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FLC Technology FLC8s: Is it a bird? Is it a plane? No, it's a Chameleon! - [Review] 🇬🇧


Hierbei handelt es sich um meine englischsprachige Rezension des FLC8s. Die deutsche Variante kann hier gelesen werden:


There are various universal in-ears out there that feature replaceable sound tuning filters that guarantee for a (sometimes more, sometimes less significant) sound alteration to one’s personal preference, but there hasn’t been any that allows for 36 filter combinations – well, at least until now, as the FLC Technology FLC8s does indeed offer three filter groups that can be combined to 36 possible filter combinations.
FLC Technology ( is a Chinese audio company that was founded in 2011 by Forrest Wei. The letters F, L and C (pronounced “Fu Lai Si”) by the way stand for “Happiness/Fortune comes here”. Before FLC, Forrest has worked as engineer at various renowned audio companies for many years (his vita contains Ultimate Ears, Jabra, MWM Acoustics and Harman), and this experience can be indeed heard with his latest creation, the FLC8s. Before this model, FLC Technology offered a custom-moulded hybrid in-ear that offered the same patented filter technology.

What’s quite special about the FLC8s is that unlike many other hybrid in-ears which feature a coaxial driver design layout where the midrange/high frequency drivers sit in front of the dynamic woofer and end in a large single-bore nozzle, Forrest’s creation features an independent dual-bore design that merges before the nozzle, which allows for the individual tuning of the different driver designs.

A sample of the FLC8s In-Ears was provided to me free of charge for the purpose of an honest evaluation. My hearty thanks go to FLC Technology’s Forrest Wei and Lend Me UR Ears for this opportunity.

Technical Specifications:

Price: ~ $349 (
Sensitivity: 107 dB/mW @ 1000 Hz
Frequency Response: 20 Hz – 20 kHz
Drivers: 1x 8.6 mm dynamic, 2x Balanced Armature
Impedance: 11 Ohms
Cable Length: 1.2 m

About Hybrid In-Ears:

As you can read from the technical specifications, the FLC8s is a little different from most In-Ears and doesn’t only use dynamic or Balanced Armature transducers, but combines both in one shell.

Most In-Ears use dynamic transducers for audio playback which have the advantage of covering the whole audible spectrum and achieving a strong bass emphasis without much effort. Valuable dynamic drivers are often said to have a more bodied and musical bass that has a more soft impact and decay and lacks of the analytical character that BA transducers are known for. On the downside, in contrast to headphones with other driver principles, dynamic transducers often have a lower resolution.

Higher-priced and professional IEMs mostly use Balanced Armature transducers, which usually have got a higher resolution than dynamic drivers, are faster, more precise and have got the better high-level stability, which is important for stage musicians that often require higher than average listening levels. On the downside, it is quite hard to cover the whole audible spectrum with just a single BA transducer and strongly emphasised bass is only possible with multiple or big drivers. Some people also find In-Ears with BA transducers to sound too analytical, clinical or cold (in several active years in a German audio community where I wrote multiple reviews, gave dozens of purchase advice and help, from time to time I heard people that got into BA earphones for the first time using these attributes for describing BA earphones, especially their lower frequencies).

Hybrid IEMs unite the positive aspects of both driver principles and use one dynamic transducer for lows reproduction and at least one BA driver for covering mids and highs, wherefore the often as “musical” described bass character remains and the BA transducers add resolution and precision to the mids and highs – and that’s what the FLC8s does with its technology. It is addressed to those people who perceive the clinically-fast character of BA transducers as unnatural, but want to keep the mids’ and highs’ resolution, speed and precision.

Delivery Content:

For me, a valuable product deserves an appropriate packaging, and the FLC definitely does not disappoint in this regard.

On the outside, the slightly larger, surprisingly heavy and sturdy box is rather plain looking with its pale sand colour and the silver logos, but offers a quite interesting and well-thought, unique way to open it, whereon the arrow with the “open here” text in the lower left corner already gives a hint. The front (and all ensuing sides that can be opened) is magnetically attached and can be folded up, kind of like a chest. Then, the in-ears which are embedded in blue foam become visible. Pushing on the foam where the black arrow with the “press to open” text is located, it can be taken out; inside this upper layer are large plastic tweezers and a quick-start guide that explains the filters and gives some combination examples.

On the front, another arrow with “open here” text points to the left side which can be swung open as well, then the whole top layer with the foam can be flipped away to the right side, which is pretty cool in my opinion. Inside the second layer, one can see the blue foam again which embeds the carrying case for the in-ears as well as the small cylinder that contains the filters.
In a plastic bag are a 6.35 to 3.5 mm adapter, a cleaning tool, an airplane adapter, four pairs of black silicone tips, three pairs of white silicone tips (the fourth pair of the white tips is already installed) as well as finally six spare tuning filters for the bass and sub-bass.

Looks, Feels, Build Quality:

The in-ears are available in two colours (red or blue), quite small and made of plastic, which I wouldn’t have noticed if I hadn’t randomly read it somewhere on the internet, as I really thought FLC8s’ bodies were made of metal, as they feel very sturdy, are extremely well varnished (wherefore they appear like they were made of metal) and the used plastic is of very high quality; additionally no glue residues can be found at the part where both body halves are joint.
On the inside are the holes for the sub-bass filters; also on the inside are the side-markers on the bodies as well as on the cable connectors. On the outside, the holes for the bass filters can be found. The filters for the midrange and treble are made of metal and screwed into the nozzle.
Except for the mids/highs filters, the other rubber/plastic filters for the lows are really small and easy to loose, wherefore changing them should be best done with steady hands and when sitting.

The cable is of dark blue colour, replaceable and features the same 2-pin connector system as the Ultimate Ears Triple.Fi 10 (0.75 mm pins). Although it has got the typical, valuable, twisted quad-litz style from the professional audio sector, it is a bit springy (though at the same time quite flexible, nonetheless not as flexible as other twisted cables) and has a cable cinch (chin slider) that sits enormously tight so that it can only be moved with much effort. To top it all, it is quite microphonic, but more about that in the next “Comfort, Isolation” paragraph.

The carrying case is made of metal and I quite like it: although it may not be best suitable for fully portable use, it looks and feels very valuable, massive and has got precisely cut threads. The outside has a really beautiful gunmetal-blue finish and is completely bolstered with fabric on the inside (which is in my opinion a must for every in-ear case – I can’t stand bare plastic or metal on the inside of a protection case), so the in-ears are well protected.
The small blue cylinder with the keychain for the tuning filters strongly reminds me of the one that came with my Shure SE846, however the blue one of the FLC8s has got the benefit that the filter elements are stuck into a block of rubber, so it is less easy to lose the seven pairs which are inside (the three others are in the in-ears themselves).

Comfort, Isolation:

The in-ears are actually quite small and are easy to insert into the ears; then they sit very securely and comfortably, whereto the cable connector’s angle also plays a leading role. With my large ears, I have almost never problems with the fit of in-ears anyway, so these sit extremely well in my ears, too – but even most people with (very) small ears should be able to get a really good fit and comfort with the FLC8s.

Like most models in this price range, the in-ears are supposed to be worn with the cables over the ears which usually improves fit as well as comfort and drastically reduces microphonics – unfortunately the latter is not true in this case, as FLC8s’ cable is quite microphonic for a model of its kind and transports cable noise with every small touch or movement – pity! Tightening the cable cinch behind the head and then guiding the cable over the shoulder, microphonics are slightly reduced, however still obviously stronger than they are supposed to be.

Isolation is better than average, however not as strong as with fully closed in-ears. Nonetheless, exterior noise is blocked out somewhat more than with many vented in-ears.


For testing, the source devices I used were the iBasso DX90, Leckerton UHA-6S.MKII, FiiO X3 (first generation) as well as LH Labs Geek Out IEM 100. Music material was mainly stored in FLAC format (lossless rips of my CDs in 16 Bit/44.1 kHz), but I also used Hi-Res, DSD and some MP3 files.
I used the largest included white silicone tips for listening.


The major question I had to deal with while testing was “how do I best describe an in-ear that allows for up to 36 different sound signatures by using different filter configurations?”.
My decision was then to first describe all filters and their effect individually and then finally to give a couple of different sound descriptions of a few filter combinations.

Overall there are 10 pairs of filters that can be summarised in three groups that alter other frequency ranges, wherefore up to 36 different sound characteristics are possible (3 x 3 x 4 = 36). Included are three pairs for the sub-bass (“ULF”) that are inserted on the inner side of the bodies, three pairs for the bass (“LF”) that are inserted on the outside as well as four pairs that are screwed into the nozzle and have an effect on the midrange and treble (“MF/HF”).

The different filters listed in tabular form:


Clear = Minimum
Clear = Minimum
Blue = Minimum HF
Grey = Medium
Grey = Medium
Gunmetal = Medium MF & HF
Red = Maximum
Black = Maximum
Green = Medium MF & Maximum HF

Gold = Maximum MF & Medium HF

Ensuing are a few frequency response measurements of the different filters and the effect that they have on the frequency response. The plots’ colours also represent the filters’ colours.
Please note that the plots weren’t recorded with professional equipment but with my Vibro Veritas coupler that was pseudo-calibrated to more or less match a real IEC 711 coupler’s response with applied diffuse-field target, hence the results shouldn’t be regarded as absolute values but rather as a rough comparison and for getting a general idea of the sound. Especially at 3, 6 and 9 kHz, there are sometimes greater deviations from professional plots, but for a general, rough comparison between various in-ears and filters, the results are sufficient.

(ULF Filter  I  Grey  I  Gold)

(Grey  I  LF Filter  I  Gold)

(Grey  I  Grey  I  MF/HF Filter)

With these in-ears, the focus lays obviously on the ability of individual sound adjustment with the help of the included filters that can form up to 36 (3 x 3 x 4) different combinations and sound signatures. For changing the filters, large plastic tweezers come included. For daily use, I found using my short fingernails (less than 0.5 mm) to be more helpful for changing the filters, as that gave me better control over the filigree things and they also slipped out of my hands way less often, nonetheless it is quite a fiddling to get them in and out. Probably smaller, rubberised tweezers would be more practical.

What follows now is a small selection of different filter combinations that are displayed in this form: [ULF]/[LF]/[MF/HF]

01: Grey/Grey/Gold:
This is the filter combination the in-ears arrived with.
The sound signature of it goes like this: down from 500 Hz, the bass emphasis which raises very evenly and flat begins and forms its climax which is about 6 dB north of neutral sound (Etymotic ER-4S) below 100 Hz, in the midbass; sub- and midbass are even plus plane and also in the sub-bass below 30 Hz, level doesn’t roll off. Given that, the bass is present, however definitely not over-accentuated and fits in coherently, as there is no unnecessary fundamental tone bloom.
The mids around 1 kHz are broad-banded emphasised, with a somewhat greater focus on the upper mids, bringing out (especially female) vocals’ details a bit more, but also slightly accentuating sibilants if the recording isn’t super clean. Tonally, the mids are mostly correct in my ears, with just a minimal tendency to brightness (for reference, DN-2000J’s mids are minimally brighter than FLC8s’ in my ears). From the presence area above 2 kHz on, level drops evenly and forms a greater recession around 5 kHz which guarantees for good long-term listenability without fatigue and with unobtrusive mids; that’s why many in-ears show a somewhat similarly distinctive dip around 5 kHz, for example the Fischer Amps FA-3E whose dip in the middle treble is about identical to FLC8s’ (a good thing is that it isn’t as distinctive as W4R’s dip which adds a bit too much smoothness and relaxedness to the highs and mids with a tendency to mugginess; FLC8s’ middle treble character is just “normal with a somewhat relaxed, non-obtrusive character” and clean plus detailed). From 6.5 kHz on, level starts increasing again and forms a peak in the upper treble at 8 kHz which is marginally above the ground-line and not annoying at all. Super treble extension is still good, with even level up to 12 kHz and an even roll-off from there on. Subtle “glare” above 10 kHz is still audible and I actually don’t miss anything in terms of treble extension, although there are some multi-BA in-ears that reach even higher in the treble before the roll-off begins.
For daily use, this kind of tuning appeared to be quite enjoyable – the bass is somewhat accentuated but not too much to become obtrusive, but is just there to add a little weight, vocals come through very clearly due to the moderate emphasis and sound very clean, the somewhat recessed level in the middle treble guarantees for a good long-term listenability without fatigue and the slight emphasis in the upper treble is just lightly noticeable, though percussions sound slightly brighter.

02: Grey/Clear/Blue:
With this filter combination, I would describe the sound as quite neutral with smooth, dark treble.
The bass is slightly more present than with a Clear/Clear/MF-HF combination (ca. 2 dB north of neutral below 80 Hz), though the benefit is that it doesn’t roll off in the sub-bass with this filter combination. Here, the mids show a slight broad-banded emphasis, too, though there is no emphasis in the upper midrange and vocals are on the darker as well as more relaxed side, without any signs of sibilance. The middle treble is somewhat in the background as well, though even a bit more than with the gold MF/HF filter, so the impression of a smooth, relaxed midrange and treble is even stronger (for my personal preference, it is even slightly too relaxed and heads into Westone W4R’s smoothness in the upper frequencies). The upper treble is now also clearly in the background and darkens the sound.
If you love a balanced bass and midrange with a downwards-slope in the highs, this tuning might be for you.

03: Red/Black/Blue:
With this filter combination, sound is an evenly down-sloping curve from the sub-bass to the upper treble and slightly reminds me of the reference curve for car-hi-fi.
Again, the emphasis in the lows starts at around 500 Hz and then increases very evenly with a straight line, without any hump, towards sub-bass where level is about 9.5 dB north of neutral at 30 Hz. The midbass is a bit less present and so is the upper bass with about 5.5 dB, with an evenly decreasing fundamental tone area. As a result of this characteristic, the bass fits in nicely and unobtrusively, without too much upper bass kick or fundamental bloom, as the emphasis is mainly in the mid- and sub-bass. Accordingly, the lows also commendably stay away from the mids.
The midrange is not slightly emphasised anymore here with this filter configuration and is, just like with the previous Grey/Clear/Blue filter combination, somewhat on the dark, relaxed side. Treble is identical to the previous tuning.
For a smooth, relaxed, bass-emphasised tuning with “cellar rumble”, this tuning is well-suited.

04: Red/Grey/Gold:
This filter combination focusses more on the sub-bass, along with bringing a detailed midrange and correct treble into the game.
The lows more or less resemble the previous Red/Black/Blue filter combination, however with this Red/Grey/Gold configuration, the sub-bass shows to advantage more as both the root as well as upper bass are slightly less present. The bass kicks a bit less and concentrates more on the “cellar rumble”.
The mids around 1 kHz are just very minimally lifted and sound tonally correct in my ears.
The middle treble is about identically in the background as with the first (Grey/Grey/Gold) combination and gives some smoothness and good long-term listenability without fatigue. The upper treble sounds quite natural and as well as not emphasised, but straight to the point.
For a sound with balanced midrange and treble plus elevated sub-bass with less upper bass and fundamental tone, this filter combination works very well.

05: Red/Black/Green:
With this filter combination, the sound of the in-ears follows a v-shape.
The bass is quite identical with the third filter configuration (Red/Black/Blue) and expresses itself with a somewhat emphasised “regular” low-range with upper bass and fundamental tone area, with the greatest focus being in the sub-bass.
The mids around 1 kHz are just very marginally emphasised and in total view, when incorporating lows and highs, vocals are even a bit in the background and also sound somewhat thin, however neither hollow nor low resolving.
The middle treble is audible less in the background with the green filter; the upper treble at 8 kHz shows a distinct peak which is however still humane and not too sizzling or piercing as long as one isn’t listening at very loud volume levels. Nonetheless, sibilance is more emphasised and some recordings get the tendency to be a bit annoying and hot.
For lovers of v-shaped signatures, this filter combination might be well-suited.

06: Clear/Clear/Gold:
This filter combination is one of the recommended in the quick-start guide and is labelled as “Vocal” – for reason, as it really is a signature that focusses on voices.
The bass is rather lean and mostly neutral, at least in the upper midbass, upper bass as well as lower and upper root area. In the middle fundamental tone, there is a minor emphasis; the bass starts evenly rolling off from about 50 Hz.
The mids are in the foreground with this tuning, with a preference of the upper midrange, wherefore this filter combination is well-suited for female vocals. Male singers however sound a bit thin.
The treble is identical to the first (Grey/Grey/Gold) tuning.
For tracks with mainly female singers, this tuning is recommendable if one wants to bring out the voices some more.

07: Grey/Clear/Gunmetal:
This is the filter combination that I see as reference tuning for the FLC8s, and as somebody who loves neutral sound and sees the Etymotic ER-4s as the best example of how neutral tonality should be (the ER-4S is even closer to ideal neutrality than my custom-moulded UERM), I can also say that the FLC sounds pretty neutral with this filter combination and comes quite close to ER-4S’ tonal tuning.
Upper bass, midbass plus the lower fundamental tone are very marginally more present than with a Clear/Clear/Gunmetal combination which however suffers from a moderate sub-bass roll-off, wherefore I see the Grey/Clear/Gunmetal filter combination as the more reference-like. Otherwise sound is free from any unnecessary warmth and the bass is very even, “flat”, without real emphasis.
The mids are pretty spot-on and tonally correct in my ears, without colouration.
The middle treble is somewhat in the background as well, however very slightly less than with the gold filter and therefore seems a bit less relaxed. With this filter combination, the upper treble is also just very slightly, though inconspicuously above the ground-line.
For a rather sterile, very neutral sound, this filter combination is quite ideal (and I personally love it).

For the following comparisons, I used the first and seventh filter combination most of the time.


The resolution capabilities of this in-ear are simply stunningly high for the price and I go that far to say that the FLC8s can compete with my UERM in the midrange and treble department without problems. In the highs, the UE is very slightly more differentiated plus refined and also a bit more realistic despite its peak (in comparison, the FLC sounds slightly constrained/dull in the upper treble), but in the mids both in-ears are about on-par and honestly speaking the FLC8s sounds even more detailed in the vocal area, as it reveals more minute details while sounding very easy-going, precise and natural. Even after about two months of almost daily use, these in-ears still manage to positively impress me with their very good technical capabilities and detailed, silky midrange. Tiny details in the treble and mids are no problem for the FLC8s and fine details are presented and revealed in a very easy-going, natural way. I guess I don’t even have to mention that speech intelligibility is extremely high, as that should be clear from the context.
In the lows, it looks a bit different, but that is simply because of the different driver types: although FLC8s’ bass is very fast and precise, it doesn’t reach the precision, control and details of UERM’s Balanced Armature driver when very fast and complex tracks are being played. FLC8s’ bass character is quite typical for a (really good) dynamic driver and it is not too hard to tell that it is no BA woofer, but on the other hand, this dynamic woofer driver is very detailed on its own and sometimes, especially with less complex and rather slow music, it is quite difficult to say whether it is a dynamic or BA driver, although the bass doesn’t stand in the room straight to the point but is a bit more space-filling.
What Forrest Wei has created hare is a really detailed, technically very capable and brilliant in-ear that has enormous cohesion between the three drivers which harmonise perfectly together, so that the dynamic driver fits in perfectly and doesn’t appear even at the slightest negatively but just somewhat more corporeal and less “sterile”.


The sole area where the FLC8s could yet fail is the soundstage, but it also copes with this discipline with ease: FLC8s’ soundstage is quite large in terms of lateral expansion and about comparable with the one of my UERM. Therefore, width is also somewhat wider than DN-2000J’s stage (though not by much). There is also a good amount of depth, though it is just about one quarter less distinct than width, wherefore soundstage isn’t as deep/almost bottomless like the DUNU’s or UE’s. When it is about three-dimensional presentation and naturalness, the FLC leaves a very positive impression and sounds harmonious.
Regarding instrument separation and spatial precision, the in-ears are technically really strong, as single elements, even if they are yet so small, are super precisely separated – almost as precisely as with the UERM. And as a result, the FLC8s even manages to separate and place instruments slightly more precisely than the DN-2000J which already does a really good job here.


In Comparison with other Hybrid In-Ears with three-Drivers-three-Ways-Configuration:

Oriveti Primacy:
The Oriveti Primacy is a really good and convincing hybrid in-ear with a smooth yet detailed and (in a very positive way) non-exciting sound as well as superb build quality. When it is about sonic strengths, the Primacy comes very close to the DN-2000J, which speaks for its sound quality. However, the FLC8s manages to unveil even more details in the midrange and treble, in addition FLC’s dynamic woofer is even better and more cohesively integrated to the system as it is almost just as good as its two brilliant BA drivers for the mids/highs (Primacy’s lows are very slightly less detailed than its mids and highs although sound is harmonious and coherent, too).
FLC8s’ soundstage is a bit wider than Oriveti’s and has especially got somewhat more depth. In terms of instrument separation, -placement as well as spatial precision, the FLC is also the winner.

DUNU DN_2000J:
The DN-2000J is an extremely good in-ear and convinces inter alia with its special bass which is both very fast and precise as well as tactile and has a gorgeous body at the same time (its lows’ qualities are quite similar to my Audeze LCD-X’s). On top, midrange and treble resolution are excellent.
Well, the FLC8s reveals even a bit more details than the DUNU and also has got a minimally faster bass which is more arid too, although DN-2000J’s is already really good for a hybrid in-ear. What the FLC however doesn’t adopt is DUNU’s woofer’s special character which is albeit something very unique for itself – in exchange, FLC8s is overall sonically and technically the somewhat better and slightly more refined, detailed in-ear.
FLC8s’ soundstage is a bit wider than DUNU’s, however less deep. In terms of spatial presentation and instrument separation, the FLC is somewhat more precise, with instruments that are very cleanly placed and sharply separated from each other – even more than DN-2000J’s.

UPQ Q-music QE80 (OEM Version of the Fidue A83):
Without any doubt, the FLC8s is the more versatile IEM with its theoretically possible 36 different tonal tunings, but will always have less fundamental warmth than the QE80.
The FLC, of which I think is overall very slightly better than the DUNU, also surpasses the UPQ. The FLC8s has got the faster and more arid lows than the QE80, which on the other hand puts out the nicer bass body (this however goes at the expense of speed). When it is about resolution, the FLC is somewhat better as well, even in the midrange.
Solely QE80’s upper treble sounds a bit more natural and realistic as it is more broad-banded.
The FLC’s soundstage is slightly wider, with about identical depth. In terms of spatial precision, the in-ear with 36 faces wins as well.
Victory (however not a big one) of the FLC8s in every aspect expect for upper treble naturalness.


The FLC8s is not only an extremely good hybrid in-ear but also definitely a hybrid flagship. The in-ears are very convincing with their precision, soundstage, resolution (especially in the midrange – vocals sound so clear, detailed and realistic that they even slightly beat my UERM’s) as well as versatility. Surely the knowledge of having 36 potential sound signatures is really cool, however realistically seen, one will more likely have up to four filter combinations that are probably slightly tweaked from time to time. One also has to be careful with the any filigree filters, as they can be lost easily given how small they are – in this regard the FLC8s is more an in-ear for enthusiasts than a product that is suitable for the masses, but I personally find it good that way as it shows how much is technically possible with the various filters.
What unfortunately doesn’t fit to the sound which can be almost seen as being on the same level as the UERM is the cable which is very microphonic for a model of its kind.

Sonically this in-ear scores 5 out of 5 stars with brilliant ease – with a 70%-sound-to-30%-rest-weighting however, the FLC8s “only” manages to score 4.5 out of 5 stars, which is quite sad, as with a less microphonic but more flexible cable, this would be unquestionably a 5/5 product. But even so, the in-ears get a really distinct recommendation for their sonic qualities and two thumbs up.