FiiO FD15 IEM Review – Big Woofer Energy

FiiO’s latest entry in the dynamic driver IEM genre wows with dynamics and a sound signature that makes them a standout in the market.

Introduction

The FD15 is FiiO’s flagship dynamic driver IEM and replaces the former FD5. And it doesn’t cost four figures like some flagships, only 160EUR/$149.99 and FiiO’s best in the genre is yours. It still remains to be heard whether FiiO can cause trouble to other single-driver specialists like Simgot but on paper, there’s a lot to be excited about.

Despite becoming a bit more affordable than its predecessor, the FD15 offers more. A gargantuan 13.8mm driver is now handling all of the audible range which makes it one of the largest dynamic drivers out there. The porting in the front is quite traditional whilst the back features FiiO’s proprietary Tesla valve tech. Your guess is as good as mine what benefits does that bring?

Size does matter in audio but going big often comes with big compromises. Can FiiO design around them? Read on to find out!

Specifications

Physical Things and Usability

Build quality

The FiiO FD15 is made out of solid stainless steel. Not something you see every day, right? The result is an extremely solid, yet heavy shell that feels nice in the hand and okay in the ear. At 12g per side, the FD15 weigh twice as much as many chunky acrylic flagships with 10 drivers inside. The steel is also magnetically conductive so often both IEMs would stick together. I’d also caution against using them in an environment where magnetic metal particles are present.

Each shell has a removable nozzle that screws on and has a retaining lip for a more secure eartip retention. The cable sports pretty fancy Furukawa monocrystalline silver-plated copper wires in a paracord braid. Ergonomically I have no qualms about it and as it’s my only MMCX cable, no comparisons could be done at that point. The swappable tips are a bit hard to remove from the 4-pin connector because the connection creates a vacuum pocket inside the barrel.

Eartips

As is customary with FiiO IEMs, the FD15 comes with a truckload. The two foamies are pretty self-explanatory, while the four other pairs each come with a flavor – be it vocals, bass, or nothing (balanced). The HS18 tips felt pretty okay to me and I felt them to be a bit dark due to the narrow bore. Most of my listening was done with the wider-bore “bass” tips as they did the exact opposite to me – added extra zing and imaging due to the wider opening. Overall – good job with the tips, I couldn’t find a combo that I wouldn’t like.

Sound quality and signature

Test setup: On the go, I used my Qudelix 5K and FiiO Q15, while desktop use was tested mostly on the FiiO K11 R2R and SMSL SH-X combo.

Most of my listening was done with the black nozzle with the red seal which FiiO describe as giving a more “emotional experience”. The other nozzle with the black seal is brighter with about +2dB rise over 5kHz. It’s certainly more analytical and might even be preferred by some but to me, the “emotional” nozzle enhanced more of what the FD15 is capable of. I’ll add that like many other single-DD IEMs, the FD15 is quite sensitive to hissy outputs due to its 128dB/V sensitivity.

The basic sonic character of the FiiO FD15 is a tad laid back, and dark but supremely dynamic! In many ways, it reminded me of listening to a good big-woofer speaker system where lows are handled by a nice 15″ paper cone. There’s no two ways about it that the FD15 isn’t entirely neutral with a tad too little ear-gain and about two resonant peaks at 7.5kHz and around 10kHz but for most of my listening, I found them pretty benign.

The effective area for a 10mm driver is around 78.5 square millimeters. Want to know how much it is for a 13.8mm? Almost twice that at 149.5 square millimeters. This means that at an equal SPL and frequency, the FD15 driver has to work only half as hard compared to the more common 10mm driver. I’m half certain that it’s the secret behind the bomblike dynamics on display here. And of course, a bit less ear-gain means that one can crank the FiiO FD15 without it sounding loud.

Despite the coloration I found the FD15 to work very nicely with a wide array of music. Classical and not-so-classical rock works wonders with the mid-bass-centered low-end and the mids are superbly liquid. As with other single-DD IEMs, the coherence is superb with no frequency range sticking out. Another standout was death metal and industrial music which was more listenable with the slightly subdued upper mids. For electronica, there was always enough extension.

Select comparisons

Simgot EA1000
The EA1000 is probably Simgot’s opus manga in the single DD genre. It can be found for around 175 bucks on Amazon thus putting it head to head with FiiO’s latest dynamic driver IEM. Kit-wise I can’t really fault any of the two offerings with the FD15 being more versatile in its eartip choice. I have to also note that the EA1000 only really worked for me with the golden tuning nozzles while for the FD15 both sets added something.

In terms of fundamental tuning both of the IEMs couldn’t be more different. The EA1000 is a technicalities monster with a tuning that’s a bit on the bright side. Pair it with a clinical source or amp and there’s a good chance it will only be listenable with minimalistic genres like jazz and some IDM. The FiiO FD15 is its opposite or the perfect companion – it puts boogie over brains and I can’t help but start headbanging with them.

Pairing notes

It was hard to achieve a suboptimal pairing with the gear I have here. My favorite is the FiiO K11 R2R with a decent solid-state amp but even the Qudelix 5k did reasonably well. I’d only caution against pairing the FD15 with an overly warm-sounding signal chain and one that’s either hissy or incapable of going into negative gain.

Concluding Remarks

FiiO’s newest dynamic flagship IEM succeeds by offering a fun specialist tuning that stands out from the rest. For some, it will be a great first IEM but most will appreciate how complimentary it can be to others. The swappable nozzles offer two worthwhile flavors of which the darker one is the most unique. Both retain the gorgeous mids and superb dynamics that make the FD15 a standout in the market and an easy recommendation!

My verdict – 4/5