FIIO FX15

FiiO is a brand with great expertise in the field of in-ear monitors. Their extensive collection includes many models with various driver configurations and price tags. From the entry level 1DD FiiO JD3 to their previous flagship, the 1DD+6BA FiiO FH9. Yes, you have read that correctly, their previous flagship because the new one is the FiiO FX15. The first tribrid earphone by FiiO to include electrostatic drivers.

Technical

The FiiO FX15 is an 1DD, 1BA and 4 electrostatic drivers, tribrid earphone, the first such made by FiiO.

For the low frequencies, the FX15 features a 10mm DLC dynamic driver, chosen for its high rigidity, high damping coefficient. In order to achieve harmony between the dynamic, BA, and electrostatic drivers, the R&D team specially redesigned the structure of the dynamic driver. A vent at each earpiece helps to relieve the internal pressure and make for a fatigue-free listening experience.

The FX15 adopts the proven Knowles ED-29689 balanced armature driver to handle the mids and lower treble frequency ranges. The R&D team reduced the sensitivity of this BA driver through the shell design and other methods to ensure that the BA and electrostatic drivers output their respective frequency ranges without interference from each other.

The star of the show are the four electrostatic drivers by Sonion that mostly handle the high and ultra-high frequencies above 15kHz. FiiO has added a switch that specifically turns on and off the electrostatic drivers, allowing the user to instantly compare the sound with and without them.



Non Audio stuff

For the design and the construction of the FX15, FiiO has cooperated with the famous HeyGears to create an earshell that is made using the advanced DLP-3D printing method with printing accuracy down to 0.0375mm. The material used is photosensitive resin, which features high impact resistance, providing robust protection for the electrostatic and balanced armature drivers.

The custom-like shape of the FX15 is like a triangle that not only feels comfortable to wear but also securely stays in the listener's ear and offers very good isolation thanks to the mildly extended nozzle. The FX15 is also very lightweight thus offering a great wearing experience that makes it suitable for long listening sessions. The appearance is unique with a design pattern at the faceplate that is beautiful and discreet looking at the same time. The FX15 is one of the most comfortable, beautiful looking and well made earphone FiiO has made up to date.

Cable

The cable of the FiiO FX15 is worthy of a flagship. A well made and easy to handle detachable cable with expanded MMCX connectors for greater connection stability and longevity. It is a high-purity silver cable with 224 total wires separated into 8 strands of 28 wires each. Each wire is independently insulated and the cable features Litz braiding and an outer sheath that is made of environmentally friendly TPU. Furthermore, the cable has interchangeable, twist-lock, 3.5mm and 4.4m plugs. You can find less thick and more lightweight flagship cables but this is a really good one.

Accessories

FiiO is always generous when it comes to the included accessories. The contents of the FX15 package are illustrated in the following photo.



Power requirements and associated gear

The FiiO FX15 (24Ω/103dB) is relatively easy to drive but it scales incredibly well as it has a class leading transparency and mirror-like fidelity that demand the use of high quality sources. If you like a warm sound signature then use a warmer source and vice versa, the FiiO FX15 will always make sure to mirror the unique sound characteristics of every source. For this review I have mostly used the FiiO M15S, EarMen Angel and iBasso DX320.

Audio stuff

The FiiO FX15 has amazing clarity, mirror-like fidelity, class leading transparency and is one of the most refined and resolving earphones that you can buy without reaching the kilobuck categories. The FiiO FX15 combines excellent technicalities with a musical and engaging sound signature that is aided by a balanced tuning that pays equal attention to all parts of the frequency range.

Sub-bass extension is fantastic, the FiiO FX15 doesn't have any problem at faithfully reproducing the first octave without overpowering the rest of the frequencies. The low-end is weighty, punchy and dynamic with realistic contrast and excellent layering. The texture is not that visceral but not lean either, the bass is tight and very fast so it can easily follow the speed of the electrostatic drivers while it is crystal clear, controlled and well defined. The upper bass is slightly emphasized but not that much as to become tonally inaccurate or to mess with mid-range clarity and presence. The feeling is slightly warm, you can use the balanced or bass ear-tips for a mid-bass focused sound, that is suitable for more casual and fun listening moments, or switch to the vocal or SpinFit ear-tips when you need a more neutral bass tuning for critical listening. For an even more neutral bass you can use the FiiO HS18 ear-tips but they will also make the sound too dry, lean and bright.

The mid-range really shines thanks to its tonal accuracy, the harmonic richness and its timbre realism. The FX15 is musical and engaging, the voices are slightly prominent and the instruments play a supportive role without losing their presence and identity. The FX15 might be using only one BA for reproducing the mid frequencies but it is surprisingly articulate, resolving and refined. The texture is just a bit lean but not dry and by no means clinical. The mid-range has a realistic tonality for both instruments and voices without exhibiting any balanced armature timbre. Tonal balance is good, there is an upper mid-range emphasis but not as much as to cause listener fatigue unless you are listening to poorly recorded material.

The treble is delicate, ethereal and refined like a carefully woven spider web that might look fragile at first but it is strong enough to withstand the furious weather elements. Such is the treble of the FX15 which is finely shaped and sleek but still powerful and crisp with solid extension, exemplary transparency and top-notch definition. Sparkling, energetic and airy, shed with sun-bright light but not sharp or piercing, neither harsh or rough and really absent of any metallic timbre.

These are high frequencies at their best, the FiiO FX15 is made for listeners that seek crystalline clarity, class leading expensiveness and deep detail retrieval but at the same time don't sympathize with analytical, overly bright and clinical sounding earphones. I don't like bright earphones but the FiiO FX15 has instantly become one of my favorites despite its undeniably emphasized treble. This is because it is so refined and ethereal that it gets impossible to sound bright or piercing.

FiiO has done an excellent job into driver implementation and succeeded in making sure that the delicate and ethereal sound of the electrostatic drivers never gets overshadowed by the mid and lower frequencies. At the same time, the four electrostatic drivers never act like a spoiled prima Donna who tries to steal the show but they rather work in perfect harmony with the rest, producing an extremely cohesive and homogeneous sound.

The FX15 is open and wide sounding without any traces of congestion. There is plenty of air and space around the performers, positioning accuracy and imaging are exceptional, depth layering is excellent and there is plenty of ambient information that contributes to the overall sense of immersiveness and realism. What happens though is that the presentation is rather intimate, the listener feels as if sitting too close to the performers and the soundstage is mildly lacking in holographic expansion and the feeling of grandness.

The FiiO FX15 is very enjoyable with all kinds of music, especially if you take advantage of the various ear-tips for fine tuning the sound. But the truth is that this set is tailor-made for critical listening to classical and acoustic music. The better the recording and the quality of the source, the better your listening experience will be as this is an earphone that scales incredibly well.

The tuning switch

This feature is rather useless unless you are curious to find out how the FX15 can sound when you mutilate its electrostatic drivers. Switch off the electrostatic drivers to transform the FX15 from a flagship into an earphone that might sound a little smoother and less sharp in the treble but also lacking in treble quality, tonal balance and cohesiveness. One possible situation for using the switch is for listening to really bad and harsh sounding recordings or when you have a hissing source.



Cable upgrade

You can further enhance the sonic performance of the FiiO FX15 with a simple cable upgrade. Readers will already know that I am a great admirer of the Lavricables pure silver cables that I regularly use for reviewing and music listening. The Lavricables Ultimate is a well made and beautiful looking cable with high quality plugs, a soft feeling and great handling. These are not reasons of course to make you swap the already excellent stock cable.

But you can consider trying a Lavricables Ultimate because, subjectively speaking, it slightly enhances the transparency of the FX15, it helps it sound even more natural and refined, especially in the treble, the timbre becomes more realistic and the bass gains in control and definition. The better your source, the more noticable the differences are going to be but still we are talking about subtle sonic enhancements so don't expect something spectacular. Cable upgrades are always the cherry at the top of the cake when the rest of your audio chain is perfectly matched.



Compared to the FiiO FH9

The FH9 is FiiO's previous flagship, a semi-open, hybrid earphone with a very large 13.6mm DD and 6BA. Too many drivers that need a larger housing so the titanium-made FiiO FH9 is bulkier and heavier than the FX15. The fit is still quite comfortable, despite the size, but it really can't match the supreme comfort of the FX15 which is also much more effective at blocking external noise.

The FiiO FH9 has a bass dominant sound signature but it also manages to stay tonally balanced and well defined throughout the whole frequency range. Thus said, the bass on the FX15 is slightly faster and more controlled, a bit faster and more refined with better layering but while it is powerful and dynamic enough, there is no way to match the sheer power, the thundering dynamics and raw impactful force of the FH9.

I find the FH9 as slightly more resolving and refined in the mid-range, the sound is fuller and weightier while tonal balance and timbre realism are more or less the same between the two earphones. The opposite applies for the treble and the higher frequencies where the FX15 is the undeniable champion. Not only is way more resolving and refined but it is also considerably more natural sounding without any traces of metallic timbre. It extends better, it is crispier and more energetic with greater definition and finer articulation.

The FiiO FH9 offers a wider and more expansive soundstage, the presentation is grander and more holographic. There is more free space and air around the performers but the FX15 is doing much better with ambient information and positioning accuracy so while it might not be that grand sounding, it is more immersive and communicative.

Conclusion

The FX15 is the most resolving, refined and mature sounding earphone FiiO has made up to date. This is a critical listening machine that still manages to stay musical and enjoyable with all kinds of music. A living example that frequency measurements don't always tell the truth. A seemingly bright earphone that doesn't sound bright or piercing at all and maintains an excellent sound balance throughout the whole frequency range without causing listening fatigue. The FX15 is the most expensive earphone ever made by FiiO but it still retains the company's unprecedable price to performance ratio. This is not the end of the road but someone must spend considerably more money to get something better than the FiiO FX15 which offers flagship level performance without the flagship price tag.

The review sample was kindly provided free of charge.

The price of the FiiO FX15 is $749 and you can buy it from FiiO.eu

WELCOME TO THE PARTY
FiiO FX15

SETUP. 10mm DLC DD – 1BA (Knowles ED-296889) - 4 Sonion Electrostatic
SEN & IMP. 103dB/mW | 24Ω
PRICE. 799€ (sample for review by Zococity)

Click to expand...

RATING A
If I go straight to the point, it's not for me. I can think of several FiiO releases that I like more in profile than this FX15.

But if we value what is currently a "trending topic" tuning, the graphics of this FX15 should beloved for all SIMGOT fans (and other brands) that are launching headphones with: technical representations in the bass & lot of upper mids. FiiO wanted to get into that tuning, and it does so with a tri-brid that has no competition in what it offers... if the price were a little more contained. I can't recommend it, costing €100 more than the FH9, without being clearly superior to it, and personally liking more the top of the FiiO hybrids.

Let's not fool ourselves, it sounds like heaven, the packaging and construction are impressive, but it repeats accessories and conveys some laziness in the presentation of materials and design. But if FiiO wants to break the market as it has done in previous times, like they already done in DAPs and DACs, jumping on the train of "hyped" prices hurts me as a fan of the brand.

I insist again, if this headset does not have more impact, it is because there are brands that are positioning themselves better in forums and social media, but this is a launch to call all those people on the scene looking for timbre & perfect tones, for sure. The thing is that FiiO is not new to the business, and it cannot be forgiven for a launch that has lacked some effort in cost adjustment & final presentation; a shame, because sonically it has everything to succeed.

High-flying resolution, scene & timbre
The best exponent of the new "trending tuning"
Supreme quality capsule...
...which is clouded by a cheap earphone tubillon
You can notice laziness in the packaging
Bass can be "anemic" for bassheads
The price should be reconsidered
With the ON switch it´s somewhat burdensome in certain recordings

DISCLAIMER

I would like to thank Fiio for providing the FX15 review unit.
It can be gotten here (no affliate links): https://www.fiio.com/FX15





SPECIFICATIONS

• Driver configuration: 4 x Sonion Electrostatic drivers, 1 x Knowles ED-29689 BA, 1 x 10 mm DLC dome DD
• Impedance: 24 Ohms
• Frequency response: 20 Hz - 40 kHz
• Sensitivity: 103 dB/mW
• Cable: MMCX, high-purity 224-core sterling silver cable; interchangeable 3.5 mm and 4.4 mm modules
• Tested at $799.99 USD

ACCESSORIES

Other than the IEM, these are included:
- 3 x Spinfit silicone tips (S/M/L)
- 3 x HS18 silicone tips (S/M/L)
- 3 x "vocal" silicone tips (S/M/L)
- 3 x "bass" silicone tips (S/M/L)
- 3 x "balanced" silicone tips (S/M/L)
- 2 x dual flange silicone tips (M)
- 2 x foam tips (M)
- HB5 carrying case
- Cable
- 4.4 mm and 3.5 mm modular plugs
- Magnetic cable clasp
- Cleaning brush cum tuning switch pin
- MMCX release tool

The accessory line-up is truly fit for a king, and everything that an audiophile would require is included.




The vast array of eartips definitely ensures that all bases are covered! The tips even come in a nice little plastic case.

The dual flange tips provide the deepest insertion and isolation, though comfort may be an issue for those that are sensitive to longer tip depth. The Spinfit tips sound quite neutralish, with good comfort and fit, without coloring the sonics too much. The HS18 tips impart a warm neutral tonality, with decent fit and seal.

The other 3 silicone tips perform their functions as per their namesake:
- "Vocal" tips - boosts upper frequencies.
- "Bass" tips - boosts lower frequencies.
- "Balanced" tips - mid-point between the above 2 tips.

Last but not least, we have the foam tips, which tame treble, with an increase in isolation, though with some soundstage compression.

Do explore the various tips on offer, as eartips are as individual as shoes, in influencing comfort, seal, isolation and sound.




The stock cable is a high-purity silver cable with 224 wires braided in 8 strands, via a Litz configuration. It is also externally sheathed by TPU, which supposedly reduces yellowing and hardening over time. This cable is very well-braided and of good heft. There is minimal tangle, with a chin cinch for added grip. Unfortunately, some smattering of microphonics are noted during usage.

A selling point for this cable, is its modular plugs, with distal terminals that can accept 4.4 mm (balanced) and 3.5 mm (single-ended plugs), thus increasing the FX15's compatibility with various sources.




The MMCX removal tool is a nifty addition, to safely remove the MMCX cable, and we have a magnetic clasp to keep the cable tidily wrapped up. Fiio has creatively combined a cleaning brush with a card pin, which is used to flick the switches on this tunable IEM. Don't lose it!




Fiio's highly-sought after HB5 carrying case wraps up the goodie bag. This is one of the best carrying cases in the industry - the leatherette semi-rigid externals open to an inner velvety material, with a magnetic clasp. The insides can be compartmentalized through velcro webbing, and this case is definitely large enough to pack the IEM with additional room for other accessories.

The rest of this review was done with the stock cable and Spinfit tips. No aftermarket accessories were used, so as not to add any confounders to the sound.


BUILD/COMFORT

The FX15's housings are DLP 3D-printed from the renowned HeyGears company, utilizing photosensitive resin. The faceplates feature gold gingko leaves - this aesthetic choice was thought of by the tuners, as the flakes invoke thoughts of the FX15's brilliant and vivid sound signature.




The earpieces employ MMCX connectors - personally I'm not a fan of this connector type, especially with frequent cable changes - but the connectors here are quite premium; I had no issues connecting and disconnecting the cable, and they lock with a satisfying click. The MMCX allows slight rotation while the IEM is in the ears, thus assisting in fit and comfort in a way.

Weighing in at 6 g apiece, the shells are extremely light, yet build is very robust. Ergonomics are impeccable, with a concha protrusion added to assist in comfort. Indeed, I've been using the FX15 for the past few weeks without experiencing ear discomfort.




Isolation is good, despite the vented shells, and I did not encounter any driver flex.


DRIVABILITY

I tested the FX15 with the following sources:
- Apple dongle
- Cayin RU7
- Colorfly CDA M1 DAC/AMP dongle
- Creative Sound Blaster X5
- E1DA DAC/AMP dongle
- Hiby R3 Pro Saber 2022 DAP
- Khadas Tone Board -> Schiit Asgard 3 amp
- Khadas Tone Board -> Topping L30 amp
- Questyle M15 DAC/AMP dongle
- Sony Walkman NW A-55 DAP (Walkman One WM1Z Plus v2 Mod)
- Sony Walkman NW A-55 DAP (Walkman One Neutral Mod)
- Sony Walkman NW WM1A DAP (Walkman One WM1Z Plus v2 Mod)
- Smartphone

This IEM is very easily driven, and amplification is not 100% required. As the FX15 is a bright IEM, it finds kinship with sources that are bassier or warmer. Perhaps overly bright sources may not synergize well with this set.


INTERNALS/TUNING SWITCHES



This tribrid houses the following choice drivers:
- 1 x 10mm DLC dome DD handles the bass frequencies
- 1 x Knowles ED-29689 BA takes care of the midrange and lower treble
- 4 Sonion EST drivers settle the upper treble



Graph of the Fiio FX15 via IEC711 coupler. 8 kHz is a coupler artefact peak. The graph looks quite fierce, but it actually doesn't sound so shrill on actual listening!

The FX15 is the Fiio's first EST containing IEM. The FX15 comes with one tuning switch - in the "on" position (red graph above), the ESTs are brought into play and provide great treble sparkle and air. Turning off the switch deactivates the ESTs (blue graph above) and in this latter configuration, just the DD and Knowles BA are working.

On the red graph (ESTs activated), it is definitely the more resolving of the 2 tuning options, with lots of air and sparkle added to the equation. This transforms the FX15 into a technical behemoth - we will discuss this in more detail below - but suffice to say, on this setting, the FX15 handily beats most EST containing rivals at the MidFI segment when it comes to technicalities.

However, this EST-activated tuning is quite bright, and there are instances of sibilance. This tuning choice may hence be fatiguing for treble-sensitive folk. On the flip side, trebleheads and analytical-heads will love this setting to bits, and combined with the stellar technical prowess, good fit and isolation, this IEM can even be used for critical listening or audio work (eg mixing, stage monitoring etc).

For the treble-sensitive, we have the option of the blue graph, where the ESTs are turned off. On this setting, the FX15 becomes more balanced; it is slightly less resolving, with decreased sparkle and air, but a more controlled treble is found. On this blue graph, the FX15 still showcases solid technical prowess, but with decreased sibilance, and this would be a reasonable option for those that want something less intense or detailed-focused.

Of note, Fiio also makes use of a patented S.Turbo acoustic design in the FX15; basically, it is a thin and long acoustic tube, which is cleverly used to increase sub-bass quantity, as higher frequency sounds are dissipated first over a prolonged distance.


SOUND & TECHNICALITIES



The following impressions are done with the EST switch toggled on.

The FX15 has a mild V-shaped tonality with this setting.

As alluded to, the FX15 boasts impressive technicalities with the EST switch toggled on. When complex tracks with competing instrumental riffs are played, the FX15 handles these with aplomb, with no congestion or muddiness noted at all. Soundstage is expansive in all 3 dimensions, with pinpoint imaging and laudable instrument separation, allowing listeners to easily localize instruments on a dark background. Micro-detailing and resolution are stellar, and transients are lightning fast.

Unfortunately, there's a tinge of BA timbre heard in the higher frequencies, with woodwinds and piano notes sounding a tinge hollow, but by and large the timbre isn't as metallic as some other BA containing IEMs.

The FX15 is sub-bass focused. Sub-bass has decent extension and a slight rumble, though it is not a bona fide basshead set. The bass quality is splendid - texturing is well portrayed, and the bass is literally fast and clean, with no mid-bass bleed.

The lower midrange is very transparent and clear, with no big bleeding bass to eat into this frequency band. Instruments are given lots of space within the big soundstage, and clarity is very pronounced.

There's a 10 dB ear gain in the upper mids, and vocals are pushed forwards in the mix. This area lies at the border between shoutiness and forwardness. As per the Fletcher Munson curve, when the FX15 is used at low to moderate volumes, the upper mids just has mild instances of fatigue, but pushing the volume louder may overly boost this region.

The FX15 is a treblehead's wetdream. Furnishing lots of air and sparkle, the treble is very well extended with the ESTs activated. Resolution and clarity are the calling card of this IEM. There's some instances of sibilance, though high-hats and cymbals have bite without being too splashy.

Perception of treble and upper mids are influenced by ear anatomy (ear gain) and hearing health, not to mention the various sources and eartip synergy may also play a part, so this area is kind of a YMMV situation. I consider myself treble-sensitive, and thankfully the upper frequencies can be tamed with a few means - eartip rolling, moderate volumes (Fletcher Munson curve), and even utilizing a warmer source. In fact, I found the best synergy with warmish gear like the Cayin RU7 and Schiit Asgard 3; these sources thickened the bass/note weight and shaved off a little bit of the upper midrange energy, allowing me to use the FX15 on the EST setting for longer sessions.


COMPARISONS



Comparisons were made with other midFI EST-containing tribrids. Planars, single DDs and pure BA types were left out of the equation as the different transducers have their pros and cons.

Comparisons are made with the EST switch toggled on for the FX15.


Mangird Xenns Up

The Xenns Up is bassier, with less treble extension/air. The Xenns Up is a league behind in technical ability, with a more compressed soundstage, weaker imaging/instrument separation and lesser micro-details. The bass bleeds more on the Xenns Up too.

The Xenns Up has a thicker note weight and is more sedate in the upper mids/lower treble, though it has a more uncomfortable fit. The Xenns Up is not tunable unlike the FX15.



Moondrop Variations

The Variations is a Harman tuned IEM with a huge mid-bass scoop out, causing the lower midrange to sound anemic and thin. It has more sub-bass though, and is a bit less pronounced in the upper mids, with less air and sparkle than the FX15.

The Variations is noticeably worse in technicalities, with weaker imaging, soundstage and micro-detailing.

The Variations is a bit harder to drive. It is also not tunable, and may be less comfortable than the FX15.


Shuoer EJ07M

The EJ07M is smoother in the treble, but has a less tight bass, in addition to inferior technicalities. The EJ07M is claustrophobic in soundstage, and sounds very "in your head". Additionally, micro-detailing, imaging and instrument separation are not as good on the EJ07M.

The EJ07M is not tunable, and suffers from driver flex, which isn't the case with the FX15.


CONCLUSIONS

The FX15 is a very resolving beast, its forte is the excellent technicalities it brings to the table. Great air and sparkle is heard with the ESTs activated, and trebleheads will love this IEM. Soundstage is cavernous, with pinpoint imaging and appreciable micro-detailing and layering.

Additionally, the FX15's tuning switch confers versatility, allowing the FX15 to morph between an analytical treblehead infused sound (with the ESTs activated), versus a slightly less resolving IEM with a comparatively pulled back treble (with the ESTs turned off).

Other plus points are its easy drivability, and the accessories are second to none. Packaged with a modular cable, this IEM is easily paired with various single-ended and balanced sources. With the aforementioned top-notch technical prowess, and coupled with solid ergonomics, isolation and build, the FX15 will also perform well as a tool for audio work, eg in stage monitoring or critical listening.

The FX15 may be a bit spicy for treble-sensitive folk, what with the 10 dB ear gain in the upper mids and bright treble tuning. Thankfully, this area can be tamed with toggling off the EST drivers, or even with eartips or pairing the IEM with a warmer/bassier source. Bassheads may also need to look elsewhere, though the FX15 cedes bass quantity for excellent quality.

The FX15 is not the cheapest tribrid, but as per diminishing returns in this hobby, eking out that last few percent of technical performance may cost exponentially more. The FX15 will not disappoint when it comes to technical chops, it is easily one of the best midFI EST gear in this department.