Things that I would definitely change as the Manufacturer:
Different cable (the jacket will fray over time).
Threaded 2.5 mm TRRS to 3.5 mm TRS adapter (the 2.5 mm connection isn't known to be sturdy).
Larger included tips (the silicone tips aren't the largest) and/or longer nozzless and/or more rounded faceplate design edges.
Sound:
Mainly low impedance sources are what I use for the Fidue.
For listening below, I always use the largest size of the included silicone tips.
Tonality:
I surely had no idea how the SIRIUS was tuned, but a few presumed sound signature characteristics I had in mind were a smooth, musical and slightly warmed-up bottom end with a sparkling yet not overdone treble, an even and coherent sound along with some musicality and fun without neglecting class and maturity.
And it turned out that I was not too much off with my assumption although it turned out much more balanced than I expected – what I am hearing is a very moderate elevation in the bass that is however so far from being overdone and just slightly north of neutral, relatively balanced, and reaches quite deep but loses a little quantity in the lowest registers of the sub-bass (editor's note: depending on how much the dynamic driver's front cavity vent is blocked, you might however get a leaner or beefier presentation that what I am hearing; this is an advantage if an in-ear has got the front cavity vent located in an area where it may or may not be blocked as a result of one's individual ear anatomy, and it's an "issue" most in-ear that utilise dynamic drivers in vented shells have). So there is enough sub-bass and it is there when called upon, but it is not the extroverted star of the show and takes a small step back compared to the upper bass and midbass. Upper bass has got a nice punch to it, with some slight smoothness and warmth in the lower root that however ebbs away quite soon so there is no spillage into the lower mids and no unnecessary added warmth in the rest of the root – just enough to make the low end appear musical yet not too smooth or warm.
The mids’ timbre is pretty good to my ears, with vocals sounding quite realistic and mostly uncoloured. Because of a moderate emphasis in the lower treble, mids’ overtones have a slight upwards shift without tending to the coloured side in my ears though – the lift just adds a little more air without making the timbre shift to the unnatural side. Speaking about timbre, pianos and trumpets or saxophones don’t really sound altered but quite natural to me, as opposed to the UPQ Q-music QE80 (OEM of the Fidue A83) that shifts trumpets a little to the thinner side, or my circumaural Audio Technica ATH-MSR7 where vocals’ overtones are on the slightly brighter side as well but where trumpets sound more like a squeaking noise than actual instruments.
The treble is ultimately somewhat more on the brighter side, with an even rising lift from the lower to upper treble. I would not be surprised if there is some sort of countervailing dip in-between, as there is no edginess or unevenness and the treble is not obtrusive although it is somewhat emphasised, but I’ll find that out quite short when I do my usual sine sweeps. Air and extension past 10 kHz seem to be quite good and there is some nice subtle sparkle in the super treble past 10 kHz.
What kind of amazes me similarly to the Q-music QE80 is that although the upper end is on the brighter side of neutral, it lacks sharpness or edginess and sounds coherent as well as easily tolerable. It is not yet as harmonious as my Etymotic ER-4S’s treble which is probably the most even treble I have come across, however among the in-ears with a brighter upper end tuning, the Fidue definitely belongs to those with a very coherent and annoying-free character.
So overall, I would say the SIRIUS falls into the category of a balanced w-shaped in-ear that is overall natural sounding and slightly leans more towards the brighter side without being annoying at all.
Bass quantity by the way depends on how much the small vent is covered up by one’s ears. In my ears, it is not covered all that much, so it gives just the necessary amount of boost in the low-end so that the sound does not become boring but has a nice texture and musicality to it. Depending on your ear anatomy, the bass can be either more present or a little leaner. If you are into modding, you can of course also perform a tape mod to close the small vent in order to achieve more low-end quantity and impact.
Further below when I perform the sine sweeps, listen to noise and determine by how much certain frequency bands are boosted and by how much, I will be able to tell the bass quantity the SIRIUS has in my ears. My guess would be around 4 to 5 dB compared to a very flat in-ear like myER-4S and probably 2 dB more compared to my UERM.
So overall, one can definitely recognise some of Fidue’s hybrid in-ears’ house sound in the SIRIUS which has however matured, having less bass quantity than the A73 and UPQ QE80 in my ears, with less warmth in the lows, less root warmth and better extension towards the lowest sub-bass. Overall, it seems like the A83/QE80 was taken as a base for the SIRIUS which was however tuned for a more balanced and mature, less gimmicky "fun" tonality, with a more realistic timbre in the lower treble and less sibilance although I already didn’t have much to complain about the QE80 in this regard.
So yeah, it is quite a flagship-worthy tonality with an excellent balance between maturity, musicality and moderate fun.
Moving on to what I hear with the sine sweeps, noise and EQ counter-checking: from about 450 Hz down, the lows’ emphasis starts climbing, reaching the climax with being ca. 5 dB north of neutral compared to a completely flat in-ear (Etymotic ER4S/SR) at about 200 Hz, which is kept upright down to 35 Hz from where on it rolls somewhat off towards 20 Hz. This gives the sound some non-overdone impact and enough bottom end and lower root warmth to not sound sterile.
From 1.3 kHz on, level starts increasing up to 7.6 kHz where the treble emphasis’s climax is located. From there on, it takes a slight step back without becoming dark at all and reaches very high past 17 kHz.
Resolution:
What I got was mostly what I expected – hybrid flagship-like performance.
The bottom end is excellently controlled and quite quick and nimble. And it is not any soft at all although typical for the dynamic driver, attack and decay are not as quick as with most BA driver implementations (on a second note though, it beats some back-vented BA in-ears in terms of bass tightness, sounding less soft and better controlled). Contrary to what I expected, the attack has about the same speed as the decay and lacks a very slight bit behind the FLC8s’ dynamic driver’s speed, but what the SIRIUS still has got is some addictive yet not overwhelming bass body and tactility, which is the main reason why many people love a dynamic driver for the lows. And oh yes, the SIRIUS does such a great job down there, finding just the right balance between speed, body and control. It just handles fast Metal as well as Electronic music with great control as well as ease and has still got that dynamic driver’s body. On another note, I wouldn’t be much surprised if one of the five acoustic ways also contains a BA driver for the lows in addition to the dynamic drivers, as the bottom end is pretty clean and fast while still having that really nice body.
Moving to the mids, they are nicely textured and detailed, revealing small variances of the singers or multiple layers with an easy-going and smooth, highly detailed character. Because of the upwards slope in the treble, there is a little more of a favour of female vocals because of the more up-front overtones, but male vocals are no less detailed and and layered just as wess.
Treble is excellent as well and although it is a little more on the bright side, it becomes never annoying and single notes are cleanly as well as precisely separated from each other.
Overall sound is highly dynamic and realistic, with really good fine detail retrieval.
And of course, everything sounds very coherent. I know there is still more possible resolution when going up in price and I own and have a few technically somewhat "better" in-ears, but one usually has to spend over $1000, close to 2000, to get a comparatively small sound quality increment when put in relation to the price (keep in mind that the higher we go in price, the more the law of diminishing returns kicks in).
Soundstage:
The imaginary soundstage is indeed large, spacious, open and well-rounded. It is not as large as for example the (discontinued) UE18 Pro’s and not excessively wide, but very well rendered and rounded with precise instrument placement as well as really good separation, so the imaginary room is very tidy without instruments bleeding into each other what enforces the impression of a really nice and large appearing soundstage.
Overall, sounds are well detached and appear more to be all around the head - an open presentation.
Picking out the position of single notes, instruments or singers works pretty well and the soundstage has got a good forward-projection and sounds overall pretty realistic and – what I find most important – authentic, what so many in-ears in a lower price range do not achieve to the same extent. There is indeed some really nice air around instruments and notes.
Mission accomplished, the SIRIUS fulfills my expectations regarding sound.
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In Comparison with other In-Ears:
UPQ Q-music QE80 (OEM Version of the Fidue A83):
As mentioned above, the SIRIUS seems like the more mature and grown-up version of the QE80.
The UPQ has got more bass quantity which is also warmer and shines a bit more into the root, giving a fuller and warmer low-end response. The QE80’s upper mids are somewhat more on the brighter side, along with the lower treble, making trumpets and pianos sound a bit brighter than they are – here, the SIRIUS appears more realistic. Moving on in the treble, the SIRIUS is somewhat less bright despite the QE80 having a narrow dip in the middle highs (which is mainly only really noticeable with sine sweeps though).
When it is about detail retrieval, the SIRIUS is definitely an upgrade (in all areas): while the QE80 has got the more present body, it comes at the cost of speed and control with fast music, so the SIRIUS has got the better controlled and quicker bottom end. The SIRIUS’ mids are also better layered and textured, with the higher minute detail retrieval. In the treble, there is no major difference but the SIRIUS also appears slightly better separated despite being less bright.
The SIRIUS’ soundstage is somewhat wider while both have almost identical depth (going back and forth, the SIRIUS has a little more depth though). The SIRIUS’ soundstage is however better layered, textured and separated, with more precision and air between instruments, wherefore it sounds more authentic.
So yes, the SIRIUS is an upgrade to the QE80/A83 on the technical side and also more balanced sounding. Nonetheless, I still like the QE80 for its fun tuning.
FLC Technology FLC8s (red – grey – gunmetal Filters):
The SIRIUS has got somewhat less bass quantity but a bit more warmth in the root. In the mids, both are quite comparable although the FLC8s is a little more forward here. In the treble, the SIRIUS is the somewhat brighter in-ear, especially in the middle treble where the FLC8s has got a dip.
The FLC8s’ bass has got the somewhat quicker attack while both have similar decay, control and precision in the lows. The SIRIUS on the other hand has got the more tactile/visceral body.
The FLC8s’ mids are more detailed, even more than my UERMs’, so here it even outperforms the SIRIUS by a little.
In the treble however, the SIRIUS sounds more realistic around 10 kHz and reveals more details, seems a bit more easy-going overall.
The SIRIUS’ soundstage is somewhat wider and deeper but not by much. The Fidue’s stage appears a little better placed and authentic as well, while both have very comparable and precise separation.
Overall, both are quite close when directly compared. Here and there however, the SIRIUS is somewhat better albeit the FLC has got the more detailed mids.
DUNU DN-2002:
The DN-2002 has got the more forward bass in my ears but somewhat less sub-bass extension, however especially more root and upper bass quantity. The DUNU’s (especially lower) mids are somewhat more on the warmer and thicker side.
Both in-ears have got pretty comparable bass quality, and even the body is very comparable although the DUNU’s is more forward because of its higher bass quantity. In terms of control, the Fidue has a slight edge over the DUNU.
Moving on to the midrange, the Fidue’s appears slightly more detailed. It is a rather close decision though.
In the treble, the SIRIUS is somewhat more easy-going and has got the more refined upper treble – again, it is a more or less close decision.
Going on to the soundstage, both in-ears have got comparable size but the SIRIUS generates some more air between instruments and therefore has the even somewhat more precise imaging.
Ultimate Ears Reference Monitors:
My UERM, while not as flat as my Etymotic ER-4S when doing sine sweeps and listening to noise signals (as well as music), is still an overall very neutral in-ear.
Comparing the two, the SIRIUS has got somewhat more bottom end but really just a little. In the mids, both are comparable however in the upper midrange/lower treble, the Fidue has got the somewhat brighter overtones while both don't differ all that much in terms of midrange timbre in my ears.
In the middle treble, the UERM has got somewhat less quantity. Moving to the upper treble below 10 kHz, the Fidue is a little brighter, but around 10 kHz, the UERM has got more quantity because this is where it has got a peak.
With its BA driver, the UE has got the somewhat quicker bass attack and decay and little better control, however it is surprising that the Fidue comes really close but has that typical dynamic driver body (nonetheless with excellent control and quality).
In the mids, both have got quite comparable details with the UERM being ultimately ahead.
In the treble, the UE is a bit more detailed and better with craving out minute details and rendering them well. In the upper treble around 10 kHz, the SIRIUS is however a bit more authentic as well as realistically sounding (the upper treble has always been something where I felt my UERM could be a little more realistic).
In terms of soundstage, the UERM scales a little better depending on the recording and has got more width as well as a bit more depth. Both create comparable air between instruments but the UE’s soundstage appears a little better controlled with fast recordings (probably because of the different woofers).
Overall, the UERM is still the somewhat more authentic in-ear, but the SIRIUS comes pretty close in most categories and has got the even somewhat more realistic appearing upper treble around 10 kHz to my ears.
Shure SE846 (white Treble Filters):
My Shure has got more sub-bass and a sub-bass emphasis. The SIRIUS has also got slightly less midbass and upper bass quantity and is therefore a little tamer in the lows and more balanced sounding (but then again, as written somewhere above, bass quantity will depend on how close the vents are to one’s ears and how much they are covered). The Shure’s mids are somewhat more forward and a wee bit dark sounding to my ears. The SIRIUS has got the more even treble and especially better extension – above 8 kHz, the Shure is quite rapidly rolling off what causes cymbal crashes to sound somewhat cut-off.
In the bass and mids, both are really well comparable when it is about resolution. With its dynamic driver, the Fidue has got more bass body presence whereas the SE846 has got the very slightly better attack and control. Moving on to the treble however, the SIRIUS does not only sound more realistic (despite sounding brighter) and has got the superior extension, but is also more detailed where the SE846 sounds a bit blunt in comparison.
In terms of soundstage, the Shure’s is a bit more on the smaller side compared to other $1k in-ears and CIEMs, but not really any less precise, authentic or three-dimensional. While the SIRIUS’ soundstage is somewhat wider and deeper than the Shure’s, both have got pretty much identical authenticity, separation as well as air between instruments and appear similarly holographic.
If it wasn’t for the Shure’s slightly below-average treble, both in-ears would have been more similar than different (despite the different sound signature approach) on the technical side, but because of the upper end, I would ultimately give a slight edge to the SIRIUS when directly comparing both.
Conclusion:
The Fidue A91 SIRIUS has got a well-done tuning, is strong on the technical side and features a nicely open sounding soundstage, but some things about the shells, cable and accessories could be redesigned.