Electrostatic IEMs are no longer a novelty in the high-end IEM landscape, but the FX15 is FiiO’s first foray into producing such a product. When developing the FX15, the FiiO R&D team spent much time researching how best to utilize electrostatic drivers. Due to the low sensitivity of such drivers, special care must be taken to ensure they are not overpowered by the other dynamic and BA drivers in use. Otherwise, listeners will not be fully able to experience the unique sound that electrostatic drivers bring to the table.
“Dare to be at the top” is an important part of FiiO’s corporate culture. FiiO does not merely use new techniques or materials simply to attract attention with new gimmicks, but rather chooses to fully research new methods to come up with products that fully utilize the potential of such new approaches. In a sense, “being slow makes you end up being faster.” The development of the FX15 embraces this ethos as the FiiO R&D team carefully made sure that dynamic, balanced armatures, and electrostatic drivers worked together in harmony to fully bring out the best of the latter before choosing to release this new IEM.
“Static” embracement of endless possibilities
Sonion electrostatic drivers
Electrostatic drivers are known for their high-frequency detail reproduction, but such drivers are usually used in extremely expensive IEMs out of reach out of most audiophiles. The FiiO FX15 employs 4 electrostatic drivers per channel that not only provide exceptional ultra-high frequency extension, but are exceptionally quick and able to reproduce every last detail in your music, giving the listener a taste of true high-end audio.
 Frequency response curve of the EST driver used in the FX15
Smoothly gentle A classic in the making Knowles mid and treble BAs
The FX15 adopts the proven Knowles ED-29689 balanced armature driver to handle the mids and lower treble frequency ranges, due to the driver’s smooth, lush, yet detailed sound. In addition, the R&D team reduced the sensitivity of this BA driver through the shell design and other methods. This ensures that the BA and electrostatic drivers output their respective frequency ranges without interference from each other – resulting in the two drivers working together in harmony with a smooth overall frequency response curve.
Rigid yet flexible Giving your music soul
10mm DLC dynamic driver
The FX15 features a 10mm DLC dynamic driver, chosen for its high rigidity, high damping coefficient, and other positive attributes – allowing the driver to deliver a robust, full sound that manages to be both highly detailed yet pleasant to listen to. And in order to achieve harmony between the dynamic, BA, and electrostatic drivers, the R&D team specially redesigned the structure of the dynamic driver, leading to a coherent sound from the bass to the ultra-high frequencies in the FX15’s frequency response curve.
Free of cerebral biases Instant AB Electrostatic on/off switch
We have added a switch that specifically turns on and off the electrostatic drivers, allowing the listener to instantly AB between having and not having the drivers. Easily and instantly experience the impact of electrostatic drivers on your music.
· On: Electrostatic driver is on
· — : Electrostatic driver is off
Electrostatic driver is off
Electrostatic driver is on
S.Turbo acoustic design
The FX15 tribrid IEM features the patent S.Turbo acoustic design designed to maximize bass performance. At the heart of the S.Turbo design is a lengthened low-frequency sound tube that effectively filters high-frequencies produced by the dynamic driver, so that the sound of the bass dynamic driver and mid-to-treble balanced armature driver are smoothly connected and do not interfere with each other for optimal sound quality.
 Patent no: ZL2018211416279
Exceptional sound Painstakingly crafted
Hi-end specially-tuned frequency response curve
Delicate sound Reminiscent of gingko beauty
“Sound and Form” harmonic design
The FX15 is a highly resolving IEM that is more than capable of reproducing sound frequencies above 15kHz. To visually represent its capabilities, the FX15 features a design that embodies the ethos of “sound and form” working together in harmony. The golden gingko leaves imposed on the FX15 shell cover serve as a visual reminder of its brilliant and vivid sound that fully allows the listener to discover the stories embedded within the music.
Industry Leader HeyGears
Custom 3D printed shell
FiiO cooperated with HeyGears to create a shell that features both excellent comfort and durability, to let the listener fully enjoy the highly resolving electrostatic IEM without worry. The FX15’s shell is made using the advanced DLP-3D printing method with printing accuracy down to 0.0375mm, ensuring that each FX15 shell is accurately molded to ensure highly consistent sound between every unit made. In addition, the FX15’s shell is made of photosensitive resin, which features high impact resistance, providing robust protection for the electrostatic and balanced armature drivers.
FiiO not only considers the shape and materials used for its IEMs, but also whether they are actually user-friendly. Through repeated measurements and wearing tests, FiiO engineers optimized the shape of the FX15, which is a triangle that not only feels comfortable to wear but also securely stays in the listener’s ear – for an ideal balance of comfort and stability.
Ergonomic triangular design
A good cable for great sound 224 wires 8 strands cable
The FX15 comes with a high-purity silver cable of 224 total wires separated into 8 strands of 28 wires each. Each wire is independently insulated and the cable features Litz braiding. The outer sheath is made of environmentally friendly TPU, not only allowing the cable to look more vivid and transparent, but also better protecting the cable against yellowing and hardening.
*The cable is identical to the LC-RD Pro 2022
cable features Litz braiding
Expanded MMCX connectors
Robust expanded MMCX connectors,
for greater connection stability
In-line twist-lock interchangeable audio plugs
3.5/4.4mm audio plugs with expanded
224 wires 8 strands cable
*The interchangeable audio plug is officially licensed from the patent by FABRILOUS
Headphone type: Dynamic BA Electrostatic Tribrid IEMs
Wearing method: In-ear, around-the-ear
Drivers: Knowles balanced armature*1
10mm DLC dynamic driver*1
Sonion electrostatic driver*4 (one driver unit contains 4 drivers)
Frequency response: 20Hz-40kHz
Cable: 8 strands totaling 224 wires of high-purity silver
Cable length: About 1.2m
Ear unit weight: About 6g (not including cable)
Earphone connector: Expanded MMCX
Audio plug: Twist-lock interchangeable plugs
“In the development of the FX15, we wanted to let the electrostatic drivers be the star of the show when reproducing sound. The sensitivity of a single balanced armature driver is 110dB. If we use multiple BA drivers, the frequency response range that the BA drivers cover will be even more prominent, overshadowing the other drivers. In other words, using too many BA drivers will not allow the listener to truly experience the brilliance of electrostatic drivers. Thus, we decided to employ one BA driver and four electrostatic drivers per ear.”