Fiio FX15 review: Setting a new standard for flagship IEMs

Fiio is best-known for its value-focused products, but it has delved into the high-end segment over the last 18 months. The K9 Pro continues to be one of the best DACs you can buy today, and the R7 network streamer is an all-in-one device that offers an unmatched value. While Fiio has several dozen IEMs on offer, it was missing a halo product. Until now.

The FX15 uses a combination of three drivers — it has a dynamic driver, a balanced armature driver, and an electrostatic driver — and that distinguishes the IEMs from the rest of the offerings in the brand's portfolio. The design is also unique, and Fiio bundles a whole load of accessories with the package, but that isn't astonishing considering these are the brand's flagship IEMs. The FX15 are available for $749 on Amazon and major audio retailers around the world.

Let's start with the design, because there's a lot to talk about in this area. The FX15 feature a gorgeous design that includes a frond-like pattern around the faceplate, and this makes the IEMs look elegant. The shell is 3D printed and uses a photosensitive resin material, with Fiio noting that it once again collaborated with HeyGears over the manufacture of the shell.

What stands out about the FX15 is that the shell is actually see-through, the resin is translucent, and you get a good view of the drivers and the sound tubes. I'm a big fan of products with see-through designs — like the Nothing Ear (2) and Sharge Storm 2 — and Fiio deserves a lot of credit for the design of the FX15. Photos don't really do the product justice; you'll need to hold and use the IEMs to truly appreciate the elegance of the design.

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Going the 3D printing route gives Fiio tighter tolerances and better consistency, and at just 6g, they're incredibly light as well. Another unique trait is a toggle switch that lets you disable the electrostatic driver. Fiio says it added the switch so you can clearly make out the nuances that are delivered with the introduction of the electrostatic drivers, and that part is true — switching off the drivers leads to a flatter sound that isn't anywhere as engaging.

The build quality is among the best of any IEMs I've used, including the $2,299 Letshuoer Cadenza 12 I reviewed a few months ago. The design of the IEMs allows the sound nozzle to gently extrude outward, and they deliver a comfortable fit that doesn't exert much pressure even after several hours of use.

You get a lot of accessories with the FX15; Fiio bundles 19 ear tips in total, covering memory foam, silicone, and the brand's bass and treble-focused variants. You also get a cleaning brush, and a high-quality leather case. The case by itself costs $15 (the model name is HB5), and Fiio offers one of the best bundled cables in this category.

Fiio bundles a high-purity pure silver cable of 224 total wires that are divided into eight strands, and the Litz-style braid increases conduction. The best part about the cable is that it has interchangeable connectors, so you can easily switch between the single-ended 3.5mm and balanced 2.5mm and 4.4mm ports with the same cable without any hassle whatsoever. The cable connects to the IEMs via standard MMCX connectors.

Coming to the sound quality, Fiio's IEMs are known to deliver a neutral sound with a lot of technicality, and that's no different with the FX15. Each earbud uses a single 10mm dynamic driver, one Knowles balanced armature driver (ED-29689), and four Sonion electrostatic drivers. Fiio says it is went with four electrostatic drivers even though they cost a lot more than the others because it wanted to highlight their potential, even if it means losing out on sensitivity.

As such, the FX15 have a sensitivity of 103dB, and while that's still decent, you will need a good source to make the most out of these IEMs. I used the M15S player most of the time, but I also tested the monitors with the BTR7 and BTR5.

The FX15 have an excellent low-end, delivering bass with plenty of vigor and enthusiasm. The sub-bass has great texture and impact, and if you want a bit more exaggeration, the bass tips do a fantastic job in this area. The bass doesn't get overbearing, but it has a richer body than other Fiio IEMs I used.

Mids have good resolution and imaging, and vocals come through with a lot of clarity. The tonality is what sets the FX15 apart in this category, and the monitors are at their best when listening to ensemble orchestras with a lot of instruments. Treble is where the FX15 truly shine, as this is where the new drivers come into their own.

The EST drivers provide additional sparkle and airiness to the treble, and it is definitely noticeable. If you want a more balanced sound, you get the ability to toggle the EST drivers off, and in this scenario, the IEMs use the standard dynamic and the BA drivers. However, doing so means you lose a lot of the vibrancy.

Overall, the FX15 are the best-sounding Fiio IEMs by a heady margin. In fact, they're among the best you get in the sub-$1,000 segment, and that's a sizeable achievement. I like the design quite a bit, and even though the monitors don't use exotic materials like titanium, the 3D printed shells with the see-through aesthetic is a big differentiator.

You also get more accessories than you'll use in the box, and the fit is among the best in this segment. Yes, you're paying much more than traditional Fiio IEMs, but you're also getting a lot more for your money.