FiiO FX25

Hybrid In Ear Headphones

• 1DD+2BA+4EST hybrid acoustic architecture
• Custom dual balanced armature drivers by Knowles (USA)
• Custom quad electrostatic drivers by Sonion (Denmark)
• Dynamic driver with lithium magnesium alloy diaphragm
• RLC second order band stop filter circuit
• Patented S.Turbo acoustic turbo structure
• Precision tuned resonant rear cavity
• Lightweight, high end carbon fiber shell
• Liquid nitrogen frozen, silver plated 6N single crystal copper cable
• Detachable cable with 0.78mm 2 pin connector
• Three interchangeable plugs included: 3.5mm, 4.4mm and Type C DAC
• Hi Res Audio gold label certified 

New Territory in Carbon, a Sound All Its Own

FiiO's next generation hybrid electrostatic IEM FX25

Built light through carbon, yet carrying the weight of music, the FX25 embodies a design philosophy of a light exterior over a solid core. Through its fine tuning it reaches a new sonic character, one that captures the dynamic pulse of contemporary pop production. With a fresh look and a fresh sound inside, the FX25 invites you to experience electrostatic sound in a new way.

Seven Drivers Per Side, One Precisely Divided Frequency Range

Each side of the FX25 combines one dynamic driver, two balanced armature drivers and four electrostatic drivers in a hybrid acoustic matrix. The dynamic driver handles the bass, the two Knowles balanced armature drivers take care of midrange precision and the transition into the highs, while the Sonion electrostatic drivers handle the high and ultra high frequencies. This seven way division of labor delivers a layered, balanced and fatigue free sound.

Custom Sonion Quad Electrostatic Drivers

Airy highs that seem to float beside the ear

The FX25 carries over the EST65QB02 electrostatic driver from Sonion, which already proved itself in FiiO's flagship FX17. Its frequency response extends comfortably up to 50kHz, delivering the overtone rich, airy sound that is characteristic of electrostatic drivers.

Custom Dual Knowles Balanced Armature Drivers

A refined core, fluidly blended

Two independent balanced armature drivers from Knowles are set up with a careful division of labor. One handles the upper midrange, improving clarity in the transition to the electrostatic drivers, while the other has an added acoustic vent in its rear chamber for greater airflow and increased diaphragm excursion, giving the low mids and midrange more body and warmth, which especially benefits vocals in pop music.

Dynamic Driver with Lithium Magnesium Alloy Diaphragm

Very low distortion, rich in detail

The 10mm dynamic driver has a diaphragm made from a lithium magnesium alloy with a density of only 1.6 g/cm³, lighter and stiffer than beryllium. Combined with a flexible PU surround, split vibration is noticeably reduced and response speed is improved, so that voices and instruments are reproduced accurately and realistically.

RLC Second Order Band Stop Filter Circuit

Precise control, pleasant and suited to long listening

The FX25 introduces FiiO's new RLC second order band stop filter circuit. Compared with the RC crossovers typically used in hybrid electrostatic IEMs, this circuit specifically removes the resonance peaks caused by the harmonic vibration of drivers and shell, so the transition in the treble range comes across as more natural and smoother. The overall sound stays balanced, is never harsh and is well suited to long listening sessions.

Patented S.Turbo Acoustic Structure

Filters out interference, boosts the bass

The front cavity carries over the patented S.Turbo acoustic structure, refined over several product generations. Inspired by the turbocharger of a sports car engine, the turbine shaped sound tube boosts bass energy and bass impact, making the bass deeper and more elastic, while at the same time filtering out excess upper midrange from the dynamic driver, so the transition to the low mids comes out smoother and fuller.

Patent number: ZL2018211416279

Precision Resonance Rear Cavity

Balanced internal pressure, clear, powerful sound

A precisely engineered rear cavity with a small vent uses air damping to balance the pressure in front of and behind the dynamic driver. This further improves bass extension while making vocals clearer and more transparent, since other frequency ranges mask the voice less.

Lightweight, High End Carbon Fiber Shell

Careful craftsmanship, subtle shimmer

High precision carbon fiber processing. The FX25 shell is made from carbon fiber, a material previously found mainly in flagship over ear headphones costing several thousand euros. Carbon fiber is complex to process, since the material has to be hand laminated in several layers before being shaped, and because of the high lateral stress as well as the small, strongly curved and irregular shape of an in ear shell, manufacturing is difficult, yield is low and production is correspondingly expensive.

Conventional resin shells tend to be comparatively low in rigidity, while metal shells tend to be heavier. Carbon fiber, with its low density of 1.58 g/cm³ and high rigidity, combines the requirements of low weight and high strength, so the shell is comfortable to wear while also being resistant to drops, pressure and deformation, making it very durable in everyday use. Compared with conventional shell materials, it is lighter and more durable, at a weight of only about 7g.

Since the grain of the carbon fiber forms randomly and naturally, the appearance of each earpiece varies slightly; the actual product is decisive.

Liquid Nitrogen Frozen, Silver Plated 6N Single Crystal Copper Cable

Treated at minus 192 degrees for pure sound

The conductor core is 6N single crystal copper with a purity of 99.99998 percent, silver plated for even better conductivity. Using the deep freezing process already established for premium cables, the cable is treated for more than 100 hours at minus 192 degrees in liquid nitrogen, which noticeably relieves internal stress in the metal and reduces signal transmission loss. Audibly, this results in a clearer, cleaner sound background with less graininess. Building on this, the development team further fine tuned the cable specifically for the sonic goals of the FX25, adding a fitting, light tonal coloration and balancing the low mids so the overall tonality comes across as warmer and more transparent.

Detachable Cable and Interchangeable Plugs

One headphone, many possibilities

The FX25 uses the widely adopted 0.78mm 2 pin connector, so the cable can be swapped for other cables with the same connector. Interchangeable 3.5mm, 4.4mm and Type C DAC plugs are included, allowing the FX25 to easily adapt to 3.5mm single ended or 4.4mm balanced sources, and it also remains free to upgrade to third party cables at any time.

Ear Tips and Official Carrying Case Included

Everything included, ready to listen right away

22 pairs of ear tips in three styles.

FIIO HS20: Food safe liquid silicone to the German LFGB standard, sits securely and gently on the skin, and enhances vocals and bass.

FIIO HS18: Bore matched to the sound tube for direct sound transmission, with a thin 0.4mm rim for a light, close fit.

SpinFit CP360: Medical grade silicone with a 360 degree rotating structure, for a high level of seal and a deep, secure fit, suited to sport and long wearing sessions.

Official carrying case: the FX25 comes with its own carrying case at no extra cost, in aluminum combined with PU leather for a refined, understated look.

Hi Res Audio Gold Label Certified

Lossless sound quality, faithfully reproduced

The FX25 holds the internationally recognized Hi Res Audio gold label certification, confirming that it precisely captures the original tonal character of music and reproduces it with balanced, Hi-Fi grade quality.

Specifications

Headphone type: Hybrid headphone with dynamic, balanced armature and electrostatic drivers

Wearing style: In ear, over ear cable routing

Drivers per side: 1x 10mm dynamic driver with lithium magnesium alloy diaphragm, 1x Knowles custom midrange balanced armature driver, 1x Knowles custom high frequency balanced armature driver, 4x Sonion electrostatic drivers

Frequency response: 10Hz to 40kHz

Impedance: 20Ω at 1kHz

Sensitivity: 106dB/mW at 1kHz

Cable: Liquid nitrogen frozen, silver plated single crystal copper cable

Cable length: approx. 1.2m

Weight per earpiece: approx. 7g (without cable)

Headphone connector: 0.78mm 2 pin

Audio plug: straight insert, twist lock, interchangeable

Color: Twilight Mountain Brown

Package Contents

Earphones x1 pair

FX25 packaging box x1

Quick start guide x1

NEST CUBE carrying case x1

Liquid nitrogen frozen, silver plated single crystal copper cable with interchangeable plug x1

Interchangeable 3.5mm/4.4mm plug x1

Type C DAC tuning plug x1

Assorted ear tips x22

Magnetic cable clip x1

Cleaning brush x1