Fit and Comfort

Seen above is the balanced silicone size M ear tip installed on the right ear bud and inserted into an artificial ear mold. I have average-sized ears, and the ear mold seen above about perfectly represents my own experiences. Size M tips are my go-to, and typically silicone unless there just isn't a good fit and mentioned otherwise. In this case, all four tip types worked fairly well to where fit alone wasn't a distinguishing factor between them. The size of the ear buds is on the smaller side of average, and the circular form factor also makes it more like your average TWS ear buds when it comes to the fit and installation. There are still multiple points of contact in the concha when it comes to average human ears, but it's more the relatively light ~7 g mass of each that works with the form factor to make these comfortable to wear. The semi-open nature helps too, and given it is in the rear cavity with a small opening, it's not like you lose out on the seal in the inner ear itself.

Audio Performance

Audio Hardware

I have no experience with the FiiO FD5 at this time, but FiiO certainly makes a big deal about taking from it in a clear manner of trickle-down R&D. The single dynamic driver in the FD3 uses a 12 mm diamond-like carbon (DLC) diaphragm driven by a magnetic setup capable of generating 1.5 T field strength, and you will in fact notice the two ear buds acting like magnets with similar poles pushing each other away in some orientations. A copper-clad aluminium Daikoku voice coil is paired with said diaphragm, and the net result is a relative high sensitivity. We got a sneak peek at this when the sound tube was removed, but the FD3 uses the acoustic prism from the FD5 that seemingly "eliminates high frequency standing waves" to assist in sound decay over time. The semi-open nature of the FD3 has also been discussed in detail already, but merits a mention here since it can strongly affect the sound signature, and comfort/fatigue over time.

Frequency Measurement and Listening

I will mention that I have a general preference for a warm neutral signature, emphasizing a slightly elevated bass and smooth trebles with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


Our reproducible testing methodology begins with a calibrated IEC711 audio coupler/artificial ear that ear buds can feed into enough for decent isolation similar to real ears. The audio coupler feeds into a USB sound card, which in turn goes to a laptop that has ARTA and REW running and the earphones connected to the laptop through the sound card. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/6th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average is taken of the three individual measurements for statistical accuracy. For IEMs, I am also using the ear mold that fits to the audio coupler for a separate test to compare how the IEMs fare when installed in a pinna geometry and not just the audio coupler by itself. The raw data is then exported from REW and plotted in OriginPro for easier comparison.


The IEC711 is such that you can't really compare these results with most other test setups, especially those using a head and torso simulator (HATS). The raw dB numbers are also quite contingent on the set volume, gain levels, and sensitivity of the system. What is more useful information is how the left and right channels work across the rated frequency response in the FiiO FD3, or at least the useful part of it. The left earbud was separately tested from the right one, and colored differently for contrast. I did my best to ensure an identical fit for both inside the IEC711 orifice, so note how the two channels are pretty much spot on most of the way through the bass and mids. It is only at ~5 kHz that there is some minor channel discrepancy before things diverge further past ~12 kHz. This is of course considering that the IEC711 isn't all that reliable at higher frequencies, and I could maybe make out a tiny difference when it comes to triangles in orchestral recordings. Maybe. It's not really a deal breaker by any means, and I will also mention that there was no discernible break-in period or effect this time around, not even after ~250 hours of the IEMs outputting audio signals of various kinds, so at least this time around, we don't have that peculiarity.

A similar trend with consistency continues with the test using the ear mold to represent an ear and cheek simulator and an example set of ear canals. I noticed a natural common point at 1 kHz, relative to which there is the tiniest of drops in the lows and mids with the frequency response. That 8 kHz peak shift is a mix of measurement artifacts and a sign of the treble response getting a bit more jumpy. Before we get to talking more about the sound signature and tuning, I will point out that this page has a lot of measurements that actually show up with changes made to the hardware, and I am as such not including those with the different ear tips (vocal/balanced/bass), but also can't say they made a lot of difference in my listening experience either—at least when it comes to the FD3 with everything else held the same.

I would describe the tuning of the FiiO FD3 as a bright V-shape in that we have a characteristic V-shape with the single dynamic driver playing to its strengths in the mid-bass in particular. There is plenty of sub-bass, but not to where it is a rumbling monster. The bass tips seem to help drive this further, but it is more to do with the smaller bore that, as with the sound tube, results in a smaller volume to then accentuate the lower frequency response. What did surprise me was how relaxing the bass notes felt, which, if going by those I have heard, isn't the typical way a single dynamic driver IEM is tuned. There is slam, but it tucks you into bed comfortably afterwards. There is punch, but through a soft pillow to cushion the blow. I am trying to say that this isn't a set I would necessarily buy for bass solely, with its strength lying more in the lower mids, where the additional warmth plays favorably in lifting up male vocals without losing any range with instruments. The upper mids too are excellent when it comes to pop music in particular, and R&B fans will find this a good pairing for the genre. With higher-pitched sounds, including some female vocals in opera, things sound rushed and somewhat tinny. There is not enough hang time, if you will, until you get to the higher frequencies with cymbals, piano keys, and triangles, where things get better again when it comes to resolution, decay, and impact. Keep in mind that this was all with the default red sound tube that is meant to deliver robust bass, which leaves me wondering what the other sound tube would do.


This is what it would do, clearly. I have normalized the frequency response curves with the two sound tubes at 1 kHz to further see any changes, and the black tube meant to deliver more detailed treble affects the transient response in the highs without affecting the lows or mids. I don't know if increased detail is the phrase I would use here, but it did help with imaging in particular, wherein the use of classical music once again comes in handy. I think the FiiO FD3 can thus be made more suitable for vocals and orchestral music than metal or EDM, and I did listen to quite a lot of Mozart on these as such. The vocal tips didn't really make a tangible difference for me, but they may help your case further.


There are not too many other IEMs in my current possession that operate in the price range of the FiiO FD3, especially if only going with single dynamic driver IEMs. As such, I went with the less expensive BLON BL-A8 and slightly more expensive TinHiFi T5 to give you some idea of where things lie. This is also where graphs can tell you a lot, which subjective preferences may or may not relate to. Objectively, we see slightly more elevation with the sub-bass in particular when comparing the FiiO FD3 to the BL-A8, and the TinHiFi with its target tuning catering to a different market (their words, not mine) is playing checkers while the rest are playing chess. The FD3 then shows a more balanced approach in the mids and highs compared to the other two, and this is where my subjective thoughts came in as mentioned above. Based on my specific interests, I would go with the FiiO FD3 over the other two. FiiO doesn't clarify what the target tuning was supposed to be, except in the form of a frequency curve that pretty much matches mine, so I suppose it should also score high in the context of matching marketed expectations.


Before we conclude our thoughts, here's a quick look at the New K3 in action. It's on par with my reference soundcard when it comes to the music output and drive for the FD3, which isn't really much to say. However, it did help quench some of the tinniness with female vocals when paired with the black sound tube. The bass boost clearly does what you expect, and now, the FD3 truly sounds like a bass monster. The bass boost nets ~6 dB at its peak in the sub-bass and begins at ~600 Hz even though it really is more perceivable from 200–300 Hz and below. This does result in some bleed into the lower mids, which at least on the FD3 is too much of a good thing. It is not shown here, but the gain switch just offsets the entire response north by ~6.5 dB for some more power-hungry headphones. Unfortunately, this is also how I found out that the FD3 doesn't take EQ all that well, including with the bass boost that resulted in an uninspired thump that was going to give me a headache instead of make me listen to music even with the volume turned down. I tried to EQ different regions higher than others, and any more than +/-2 dB will have a detrimental effect on sound quality.