In this article, I review the new FiiO FD15 IEM. The FD15 features a 13.8mm Magnalium Diamond-Like Carbon (DLC) dynamic driver and stainless steel shells. It’s priced at $149.
Disclaimer: This sample was provided by FiiO for an honest review. All observations and opinions here are my own, based on my experience with the product.
FiiO FD15
Table of Contents
Specifications
Driver: aluminium-magnesium dynamic driver
Frequency response: 10Hz-40kHz
Impedance: 32Ω@1kHz
Sensitivity: 112dB/mW@1kHz
Single unit weight: about 12g (excluding cable)

In the Box
- FiiO FD15 IEMs
- Detachable MMCX silver-plated copper cable
- Balanced eartips *3 pairs
- Vocal eartips *3 pairs
- Bass eartips *3 pairs
- Foam eartips *2 pairs
- HS18 eartips *3 pairs
- Storage case
- MMCX quick-release tool
- Cleaning brush
- 3.5mm/4.4mm swappable plugs
- Red/Black swappable sound nozzles *2 pairs
- Quick start guide

Design
The FD15’s shells feature a short cylindrical design, crafted from 316L stainless steel. They undergo a meticulous hand-polishing and PVD electroplating process, resulting in a flashy yet durable finish. Despite the polished surface, the IEMs are surprisingly resistant to fingerprints. They also appear to withstand micro scratches well, though only time will tell the full extent of their durability.
FiiO has chosen to maintain the MMCX connectors rather than 2-pin – whether that is a pro or con will depend on personal preference. There’s one vent at the base of the MMCX socket housing and another at the base of the nozzle. These nozzles also act as sound filters and you can easily swap between the black and red filters to change the sound profile.

FiiO clearly prioritized comfort in the FD15’s design, and they’ve succeeded admirably. The IEMs fit my ears exceptionally well, allowing for extended listening sessions without discomfort.

FD15’s cable is made from a blend of monocrystalline silver and silver-plated copper. It’s a little bulky but feels durable and it handles well. In addition, it’s a modular cable and comes with 3.5mm and 4.4mm connectors that you can easily swap out with a screw-lock system.

Sound
Gear used for testing includes the FiiO KA17, HiBy R3 II and xDuoo TA-20 Plus. The FD15 is easy to drive, so it doesn’t need a powerful source but it can scale with a better quality source.
So, about those filters – the black filter is the default option, offering superior detail retrieval and resolution. In contrast, the red filter imparts a warmer sound signature and raises the perceived level of bass. I switched to the red filter for a while (because I like my bass) but eventually went back to the black one because some micro details were missing. Furthermore, the black filter has better clarity and air, ultimately rendering a more open and transparent sound.
The FiiO FD15 has a balanced sound signature. With the black filter, it sounds fairly neutral but with a little enhancement in the bass. Its natural timbre stands out as one of its biggest assets, especially in the midrange and treble. FD15 strikes the right balance between clarity and musicality so that details are well-preserved butt it still has a pleasing tonal quality.

Bass
Just like the mids and treble, the FD15’s bass gets the timbre just right. There’s some sub-bass fall-off but that extra-large dynamic driver can still surprise you with its extension and rumble. Bassheads will likely find the quantity of the lows on the light end of the scale, even with the red filters. For me, however, I find the bass compliments the midrange perfectly, adding depth and warmth.
Midrange
The mids are rich and articulated, silky smooth without being oversaturated. Vocals are slightly forward, with an underlying warmth provided by the mid-bass. This midrange is full-bodied and natural, maintaining excellent clarity. While it may not be the most transparent, it prioritizes naturalness over absolute fidelity. The result is a sultry and engaging sound that is never overly dark nor thick.

Treble
While it’s not particularly forward in the mix, the FD15’s treble has good extension. Despite being slightly laid-back, it’s airy and even a little sparkly. The treble tuning is designed for accurate timbre and overall coherency, providing a neutral but engaging presentation. As a bonus, there’s no harshness in the highs either.
Soundstage & Technicalities
The FiiO FD15 delivers a commanding and wide soundstage. It creates a natural three-dimensional image, that while not the most organized, still maintains a congestion-free zone. Imaging and layering are good, however, detail retrieval is somewhat average, even with the black filters.
Comparisons
FiiO FH3 ($119)

FH3 is more balls-to-the-wall fun than the FD15 but it’s less accurate in timbre and tone. It has a grittier and more boisterous bass with greater sub-bass extension. FH3’s mids have less clarity but its treble is brighter and edgier.
The soundstage has more depth on the FH3 but the FD15 has the edge when it comes to width. FD15 will likely suit more people’s tastes as it’s more refined and smoother up top but those who seek a more visceral bass response might prefer the FH3.
Letshuoer S12 Pro ($135)

The Letshuoer S12 Pro (review here) has a 14.8mm planar driver. It’s more V-shaped and has significantly more elevated lows in both the mid-bass and the sub-bass. If you like earth-shattering sub-bass, the S12 Pro does it better than most planar IEMs.
The timbre is less accurate than the FD15 because the underlying bass permeates the sound and colours the tone. Lower midrange notes are thicker and the core midrange is slightly recessed compared to the FD15’s more forward vocal presentation.
S12 Pro’s treble is smooth and sweet yet surprisingly, its micro detail retrieval is much better than the FiiO. The stage is equally wide on both IEMs but the S12 Pro achieves more stage depth and better layering.

Verdict
The FiiO FD15 is a lovely IEM in terms of build, comfort, and audio quality. It has a lovely tone and accurate timbre that bring music and vocals to life. It’s not for people seeking a powerful, rumbling bass but rather those who appreciate a more balanced presentation. With its excellent included accessories and strong performance, the FD15 stands out as a top recommendation in its price bracket.