FiiO FX25 Launches With 7 Drivers and Carbon Fiber Shells

The FiiO FX25 was launched today (October 19) in mainland China. Featuring a carbon fiber housing, the FX25 is an in-ear monitor (IEM) that combines durability with low weight. Its hybrid driver configuration comprises one dynamic driver (DD), two balanced armature drivers (BAs), and four electrostatic drivers (ESTs) per side. Its cable uses 2-pin connectors and includes three interchangeable plugs: 3.5 mm, 4.4 mm, and USB-C.

Update (November 1): The FiiO FX25 is now available from FiiO’s official store on AliExpress.

FX25 features seven drivers per side and a carbon fiber housing

With its hybrid driver configuration, the FX25 uses seven drivers per side to distribute sound reproduction across the entire frequency range. One DD handles the bass, two BAs cover the midrange and the transition into the treble, and four ESTs reproduce the treble and upper treble.

The carbon fiber housing gives the FiiO FX25 an attractive appearance, low weight, and resistance to damage from drops. An image of the IEM is shown below.

Four Sonion electrostatic drivers

Each side of the FX25 contains four electrostatic drivers developed by Danish manufacturer Sonion. The EST driver model used is the Sonion EST65QB02, implemented for high-frequency reproduction. According to FiiO, this choice produces an airy presentation with the sonic characteristics associated with electrostatic driver technology.

Two Knowles balanced armature drivers

To improve midrange performance while ensuring smooth transitions into the high and low frequencies, the FX25 uses two BAs with different roles.

One BA reproduces the midrange and lower treble. The other features an acoustic vent that allows air to enter and increases diaphragm excursion. This greater freedom of diaphragm movement gives the midrange and bass a fuller sound.

Lithium–magnesium alloy diaphragm

To reproduce bass with precision and texture, FiiO equipped the FX25 with a dynamic driver featuring a lithium–magnesium alloy diaphragm. The use of these metals provides lower weight and greater rigidity than beryllium.

Housing vent for balancing internal pressure

Driver operation increases internal pressure, which can impair the IEM’s sound reproduction. To address this issue, FiiO incorporated a small opening into the FX25 housing. According to the manufacturer, the small grille with multiple holes helps “balance the pressure between the front and rear chambers of the dynamic driver.”

FiiO describes the effect of this improved airflow as follows:

“Improves bass extension and makes vocals in the midrange clearer and more transparent, reducing masking by other frequency ranges.”

Crossover featuring FiiO’s proprietary technology

FiiO implemented a new crossover technology in the FX25: a second-order RLC band-stop filter circuit. According to the manufacturer, this solution “precisely filters out resonance peaks caused by harmonic resonances in the drivers and acoustic chambers.”

FiiO describes the effect of implementing this frequency-filtering system in the FX25 as follows:

“Provides more natural, smoother transitions in the treble response curve, resulting in a balanced sound without harshness, suitable for extended, immersive listening sessions.”

Modular cable with 2-pin connectors

The FiiO FX25 uses a cable with 2-pin connectors and allows users to replace the plug, providing greater flexibility in how the IEM can be used. Users can switch between 3.5 mm, 4.4 mm, and USB-C plugs.

The USB-C plug contains an integrated DAC/amplifier with the following specifications:

• Native decoding: PCM up to 32-bit/384 kHz
• Output power: 30 mW into 32 Ω
• Channel separation: −110 dB
• Noise floor: < 0.8 µV
• Distortion: < 0.001%
• Signal-to-noise ratio: > 122 dB

When using the FX25 cable with the USB-C plug, users can apply different equalization profiles through the FiiO Control app. The app also provides an eight-band parametric equalizer (PEQ), allowing greater flexibility in frequency adjustments.

Twenty-two pairs of ear tips included with the FX25

To provide comfort and a sound signature suited to individual preferences, FiiO includes 22 pairs of ear tips with the FX25. These include two models developed by the brand itself, the HS20 and HS18, as well as ear tips from SpinFit.

Users can choose between foam and silicone ear tips. The silicone options include a double-flange design, which provides greater isolation than the standard shape.

FiiO FX25: Specifications

• Cable conductor material: Silver-plated 6N monocrystalline copper
• Cable length: 1.2 m
• Cable plug: Interchangeable 3.5 mm, 4.4 mm, and USB-C plugs
• Color: “Mountains at Dusk” Brown
• Drivers per side: One dynamic driver (DD) with a 10 mm lithium–magnesium alloy diaphragm, two Knowles balanced armature drivers (BAs), and four Sonion electrostatic drivers (ESTs)
• Earphone type: In-ear monitor (IEM)
• Earpiece connector: 0.78 mm 2-pin
• Frequency response: 10 Hz–40 kHz
• Impedance: 20 Ω at 1 kHz
• Sensitivity: 106 dB/mW at 1 kHz
• Weight per earpiece: 7 g

What is included in the FiiO FX25 box?

The following items are included with the FiiO FX25:

1. One earphone cable made of cryogenically treated, silver-plated monocrystalline copper, with an interchangeable plug.
2. Interchangeable 3.5 mm and 4.4 mm plugs, with the 4.4 mm plug factory-installed.
3. One USB-C plug with an integrated DAC and sound-tuning functionality.
4. One pair of earphones.
5. One NEST CUBE carrying case.
6. Ear tip set:- Foam: Two pairs, size M.

• Bass: Three pairs, sizes S/M/L.
• Balanced sound: Three pairs, sizes S/M/L, with size M factory-installed.
• Vocals: Three pairs, sizes S/M/L.
• Double-flange: Two pairs, size M.

7. HS20 liquid silicone ear tips: Three pairs, sizes S/M/L.
8. SpinFit ear tips: Three pairs, sizes S/M/L.
9. HS18 ear tips: Three pairs, sizes S/M/L.
10. One magnetic cable organizer.
11. One small brush for cleaning the connector pins.
12. One FX25 packaging box.
13. One quick start guide.

Launch, pricing, and availability

The FiiO FX25 is now available internationally for $781.04 from FiiO’s official store on AliExpress.