Fit, Build & Isolation
StealthSonics is no newcomer to building IEMs and the C9 Pro build is simply
superb, the shell is
flawless and the smoke transparent show great
craftsmanship on the internals. I picked simple colored transparent faceplates but the result is really nice and I love looking at them as much as I love to listen to them. The 2 pin socket is
recessed, which has my preference for a more secure fit.
As you can see there are 3 sound tubes and bores are flush, which means be careful with was obstructing bores. I admit I prefer horn bore designs (like the EM10 or VE8) for that reason but it’s not widely spread yet.
StealthSonics C9 Pro build is flawless and shows perfect craftsmanship, fit is superb as well. For those of you that are used to customs, note that the fit is on the
relaxed side
(special thanks to @Deezel177 for his input on this) so if like me you like your fit a bit tighter with lower tolerances then don’t hesitate to ask.
StealthSonics took my now usual
digital prints and the build time was
pretty fast around 2 weeks, the result was perfect from the get go the seal is great as well as comfort. This is top notch custom experience.
Introduction
The folks at StealhSonics are a
« group of audiologist, engineers and musicians that have been serving the audiology and audio needs of musicians, audio professionals, audiophiles and patients in SouthEast-Asia for almost 10 years ». I confess I hadn’t heard about them before I took part to the U2, U4, U9 review tour but I am glad I had the opportunity to discover the brand.
The C9 Pro is the upcoming flagship
(it’s actually not released yet) from StealthSonics along with the C9 with both a different tuning and technologies. The C9 was a hybrid with a dynamic and 8 BA while the C9 Pro is a 9 BA setup. StealthSonics does quite a bit of R&D and has its own techs implemented in the C9 Pro
“Klarity valve to reduce pressure build up and fatigue in the ear canal from long usage; Stealth damping for more controlled bass response ; and SonicFlo Acoustics for resonance and cancellation reduction.”
In the lineup I really liked the
U9 which is ruler flat reference and loved the more organic
U2 as it fits my personal preferences in terms of signature. Basically I liked the U9 technical chops but the signature of the U2 stuck with me. When I heard StealthSonics was coming up with a flagship with a very organic tuning my interest was piqued to say the least and I jumped into the opportunity of getting it early!
Sound
From the very first minute listening to the C9 Pro it was apparent that it was everything I hoped for and then some… the C9 Pro is the
epitome of an organic signature to me, which is a full bodied, richly textured, full of nuances and smoothly delivered sound. But it doesn’t stop there, as we’ll see and that’s what sets it apart.
The bass line is powerful with a clear mid bass focus, and the C9 Pro has a lot of slam factor. Mids are full bodied with beautiful textures and a smooth delivery yet very open and articulate. Treble is exquisitely tuned combining excellent lower treble sparkle and energy along with excellent upper treble extension providing air and resolution as well as balancing the overall signature. The C9 Pro is organic, but it’s neither dark nor congested quite the contrary. Soundstage is excellent and very coherent making for a very precise 3 dimensional image. The overall coherence is flawless, and reflects a masterful tuning.
Bass
The C9 Pro bass is
well extended and
controlled but with a clear
mid bass emphasis – the delivery is on the smoother side – with a
soft attack and a tad
longer decay. Bass notes linger a bit and decay beautifully.
It’s not a snappy, punchy bass but rather a more
romantic delivery with
beautiful textures and a high level of
detail and very good
control. Don’t mistake this for a weak or slow bass, the C9 Pro has a
powerful bass line and it can keep up with faster paced music it only does so with a smooth delivery at all times. This is a fairly singular presentation among all the IEMs I have listened to and I must say I like it especially on percussion where the C9 Pro conveys
nuances of interpretation in a way that not many IEMs can.
On José James
“Better Off Dead”, Nate Smith drums are exquisitely rendered and and Ben Williams bass line is powerful with a lot of weight to the notes. In Lucy Dixon
“Stormy Weather”, David Aknin drums also shine with the C9 Pro lots of nuances and interpretation cues. I also loved the way the C9 Pro presents the double bass on Jazz tracks, rich, soulful but some might find they prefer a snappier presentation. I like that the C9 Pro offers something different from most IEMs there and Caro Emerald
“Back it up” sounded just as good as I have heard it.
Out of more powerful sources, like iFi Audio ICAN Pro or iBasso DX220 Max, it’s very apparent that the C9 Pro will scale yet a bit further with a more powerful source providing even better control and more slam factor.
Mids
The mids are the heart and soul of the C9 Pro, it’s a
full bodied, richly textured and smooth mids with beautiful vocals.
The lower mids are probably among the very best I have heard elevated enough to provide satisfying body but not so much so that the mids would become congested. It’s also one very distinctive item of the C9 Pro’s tuning in a day and age where a common way to gain clarity is dipping lower mids. As we’ll see in the treble section, the C9 Pro relies on other qualities to bring clarity. This lower mids tuning highlights fundamentals on the rythm section of tracks and the C9 Pro has a
strong rhythmic emphasis which makes for great
toe tapping factor along with its mid bass emphasis. It also makes some older albums (80s come to mind) more enjoyable.
Coherence between the bass and mids is also a remarkable quality of the C9 Pro’s tuning, while there is no bass bleed into the mids the transition is seamless.
The upper mids on the other hand are on the smoother side, there is good
percussive attack and electric guitars have great
bite but above around 5kHz there is a dip and some might find hi hats to lack crispness, kick drums and toms to lack a bit of snap and brass instruments are on the safer side. On the flipside this makes the C9 Pro
non fatiguing and tracks like Hank Levy
“Whiplash” or Miles Davis
“So What” are absolutely devoid of any agressive hints that have me reach the limit with some IEMs.
Last but not least vocals on the C9 Pro are special, thanks to the fullness of the lower mids male vocals have
power (Leonard Cohen
“Nevermind” never sounded so good) and female vocals are on the
sweeter side but it’s not overdone. This makes for a romantic presentation so to speak. The presence range is elevated and there is
vocal emphasis, and the upper mids being on the safer side there is
no hint of sibilance whatsoever. As we’ll see to bonify things the upper treble brings welcome air to an otherwise
sweet and romantic presentation, making the C9 Pro a superb vocal performer in my opinion as it also emphasize higher notes and James Blake
“Vincent”, Etta James
“At last”, Ruth B.
“Lost Boy” are some of my vocal test tracks I enjoyed a lot with the C9 Pro.
Treble
The C9 Pro treble, as I hinted earlier are key to its signature. The power of its mid bass and its full bodied mids is balanced by the energy of its lower treble and its superb extension and presence. Consistently with the rest of the signature, the C9 Pro delivers its treble section with a
smoothness that is so very elegant to my ears.
The lower treble features excellent
sparkle and piano notes have great
energy and
weight, the Hot Sardines
“Comes love (l’amour s’en fout)” intro is simply superb. In a very different genre Infected Mushroom
“Jeenge”, Erez Aizen acoustic guitar is superb as well as the airy synth sounds. Also worth mentioning, Stan Getz
“Maracatu-Too” where Jose Paulo and Luiz Parga percussions are simply beautiful.
Uncharacteristic for a very organic IEM, the upper treble has
excellent extension and
presence, which brings a lot of
air and
refinement to the C9 Pro signature but also grants the C9 Pro
impressive resolution and
detail retrieval as well as
excellent separation. This is even more apparent out of DX220 Max versus the smoother LPGT where the C9 Pro reaches impressive resolution. The upper treble presentation reminds me a lot of Vision Ears VE8 and that’s not a small compliment. It’s a very effortless and consistent across the range – again – smooth presentation making for a very natural presentation, refraining from any artificial accentuation which is the sign of a masterful tuning.
Verdict
The C9 Pro is without a doubt my favorite IEM from StealthSonics and has quickly earned a place as one of the top favorites in my collection along with Custom Art FIBAE7 and Earsonics EM10. It’s a daring choice in this day and age for a flagship to go for a more organic signature but StealthSonics has delivered with the C9 Pro a flagship that is both technically impressive and a masterful organic tuning with its own unique twist.
If you’re looking for an IEM that is highly engaging and smooth with a strong bassline, full mids with superb vocals and very refined and elegant treble then the C9 Pro is definitely among the top options especially at its price point! If you like your organic signatures with a bit snappier and punchier bass presentation, clearer mids with more bite and energetic treble then there are other alternatives as we’ll see in the comparison section.
Note that for those of you who prefer universals the U9 Pro will also be available.
Listening notes
I spent approximately 300 hours with the C9 Pro , listening on Lotoo PAW Gold Touch, DX220 Max and PAW S1 using PW Audio n°10, DITA Oslo and Dunu Blanche balanced cables.
Special Thanks
Thanks to Raj at StealthSonics for providing an early preview to the C9 Pro at a discounted price.
As usual, this review is my honest opinion. No incentive was given for a favorable review.
Due to character limitation I can't post the select comparisons with FIBAE7, EM10 and U9 here but you can find them on iem.reviews and on the C9 Pro thread.
