Fit and Comfort

The FiiO FH5s is about average in size and weighs slightly more than average at ~8.8 g per ear bud, but you would not really be able to tell because of that excellent ergonomic design I rate as one of the best I have ever had my hands on. I have medium-sized ears, which the artificial ear mold above represents quite well. There are also a ton of ear tips that come with the FH5s, but in general, the fit is excellent with three points of contact at the antihelix, helicis crus, and antitragus while being inset in the concha. Smaller ears might have some issues, but you can play with the fit to where you can have two points of contact to relieve pressure off the third, or go with something like the final Type-E tips that just rest at the entrance of the ear canal, but do note that this shifts the center of gravity further outwards too. The cable provides further support as it goes over and around the ears, and the semi-open design keeps things relatively cool without compromising on sound isolation where it matters.

Audio Performance

Audio Hardware

FiiO uses a hybrid driver setup in its FH series of IEMs, including this new FH5s. This time around, it is a brand-new combination of two dynamic drivers (DD) and a dual-unit balanced armature (BA) driver. The sub-bass and mid-bass is handled by a relatively massive 12 mm beryllium-plated diaphragm dynamic driver with a PU gasket around it, capable of 1.5 T magnetic field strength with the accompanying N52-grade neodymium magnets for what has the potential to provide thumping but detailed bass. More interesting is the replacement of a typical balanced armature driver from the mids and the transition from the lows with a second dynamic driver, which was done to keep the soundstage wide and deep relative to BA drivers that are excellent with transient response but don't really boast on soundstage. This one is a smaller 6 mm beryllium-plated diaphragm dynamic mid-frequency driver catering to vocals and instruments. Last but not least is a Knowles TWFK-30017 dual unit balanced armature driver. It is not new and FiiO could have arguably found better and newer hardware from Knowles itself, but it does have a working history behind it and should be able to handle the high frequencies with proper tuning.

FiiO complemented the driver system with the shell design we discussed before. There is  a video going through the assembly of the FH5s, including the placement of the drivers, wherein you can see details, such as the BA driver placed right in the nozzle (sound tube), and another video going over the use of the semi-open design for balanced pressure throughout as it pertains to comfort and the functioning of the driver, as well as the deliberate choice of using a second dynamic driver for the vocals. So at least on paper with the limited information available, we have a technically competent system. Driving these will take more power than the average IEMs with a rated total impedance of 40 Ω, but not to where a dedicated amp is absolutely necessary. A portable DAC/amp or even DAP might be nice to have on the go, especially with the lack of a 3.5 mm jack on most phones today. If not on the go, space is less of an issue, but the 1.2 m cable might be a potential handicap if connecting to a PC as the audio source. FiiO also rates the signal sensitivity at 106 dB and a frequency response of 10 Hz to 40 kHz.

Frequency Measurement and Burn-in

I will mention that I have a general preference for a warm neutral signature emphasizing a slightly elevated bass and smooth treble range 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 an IEC711 audio coupler/artificial ear that ear buds can feed into enough to where you have 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. Size M silicone ear tips are used for the review unless specified otherwise. Testing begins 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 an ear geometry and not just the audio coupler by itself. The raw data is then exported from REW and plotted in OriginPro for easier comparison.


Talk about a deviation from the norm! Let me provide some context to those wondering what is going on here. Break-in or burn-in periods are, in my opinion, purely psychoacoustic most of the time. There are some genuine factors, including people getting used to the earphones, the ear tips providing a consistent fit, and coming up with the best-working conditions for the source output to the earphones. Wear and tear of drivers of course happens over time, but usually results in worse/looser audio performance. In extremely rare cases, break-in periods can help with the stabilization of the driver system if not tested at the factory.

So imagine my surprise when I saw what should be a nice set of IEMs on paper get poo-poo'd by most reviewers and customers at launch! FiiO then came in claiming 200 hours of break-in is needed with the FH5s, which is far beyond what anyone really has the patience for. In fact, it is so much that I decided to purposely call it a burn-in as this is a brute force approach FiiO should have absolutely done itself before shipping units out. Regardless, here we are actually testing it out. I listened to the FH5s right after unboxing for ~30 min and took a frequency measurement using the balanced size M silicon ear tips before playing a mix of white and pink noise as well as different music playlists for over 250 hours while I went about testing other products. The end result is that there is actually a measurable and audible difference! The lows and mids are basically identical, but the transient response in the treble is much cleaner and more consistent. There are fewer rises and dips, and the post burn-in frequency curve looks an awful lot closer to the one FiiO published on the product page, though keep in mind that my IEC711 audio coupler is not the best after 10 kHz.


What happened here? I initially thought the burn-in period might be related to the diaphragms which need to vibrate consistently like a spring, and perhaps an air-pressure differential needed sorting out over time with the semi-open design. But the frequency regions handled by the two dynamic drivers seem unchanged, and it is the Knowles BA that seems to have changed over time. A look at the driver specifications sheet doesn't reveal much, but it may well be the differential air pressure again working itself out to be completely balanced throughout the shell. The BA is situated right at the sound tube itself, which is also the furthest from the rear cavity/face plate where the semi-open design is located. This is only a hypothesis with no real evidence to bring it close to a theory, but the point remains that there is actually a change here. I don't know if it actually needs 200 hours, and why FiiO did not just do this at the factory is beyond me. As to whether or not you will perceive the change is something I can't answer for you, but I did and all subsequent measurements and tests are post the 250 hour burn-in.