, allowing the FT15 to operate with a wider range of sources, including portable players and dongle DACs. A 425g chassis, North American black walnut construction, and interchangeable tuning ear pads complete a design intended for both portable and desktop headphone systems.

An 800nm diaphragm with a full-surface diamond coating

The FT15 is is built around an ultra-thin diaphragm measuring just 800 nanometers, compared with the 6-micron diaphragm used in the previous-generation FT5. This 86.7% reduction in thickness lowers the moving mass of the diaphragm, allowing it to respond more readily to changes in the audio signal. The increased compliance also helps reduce unwanted vibration and distortion, particularly during rapid changes in signal amplitude.

FIIO reinforces the diaphragm using its patented multi-layer coating technology, which combines a silver-aluminum alloy voice-coil coating with a full-surface diamond coating. Diamond's high hardness and structural stability help the ultra-thin diaphragm resist deformation and control high-frequency breakup without substantially increasing its moving mass. A high-temperature vacuum treatment further lowers the substrate's resonance point to support low-frequency extension. Together, these engineering decisions contribute to the FT15's specified frequency response of 7Hz to 40kHz.

A larger 101mm planar magnetic driver

The FT15 uses a 101mm planar magnetic driver with an effective vibrating area of 6,443.5mm², approximately 35% larger than that of the FT5. The increased radiating surface provides greater displacement capacity for low-frequency reproduction and dynamic signal changes, while the thin diaphragm keeps moving mass low across the larger driver area.

Unlike a conventional dynamic driver, which applies force through a voice coil attached to a localized section of the diaphragm, a planar magnetic driver distributes conductive traces across a larger portion of its surface. The magnetic field acts on these traces to drive the diaphragm, helping distribute force across the vibrating area. The FT15 develops this architecture with a refined magnetic circuit intended to maintain consistent driving force and reduce unwanted diaphragm movement.

A patented magnetic circuit for more consistent driving force

FIIO's patented uniform magnetic field design uses custom-shaped high-strength magnets and optimized positioning to distribute magnetic flux more evenly across the diaphragm. By expanding the effective magnetic field, the circuit increases the usable voice-coil area and helps maintain consistent driving force as the diaphragm moves. This reduces uneven excitation that can contribute to nonlinear diaphragm behavior and harmonic distortion.

The FT15 also uses a dual-sided heterogeneous magnet array that keeps the voice coil within a strong portion of the magnetic field. The arrangement provides the magnetic force required to drive the larger diaphragm while supporting the headphone's relatively high sensitivity. FIIO has also optimized the magnetic circuit to reduce magnet weight without sacrificing the driving force required by the diaphragm.

28nm manufacturing for the voice coil

The FT15's voice coil is deposited directly onto the diaphragm using a 28nm chip-grade vacuum electroplating process. FIIO uses this manufacturing method to strengthen the bond between the conductive layer and the diaphragm substrate, helping the two materials remain securely joined during prolonged vibration.

A stable bond is particularly important in an ultra-thin planar diaphragm, where the conductive traces must remain attached while the diaphragm repeatedly flexes in response to the audio signal. The process is designed to improve consistency in diaphragm movement and reduce the likelihood of vibration-related damage to the voice coil.

High sensitivity for portable and desktop sources

With a nominal impedance of 24Ω and sensitivity ratings of 95dB/mW and 111dB/Vrms at 1kHz, the FT15 is designed to operate with a wider range of amplification than many traditional planar magnetic headphones. Its dual-sided magnetic circuit provides the driving force needed to achieve these sensitivity figures despite the relatively large 101mm diaphragm.

The 24Ω impedance and 95dB/mW sensitivity make the FT15 suitable for use with compatible portable digital audio players and dongle DACs, while conventional desktop headphone amplifiers remain an option. Available output voltage, current delivery, and the desired listening level will determine the power required from a particular source.

A 425g chassis with carbon fiber and North American walnut

The FT15 weighs approximately 15.0 ounces (425g) without its cable. FIIO achieves this weight through a combination of a carbon-fiber headband, a specialty modified-plastic magnet bracket, and the revised dual-sided magnetic circuit. The magnet bracket provides rigidity comparable to aluminum alloy at approximately two-thirds of its density, reducing structural weight while maintaining the support required to position the magnetic components.

The ear cup center frames are made from FAS-grade North American black walnut, selected for consistent grain and limited natural imperfections. Each piece is finished and polished to preserve the wood's natural pattern, giving individual headphones a distinct appearance. The open-back enclosure allows air to move through the rear of the driver rather than trapping it within a sealed ear cup. The FT15 has a specified clamping force of 3.8N ±0.3N.

Two ear pad materials for adjustable tuning

FIIO includes two sets of ear pads that allow listeners to adjust the FT15's tonal balance through a simple material change. The suede pads are tuned to emphasize bass warmth and produce a smoother treble presentation, making them suitable for listeners who prefer a warmer balance with pop music and vocal recordings.

The protein leather pads provide an alternative tuning that places greater emphasis on high-frequency definition and vocal clarity, with a presentation intended for classical instruments and higher-register vocals. Changing the ear pads modifies the acoustic interface between the driver and the listener's ear, allowing the tonal balance to be adjusted without electronic equalization or changes to the driver hardware.

A cryogenically treated 6N copper cable

The FT15 includes a 4.9-foot (1.5m) cable made from 6N OCC monocrystalline copper, with a stated conductor purity of up to 99.99998%. The conductors undergo more than 100 hours of cryogenic treatment at -313.6°F (-192°C), a process FIIO uses to relieve internal metal stress and refine the conductor's microscopic structure. FPA insulation surrounds the conductors.

The cable connects to the headphones through dual 3.5mm TS connectors and terminates in a 4.4mm fully-balanced plug. FIIO also supplies a 4.4mm-to-6.35mm adapter for conventional full-size headphone outputs and a 4.4mm-to-XLR-4 adapter for amplifiers equipped with four-pin balanced headphone connections. These options allow the same cable to be used with several common headphone output formats.

Included accessories and Hi-Res Audio certification

A custom Yaoli linen storage case is included to accommodate the FT15 and its accessories. The case provides a dedicated place to store the headphones, cable, adapters, and ear pads between listening sessions or during transport.

The FT15 also carries Hi-Res Audio certification from the Japan Audio Society. Its specified frequency response extends from 7Hz to 40kHz, covering the extended high-frequency bandwidth required for the certification.

Availability

The FIIO FT15 is available now on Apos.