FiiO FX15 Six-Driver Hybrid In Ear Monitors

The FiiO FX15 is a tribrid in-ear monitor and FiiO’s first with electrostatic drivers. Each earpiece combines four Sonion electrostatic tweeters for the highest frequencies, a Knowles balanced armature for the mids and treble, and a 10mm DLC dynamic driver with FiiO’s patented S.Turbo bass tube, and a switch on each earpiece turns the electrostatics on or off so you can hear exactly what they add. The shells are precision 3D-printed by HeyGears, and a 224-wire silver cable with twist-lock 3.5mm and 4.4mm plugs is included. It is Hi-Res Audio certified and won a CIHE EHA 2023 Silver Award and a VGP 2024 Summer award.

Slow is fast

Electrostatic IEMs are no longer a novelty at the high end, but the FX15 is FiiO’s first. Electrostatic drivers are not very sensitive, so they are easily drowned out by the dynamic and balanced armature drivers around them, and FiiO’s team spent a long time on getting them to work in harmony before releasing it. As FiiO puts it, being slow makes you end up faster.

Four Sonion electrostatic drivers

Electrostatic drivers are known for high-frequency detail but are usually found only in very expensive IEMs. The FX15 has four per side, giving exceptional ultra-high-frequency extension and the speed to reproduce every last detail: a real taste of high-end audio. It comfortably reproduces sound above 15kHz.

A Knowles balanced armature for mids and treble

The proven Knowles ED-29689 handles the mids and lower treble with its smooth, lush yet detailed sound. FiiO reduced its sensitivity through the shell design and other measures, so the balanced armature and the electrostatics each cover their own range without getting in each other’s way, for a smooth overall response.

A 10mm DLC dynamic driver

The 10mm DLC (diamond-like carbon) driver was chosen for its high rigidity and damping, for a robust, full sound that is detailed yet easy to listen to. FiiO redesigned its structure so the three driver types join up coherently from the bass to the very top.

S.Turbo bass

FiiO’s patented S.Turbo design (patent ZL2018211416279) uses a lengthened low-frequency sound tube that filters the higher frequencies out of the dynamic driver’s output, so the bass driver and the balanced armature join smoothly without interfering, for the best bass performance.

Electrostatics on or off

A switch on each earpiece turns the electrostatic drivers on (“On”) or off (“—”), so you can compare instantly and hear their effect on your music for yourself.

“Sound and form”

The faceplates carry golden ginkgo leaves, a visual reminder of the FX15’s brilliant, vivid sound and its ability to reproduce frequencies above 15kHz, in a design built on the idea of sound and form in harmony.

Shells 3D-printed by HeyGears

FiiO worked with industry leader HeyGears on shells that are comfortable and durable. They are DLP 3D-printed to an accuracy of 0.0375mm, so every FX15 sounds consistent, in a photosensitive resin with high impact resistance to protect the electrostatic and balanced armature drivers. After repeated measurements and wearing tests, FiiO settled on a triangular shape that is comfortable and stays securely in your ear.

224-wire silver cable

The included cable is high-purity silver: 8 strands of 28 wires (224 in all), each individually insulated and Litz-braided, in a clear, environmentally friendly TPU sheath that resists yellowing and hardening. It is the same cable as FiiO’s LC-RD Pro 2022, with robust expanded MMCX connectors and in-line twist-lock 3.5mm and 4.4mm plugs (4.4mm fitted; a design licensed from FABRILOUS).

Good to know

• FiiO ships either the new or the older design of interchangeable plug; both are genuine and the cable is the same.
• Plenty of tips for the right fit: three pairs each of balanced (M fitted), vocal, bass, SpinFit and HS18 tips, plus two pairs each of dual-flange and foam tips.
• In the box: FX15, silver cable with 3.5mm and 4.4mm plugs, HB5 carry case, ear tips, magnetic clip, cleaning brush, MMCX quick-release tool and manual.
• FiiO’s flagship with eight electrostatic drivers is the FiiO FX17.