The best way to start discussing what it sounds like is with the default filter setup. The out of the box setup is a grey thin filter for the LF and a red sealed plug for the ULF. The final filter is the gold screw-in MF/HF filter. Together this combo is designed for maximum sub-bass output, medium bass output, plenty of mids and a neutral high-frequency response from the FLC 8s.
With the red ULF filter, you are getting something like a 10dB differential from the other two plugs with a clear focus on the 20-80Hz response region responsible for rumble, depth, and power in the FLC 8s signature.
It is perhaps my favorite filter so perhaps the red in the unit by default was not a mistake in my case. I love how the red filter’s complete seal really beefs up the dynamic driver’s response but at the same time doesn’t overly warm the signature beyond that response region.
The use of the grey LF filter tempers the 80-300Hz region with a small amount of elevation so it is not as dipped or neutral as the clear filter but not as warm and thick sounding as the black filter. With the red/grey low combo, you get a clean, powerful low end with a neutral amount of mid-bass warmth to keep instrumental notes from sounding overly thin or lacking in texture.
The gold MF/HF provides a fairly sustained but plateaued lift in the frequency response starting just above 1k and staying very linear and even right the way throughout to 5k before rolling off from 6-10k and a gentle bump thereafter. The concept of this filter is to provide an energetic focus on the mids and a complementary but slightly laid back treble response.
And it works very nicely indeed with a smooth and slightly forward vocal presence matched with some decent but not overpowering upper mids percussive snap. Timbre is neutral to natural in its delivery with a clean attack and a quick decay.
Treble retains a clean and somewhat natural sounding tonal response that never gets too harsh or brittle sounding. I must emphasize though this is not overly rounded or shelved down in its tuning. The FLC 8s gold filter is not a dark signature, just not a dominant top end or with a ton of sparkle.
FLC Technology helpfully provides a further 6 combinations with a various tonal bias for certain genres or types of signatures so we can use this as a useful guide on discussing further sound impressions.
For a more prominent vocal presence, FLC recommend a combination of the Clear LF, Clear ULF, and the gold MF/HF filters. This will drop both the sub-bass and bass level to their lowest possible setting, a full 10dB approximately lower than the Red Filter from 20-80Hz and around 6-7dB lower than the max LF filter (black) from around 80-300Hz.
Clear ULF and LF Filters
Note the FLC 8s curve is much the same as the stock in terms of bias, with a gentle u-shape. Rather, with the clear filters, the dB elevation across the low-end to lower mids is much lower. You are going to hear a leaner and less impactful bass response which will draw a bit more focus on the gold filters elevated mids presence.
I just want to note though the bass response is much more neutral I do not find it overly lean or brittle. It still has a gentle lift with a little warmth. Combined with the very smooth sounding gold filter the tonality is far from sterile or analytical in its signature.
Golf Filter Influence
With this combination, you get an altogether more mid-centric and flatter presentation with less depth and more energy in the mid to upper-mid performance. The retention of the gold filter means you do retain that smooth and easy going top end but the focus is much more on the slightly elevated vocal presence.
When I say vocals there is a slight bias to higher pitched vocals with the energetic lift starting around 1-2k as opposed to 800-1k so female vocals generally tend to benefit a bit more. It will also project a slightly more intimate staging quality with less depth than the stock filter combo.
It is somewhat surprising this was not the out of the box config as I generally tend to think balanced as default. With the combo you are working with the grey LF, grey ULF and gunmetal MF/LF denoting a medium or “balanced” config right throughout the range. Nothing should be overly dominant.
This is a fantastic presentation and perhaps one of my favorites out of the recommended combinations. Back comes a little additional bass depth (approximately 5dB) and warmth though with the grey ULF you won’t get the full power of the red sealed ULF.
Bass is better balanced though in my opinion with decent power, impact and most importantly that natural dynamic driver sound. It is an altogether more coherent low to lower mids presentation.
Vocal presence for me is still quite good but the additional spacing created with the better sense of depth provides for a bit more of an involving and 3-dimensional presentation than the vocal combination. My own preference for vocals would gravitate to the balanced combination. Sometimes a mids focus can rob the music of PRaT which the balanced successfully avoids.
Instrumental timbre is still smooth sounding though slightly less neutral with a bit more body and richness than the clear LF provided in the lower mids. The gunmetal filter also retains that smooth sound of the gold filter on the mids which I really like but adds a bit more sparkle around 5-7k than the more leveled off gold presentation. This gives a little more perceptible headroom and air to the FLC 8s presentation.
Piano & String Music
For piano and string, FLC recommends the use of a clear ULF, clear LF and a green MF/HF combination. This means your FLC 8s is tuned for a low amount of sub-bass and bass and a reasonably decent mids and stronger high-end. In fact, the green filter is listed as having the most forward treble of the three.
Right away this filter combination is not going to work with any bright recordings or rock music. It creates too much of an ethereal or light bodied presentation with just a gentle bass presence and a heavy focus on the mids and top end with the green filters providing plenty of treble energy. You get better headroom and air but it does lack a bit of depth.
Piano and string really translate into acoustics and small ensemble piano passages with a sparse and black background. It is incredibly fast with the balanced armatures featuring more heavily than the dynamic driver. This is pretty much what you need if you want to pick up and hear every pluck, splash, and reverberation.
Acoustic guitar work is excellent with a very accurate timbre. This is neutral in many respects but thankfully avoiding sounding brittle. Vocal presence is still forward for my ears which I prefer.
Percussion work and partial overtones are a little brighter with an odd harmonic bias drifting in from the green’s perkier treble response which has the most pronounced 7k elevation out of all the filters.
Pop & Rap
To achieve this mix FLC recommends using the black LF, grey ULF, and the gunmetal MF/HF filter set. In theory, this should give you about 5dB additional sub-bass but with more elevation and warmth in the 80-300Hz midbass response. The Gunmetal filter should produce a fairly balanced mid and top end response.
Black LF & Grey ULF
The resulting combination, given the stock FR of the FLC 8s, should give a gentle musical u-shape response. There is a slight sub-bass roll-off below 80Hz so there isn’t a huge rumble like you can achieve with the red filter. Instead, the focus is more on a warmer elevated 80-300Hz mid-bass response adding some fullness and impact essential for modern pop and most dancefloor music. You will get a touch more bleed into the lower mids with this combo though but it is not bloated sounding.
Mids are generally excellent with the gunmetal delivering a neutral to natural sounding timbre and excellent vocal presence, especially for female vocals. I do slightly prefer the balanced combo for vocal positioning and less mid-bass bias but this works nicely for EDM and anything that requires a stronger level of PRaT.
Top end sparkle is more prominent around the 5-7k range than the gold filter but not as forward sounding or sharp as the green filter. There is nice harmonic balance on the gunmetal filter with the gold erring slightly to even and green to odd. Again, all very necessary for EDM which tends to feed off airier presentations with more treble presence.
I am not sure what light music really is these days – Little River Band perhaps? Oops, gave my age away there. Anyway, to achieve this FL recommend you use Clear LF, Clear ULF and the gunmetal MF/HF set of filters.
Clear LF and ULF
This will takes away the majority of the bass response leaving everything relatively neutral and linear sounding with only a slight injection of warmth and elevation to prevent it coming across as overly anemic.
The gunmetal filter will also dial back the mids a touch to a more neutral yet still smooth sounding and accurate timbre and vocal position. The treble is also relatively neutral though unlike other combinations this one will have a bit more focus because of the lack of bass and relatively neutral mid-range providing less of a contrast. Here the focus is more on an odd harmonic signature with clean fast attack and a leaner note with a more prominent top end.
This was perhaps my least favorite combination. Not least because honestly I do not have anything you could term light music I enjoy listening to but mostly the staging lacked any sense of depth and power which I tend to prefer. Overall a slightly dull combination.
To set up for the classical experience FLC recommends using the grey LF, Red ULF and the green MF/HF filter combination on your FLC 8s.
This combination will maximize the sub-bass response, produce a ‘medium level’ of mid-bass elevation and warmth, a neutral mid-range and a more forward sounding top end. In short, this is close enough to call a V-shaped response.
Red ULF and Grey LF Filters
Again, with the red filter you get an approximately 10dB increase in sub-bass power from 20-80Hz to generate that excellent power that dynamic driver of the FLC 8s is capable of. The 80-300Hz mild elevation of the grey filter retains a nice sense of fullness and moderate levels of warmth and richness in the 8s note body.
Its a strong driving bass response with plenty of PRaT. With the red/grey low combo, you get a clean, powerful low end with a neutral amount of mid-bass warmth to keep instrumental notes from sounding overly thin or lacking in texture.
Green MF/HF Filter
This filter is built for speed and first raised its head as a specialist for piano and string and I can well see why it would be a natural choice for classical music. The red and grey filters give you that sense of depth and impact but it is the green filter that keeps everything very nicely separated and very clear sounding.
It is not the thickest sounding filter but that’s perfectly fine as complex string ensembles have excellent clarity and control. Vocals will sound a bit recessed in comparison to the stronger treble and bass performance so it is not the best ensemble for vocal excellence. If we discuss classical music with this filter set it is not going to include operatic vocals but a full-scale orchestral performance.
The FLC 8s is rated at 11Ω and 107dB sensitivity. Overall this is a very easy IEM to drive out of either smartphone or DAP though personally I prefer a natural sounding DAP with a good amp signal for the best possible dynamic range and snap from the dynamic driver, especially if I am using the red filter.
That being said the FLC 8s is one of the more sensitive IEMs out there so whilst the results from weaker sources are pleasing, higher noise floors will show up quicker with some showing background hiss similar to the Andromeda and SE846.
DAPs such as the DX200 with AMP 1 and the X7ii with AM3a behaved very well indeed with very quiet noise floors on both.
The Cayin i5 pair very well indeed with the FLC 8s and much work has been done to control the noise floor with the i5 amp output but it is not 100% quiet with the 8s. The noise level is actually very minor though but it is the first time I have picked up a hint of noise on the i5 in a while.
The FiiO X5ii noise level was actually much higher than the Cayin i5 when paired with the FLC 8s so you won’t get a black background with this pairing.
Hiss on the Alien Gold Plus Edition was beyond acceptable parameters, to be honest even if the tonal pairing was a smooth and rich sounding experience.
There is literally nothing that can compare to the FLC 8s in terms of complex filtering systems for 3 different areas of the frequency response. However, we have come across filter based IEMs before at similar prices.
Trinity Audio Icarus III
I reviewed the Master 4 before but personally, it can’t hold a candle to the FLC 8s despite offering up to 7 different tuning combinations. It is much more in the budget range sound wise despite its push-pull quad driver configuration. Much closer competitively speaking is their higher end Icarus III which we will have a review out in the coming weeks.
The Icarus III (I3) is a 2 BA + 1 Dynamic Driver Hybrid IEM with an unknown level of output resistance and sensitivity level. I say unknown simply because I have searched high and low and can find nothing specific leading me to think that was intentional. What I can say is that it is harder to drive than the FLC 8s. Even on DAPs, you are talking a good 10-15 digital step difference in low-gain mode using the likes of the AM3a amp module from the X7ii.
The I3 uses a color-coded filtering system with 6 different colors. The important thing to note is that each color is duplicated due to the use of a damping system in the 6 duplicates. They are fairly easy to differentiate simply by looking at the back where one has a filter inside and the other does not. The damper is generally a treble smoothing technique on these filters so the damper versions will have a slightly top end attenuation in comparison to the other set.
The filters are not as complex as the FLC 8s. Whilst they focus on similar final outcomes such as enhanced bass, balanced sound, V-shape, and treble focused they are set in their configuration.
What this means is that unlike the FLC 8s you have no independent control over sub-bass, bass, mids or treble. What you get is a fixed sound with each filter. Generally speaking, that’s the unique aspect of the FLC 8s that no one else is doing.
In defense of the I3, the filters are so much easier to work with. Having just one filter screwed into the nozzle much like the MF/HF filter of the FLC 8s is a breeze to change and much less likely to get lost. With the FLC 8s, it is only a matter of time before you email support for spares.
Given the difficulty of comparing 12 variations against 36, the easiest is to set each one up with their balanced filtering and compare. Immediately the FLC 8s sounds more resolving, more open with superior depth and delivering a more holographic staging quality than the I3. The difference between these two is stark.
The I3 in comparison sound flatter and narrower with a top end that doesn’t deliver as much air or spaciousness as the FLC 8s. Both are neutral to natural as you would expect with balanced configs but the I3 seems slightly less weighted in the sub-bass with a bit more mid-bass warmth than the FLC 8s.
Lower mids on the I3 are a little thicker and rounded sounding and treble is definitely a lot more rolled off than the FLC 8s.
Vocals on the I3 are a little further forward, especially for male vocals but they are not as detailed sounding as the FLC 8s and suffer from the lack of top end air with the 8s sounding effortless in comparison.
The T10 was the first in RHA’s premium lineup of metal injected molding IEMs. This is a single dynamic driver rated at 16Ω at 100dB so it is not as efficient and as easy to drive as the FLC 8s but it is not the hardest in the world to drive from a good DAP. Note hiss from higher noise floors will show up quicker on the FLC 8s than the RHA T10
The T10 weighs a bit more due to that robust metal chassis and has a beautiful look. The FLC 8s is much lighter in comparison. Both have very good seals but the FLC 8S is a better fit due to the very lightweight design.
The filter system on the T10 follows a very traditional path in terms of intended tuning with a treble, bass and reference tuning making a total of just 3 filters compared to the 36 possible combinations of the FLC 8s. On the flipside, they are super easy to work with and you will not lose the T10 filters as they work in the same manner as the I3 filters.
The biggest problem I had with the T10 was the core tuning. It was incredibly bass dominant that anything but the treble filter gave it a semblance of balance. If you are after a powerhouse bass response the T10 will give you an abundance of that with the bass and reference filters but it comes at a cost of drowning out everything else. The FLC 8s strongest bass filter is the red sealed ULF and black LF but even then it is still relatively coherent and enjoyable.
Using the balanced setup of the FLC 8s and the treble filter of the T10 I find the T10 to be a darker sounding experience and lacking in top end air compared to the more open sounding FLC 8. The low-end is powerful for sure on the T10, more so than the FLC 8s.
The mids lack a little in clarity and in the T10 and perhaps not quite as resolving and spacious sounding at the FLC 8s. Treble on the T10 is a little too rolled off in comparison and tends to push down a bit too much on the slightly dipped mids and competing bass weight. If you love a dark signature this is it but I think you will find yourself gravitating to the more open, cleaner and airier sound of the FLC 8s.
The T20 righted a few wrongs from the T10 setup and also introduced a new dual coil driver in the process. It retains the beautiful metal injection molding design so it more or less has the same fit and comfort levels as the T10. The FLC 8s in comparison will be lighter and maybe a bit more comfortable but not as robust in build quality.
The T20 is not the most efficient out there on paper at 16Ω at 90db but it actually is easier to drive than the T10 though not as efficient as the FLC 8s. higher noise floors will still be the Achilles heel of the FLC 8s in comparison but it will also take to weaker sources and smartphones much better than the T20.
The filter system is the exact same as the T10 with a reference, treble and bass set of three filters and is more basic in tonal tweaking than the massive array of options on the FLC 8s. And once again, it is a much easier system to chop and change. I can some preferring the higher tweakbility of the FLC 8s and others wanting the more guided simplicity of the RHA system.
Again the treble filter on the T20 is more reference sounding to me than the reference filter so we matched that up with the FLC 8s balanced filter combo.
The T20 is a more aggressive warm to slightly neutral tonality than the T10i. It also has a more prominent upper mid-range and treble performance. Everything is a touch more forward with plenty of sparkle and energy, especially around the 2-5k range. The bass still has a strong bias but this time it’s not a hugely colored experience like the T10i. I still rate the T20 as a musical IEM built for modern musical genres but this time everything just feels more controlled and tighter making it a far more flexible than the T10i.
Against the FLC 8s, it is much more competitive sounding than the T10 but that low end of the FLC 8s just has that bit more power and better sub-bass presence which tends to open things up a bit more in terms of staging depth.
Mids remain more impressive and resolving on the FLC 8s with better instrumental separation and positioning, better stage width. Vocal presence on the FLC 8 is slightly richer and more forward sounding.
Treble on the T20 is good and just as articulate sounding as the FLC 8s treble performance. If anything both are a little laid back sounding with the T20 perhaps delivering a slightly leaner sounding top end in terms of note body.
Cut away all the distractions with the filter system and the FLC 8s is actually a very impressive IEM for the money. It slays the RHA T series and is far more competent than the Icarus III from Trinity Audio, 3 other filter based IEMs.
It is just fluff if the basic tuning is not done correctly and in the case of the FLC 8s, you get a musical but clean and clear response that I personally find very engaging. Mix in the fact you can then tweak it to your heart’s content in oh so many ways and you really do have a ton of options right at your fingertips.
However, the bass and sub-bass filters are a nightmare to work with if you have big fingers and the tweezers are just a little too big for any sense of additional benefit. You will resort to your fingers tips. As sure as death and taxes you will lose a filter eventually and that is the weakness of the FLC 8s. The net outcome is sublime, but the process of getting there is akin to root canal surgery.
Having said all that this is the best sounding filter hybrid IEM I have heard to date at this price point. You can drag in the K3003 all you want but when it came out it was double the price. The FLC 8s is not quite there but its miles better than anything else at a similar price point using filters.
FLC 8S Technical Specifications
Driver unit: 8.6 mm dynamic drivers+ dual balanced armature