7 Total Dynamic, Balanced Armature, and Electrostatic Drivers

The FiiO FX25 is a hybrid IEM with one dynamic driver, two Knowles balanced armatures, and four Sonion electrostatic drivers in each earpiece. Acoustic chambers and a second-order RLC filter shape how the three driver groups work together, while carbon fiber shells keep each earpiece’s weight to approximately 0.25 ounces (7g). An included cable with interchangeable analog and USB-C DAC plugs accommodates listening from portable players, headphone amplifiers, and compatible USB-C devices.

Three driver technologies with dedicated roles

A 0.39-inch (10mm) dynamic driver handles bass using a lithium–magnesium alloy diaphragm and flexible polyurethane surround. The diaphragm combines low density with rigidity to limit moving mass and unwanted flexing, while the surround allows controlled diaphragm movement.

Two custom Knowles balanced armatures cover the midrange and its transition into the treble. One uses a vented rear chamber to increase airflow and diaphragm excursion in the lower midrange. Four Sonion EST65QB02 electrostatic drivers handle high and ultra-high frequencies. These electrostatic drivers are specified to extend to 50kHz, while the complete FX25 has a specified frequency response of 10Hz–40kHz.

Electrical filtering and acoustic tuning

The FX25 uses a second-order RLC band-stop filter to attenuate narrow resonant peaks associated with the drivers and acoustic chambers. This circuit shapes the treble response alongside the earphone’s acoustic tuning.

FiiO’s patented S.Turbo structure routes the dynamic driver’s output through a turbine-shaped sound tube. The path reinforces bass output while filtering unwanted midrange and treble energy from that driver, helping control its overlap with the balanced armatures. A small rear-chamber vent uses air damping to balance pressure across the dynamic driver’s front and rear chambers.

Carbon fiber shells

Multiple layers of carbon fiber form the FX25’s curved housings. The material combines low weight with rigidity and resistance to deformation, keeping each earpiece at approximately 7g excluding the cable. Variations in the carbon fiber weave give each pair a slightly different appearance.

One cable for analog and USB-C sources

The approximately 3.9-foot (1.2m) cable uses silver-plated 6N monocrystalline copper conductors and detachable 0.78mm 2-pin connections. FiiO treats the cable with liquid nitrogen at −313.6°F (−192°C) for more than 100 hours, a process the company describes as intended to release internal stress in the metal.

Interchangeable 3.5mm single-ended, 4.4mm balanced, and USB-C DAC plugs let you connect the included cable to different sources. A twist-lock mechanism secures each plug, while the detachable earpiece connections allow replacement with a compatible cable.

Fit options and included storage

The FX25 includes 22 pairs of ear tips spanning foam, silicone, double-flange, SpinFit, HS18, and HS20 liquid silicone options. These provide different shapes and materials for adjusting fit and achieving a consistent seal. The included NEST CUBE storage case combines aluminum alloy with PU leather.

Availability

The FiiO FX25 is available now on Apos.