Review: Stealth Sonics U9 JDM | Methods and Melodies

Tantalizing works of art, plus random splotches of paint in the background.
Tantalizing works of art, plus random splotches of paint in the background.

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Although a Japan-only release, something this good should not be hidden for long. Marvel at the 9-driver co-flagship hybrid made by Stealth Sonics, a Singaporean company with a rich background in audiology.

The human ear is a fascinating organ. Encompassing less than 1% of our body mass, this weird-shaped piece of flesh is a hotbed of diseases to doctors, exotic cuisine to Mike Tyson, and totally reviled by Picasso. To the rest of us, it conducts sound, beautiful sound, from the most soothing lullaby to your wife’s deafening orders. Indispensable.

Stealth Sonics would probably know more about the ears than most of us. Founded by a team of audiologists, engineers and musicians, this Singaporean outfit has deep, deep roots in audiology and hearing aids, serving musicians, audio professionals, audiophiles and patients in Southeast Asia for a decade before branching out to in-ear monitors (IEMs) as their next field to conquer.
Bottom Line

The U9 JDM, besides boasting ridiculously good sound quality, provides excellent value for money for what you’re getting. If the economy is the language of love, Stealth Sonics would be whispering "embrace me, my love" gently to your ear.

What We Like 😍
  • Complete accessory set
  • Unique, functional design
  • Excellent comfort
  • Good stock cable quality
  • Highly detailed and energetic signature
  • Visceral, clean bass
  • Accurate tone and timbre
  • Elite vocal performance
  • Airy and transparent treble
  • Value for money
What We Don't Like 🤢
  • Short nozzles hinder fit
  • Average sound isolation
  • Shells might be too big for small ears
  • Bass layering
  • Treble is sometimes brittle

Science, Baby!

And how does one conquer the world? With science!

Years of experience in all things audio means a rich vein of research and development is tapped to forge the best IEMs in the market, from the audiologists’ point of view. So not only do Stealth Sonics’ IEMs have sound quality in mind, but also the technology and innovation to make listening as comfortable and safe as possible.

Today we look at their flagship, with a twist. This is the U9 JDM (Japanese Domestic Market), sold exclusively in Japan with a different tuning from their original flagship, the U9. The JDM is their hybrid creation comprising 8 balanced armatures and a dynamic driver, coalesced with a 4-way crossover and 3 sound bores.

Tantalizing works of art, plus random splotches of paint in the background.
Tantalizing works of art, plus random splotches of paint in the background.

Exotic Quixotic

The U9 JDM shares the same driver configuration as the U9 but was tuned in collaboration with a renowned Japanese sound engineer, the end result being an emphasis on vocal performance. They retail for $1099 (or ¥121,880) but are not available officially. You’ll have to drop them an e-mail for purchase details. The custom version (dubbed the C9) can be ordered too.

I would like to thank Mr Rajeshpal, general manager of Stealth Sonics for the loaner review unit, and for allowing me the opportunity to listen to this rare gem. Saved me a trip to Japan!

Equipment Used:


  1. Sony NW-WM1A “K” Modded, FW 2.0


  1. Stealth Sonics U9 JDM
  2. Empire Ears Legend X
  3. Vision Ears VE8


  1. Amber Rubarth – Scribbled Folk Symphonies
  2. Daft Punk – Random Access Memories
  3. Diana Krall – Quiet Nights
  4. Fleetwood Mac – Rumours
  5. George Michael – Ladies and Gentlemen
  6. Lana Del Rey – Honeymoon
  7. Robert Plant & Alison Krauss – Raising Sand
  8. Susie Aroili – Night Lights
  9. Travis – Singles
  10. The Eagles – Hell Freezes Over

Technical Specifications

  • Drivers: 9
  • Type of Drivers: Hybrid
  • Configuration: 1x Dynamic Driver (low), 2x Balanced Armature (mid), 2x Balanced Armature (high), 4x Balanced Armature (super high)
  • Crossover: 4-Way
  • Isolation: -26dB
  • Bore: 3
  • Frequency Response: 18Hz – 40kHz
  • Sensitivity: 108dB SOK @ 1mW
  • Impedance: 16Ω @ 1kHz
  • THD: <=1% @ 1kHz
  • Warranty Period: 1 year
The ragtag cast of the Flat and the Funky part 8.
The ragtag cast of the Flat and the Funky part 8.

Packaging and Accessories

The U9 JDM packaging is a treasure trove of thoughtful accessories. It’s like opening a box of Turkish delights full of color and variety, or maybe I’m just hungry. A tall, dark and handsome box lined with a carbon fiber motif welcomes you at unboxing. Inside you’ll find more than enough accessories to customize your listening experience.

  • 7 pairs of ear tips (3 pairs foam in S, M and L sizes, 3 pairs silicon in S, M and L sizes, 1 pair silicon double-flange)
  • Stealth Pro 3.5mm cable (silver-plated copper stock cable)
  • Stealth Mic 3.5mm cable (with microphone and in-line controls)
  • Airline adapter
  • ¼ inch adapter
  • Extra faceplates with hex key
  • Zippered case
  • Drawstring pouch
  • Microfiber cleaning cloth

The accessories are well-made and not just slapped together for the sake of completeness. The case is robust and roomy, while the cables are of very high quality. Consisting of 4 braids of silver-plated copper, the Pro and Mic cables are lightweight, and handle very well with superb ergonomics. Unless you choose the upgrade path (and I’m sure you will), these do a good job temporarily.

Planking's great exercise, that's why they weigh so little.
Planking’s great exercise, that’s why they weigh so little.

Design and Build Quality

IEMs are a great way for designers to express their creativity. Look at the ravishing, esoteric designs done by Acoustune and Astell&Kern, anything goes as long as it ends in a nozzle that can be jammed into the ear. The Stealth Sonics U9 JDM has a distinctive look that is instantly recognizable, resembling a mini solar system resting on a vast space of carbon fiber.

But more than the unique exterior, there is a method to this madness in design.

The U9 JDM earpieces carry a host of in-house technologies backed by their research. They’re not just for looks.

  • Iso-Stealth: The shape and size of the universal shells are based on a large data bank of ear impressions, optimizing seal and isolation.
  • Stealth Kompozit: A soft, matte-like nanocoat finish on the shells for maximum comfort.
  • SonicFLO Acoustics: The use of asymmetrical sound tubes to preserve higher frequencies and harmonics.
  • Klarity Valve: A valve to release pressure build-up in the ears to reduce listening fatigue and hearing stress.
  • Stealth Damping: Damping technology at the faceplate for more extended bass response.
  • Ultra Hard Impact Shell: Exclusive to their custom IEMs, a proprietary lacquer coating that increases shell toughness and provides some drop protection.

Hard Core

The entire U-series deploys the same design, while the trim color differentiates between models. The lower-end models might have playful colors, but the U9 JDM, like Jay-Z’s style preference, is all black everything, even the extra faceplate.

As for build quality, the U9 JDM looks meticulously assembled. From the faceplate to the smooth shell and thick nozzle, they are well put together, and should last a few years if you take good care of them. I’m curious how the matte finish of the shells will end up with years of use, since matte finishes tend to be harder to maintain.

These seashells look kinda weird and screwy.
These seashells look kinda weird and screwy.

Fit, Isolation, and Comfort

If you’ve ever held a teddy bear to your face in a department store when no one’s looking, you’re my people, and appreciate the finer things in life. The U9 JDM’s smooth, lightweight shells begged to be worn, but finding the best fit was daunting at first. Due to the short and thick nozzles, the fit was shallow without a complete seal in my ears, even after trying most of the stock ear tips.

Hello Teddy

Only after some vigorous tip-rolling did the U9 JDM magically come to life. SpinFits work, but my favorite ear tips were Final Audio’s Type E, which gave me a deep insertion and full seal, giving arguably the best bass response and realizing the IEM’s full potential. With an optimum fit, sweet, sweet comfort fell into place, like burying my head in a pool of teddy bears.

The best part is I could wear the U9 JDM for hours because they felt nearly weightless. Despite the high driver count, you’d never guess they’d be this light. Surely Stealth Sonics weaved some magic into this. Isolation is average however, due to the vented shells. They won’t completely block outside noise, so that’s something you have to consider if you want to commute with them.

My planet, my planet for your granite!
My planet, my planet for your granite!

Sound Quality

Design quirks, rich audiology pedigree and unicorn-like exclusivity notwithstanding, we arrive at where it matters most, the sound section of the U9 JDM. Come one, come all.

Overall Sound Signature

Stealth Sonics’ U9 JDM is an alternate tuning to their co-flagship, the U9. The JDM has what enthusiasts call a “Japanese tuning”, that is broadly speaking, a middle mids to upper mids boost for emphasis in female vocals, because a heavy proportion of Japanese and anime music has exactly that. Weeb and otaku stuff.

The Japanese tuning monicker though is not meant to scare anyone off, rather a signal for vocal lovers to look their way. The U9 JDM can still be enjoyed even without any Japanese music, like my playlists, which are mostly a collection of scruffy, bearded, black-clad men yelling over their guitars. Others call it rock.

The U9 JDM has a neutral-warm tuning, with a sub-bass and upper mids emphasis. It is fun and lively from the get-go, but bearing the co-flagship tag means doohickeys like resolution, layering, and timbre cannot be ignored. Rest assured they perform very well here, but the main course is in the vocal tuning, which is exceptional, to say the least.

Listening Conditions

Critical listening was done after 100 hours of burn-in. I can attest that the U9 JDM’s bass tightened up a bit, and transients are more easily heard. Good, but not a night-and-day difference. The main review rig is Sony’s NW-WM1A Walkman modded by Project K, using the stock cable, and Final Audio’s Type E ear tips.

From some angles the U9 JDM looks like a very agreeable mustache.
From some angles the U9 JDM looks like a very agreeable mustache.


Christmas. Thanksgiving. The Gilroy Garlic Festival. Every occasion to celebrate should be bookmarked by episodes of indulgent, decadent overeating. Even in music, the bass should be the cornerstone of every nutritious musical meal, and like holding a pair of aces, the U9 JDM has them in spades.

Full Course

Reaching downwards to the nether regions, the sub-bass is hearty and wholesome, and a full course in itself. The thump and rumble are clearly felt and forces a lump in your throat. This bass is serious business, with glorious extension and authority. Going to the midbass, the quantity is less so than the majestic sub-bass, but is punchy and dynamic enough to deliver a full-fisted, well, punch.

The midbass tails off approaching the upper bass, lending a clean break with no bleed into the mids, so your bass is not only bombastic, but wonderfully measured and disciplined. Note texture is well-rounded with precise, hard-hitting attacks and a natural, smooth decay. On occasion, notes are too full and layering suffers, but overall the U9 JDM bass prepares you for a rip-roaring, shirt-tearing good time.

First deflower, then devour. Can you be-leaf it?
First deflower, then devour. Can you be-leaf it?


Like watching Will Smith suddenly become a fantastic dramatic actor in the Fresh Prince, the mids are the U9 JDM’s star turn. Masterfully tuned with the hands of a musical maestro, we witness an astute balancing act of transparency and musicality unfold in our ears. It is tuneful, natural and utterly engrossing.

Tears on my Pillow

From the lower to upper mids, notes have a velvety texture, with alluring intimacy and effortlessness to the sound. Note body is just enough, fully-formed and spacious without overbearing the signature. Speed and layering take a mindful step back, but the U9 JDM’s greatest strength is in the timbre and tonal accuracy.

In turns smooth and gentle, at other times ferocious and fearless, they never lose sight of the ultimate aim of the mids, that is to convey voices, instruments, and emotions as naturally as possible.

The mids swell and flow with emotion and heart. The vocal tuning, especially, takes center stage, sounding realistic and enchanting, male or female. From Buble to Sade, the delicate vocal renderings made me want to close my eyes and fade into their voices. Soothe and lull me to sleep with your delicate vocal cord trembles, my sweet. You haven’t heard vocals until you hear what the U9 JDM can do.

It's that time of the year to put tiny things inside huge boxes and pretend we care.
It’s that time of the year to put tiny things inside huge boxes and pretend we care.


Like the joker in the pack, this is a playful one. Free from the clutches of the full-bodied bass and leading-role mids, the treble grows a pair (of wings) and takes flight. The treble, especially the lower part, has notes that are light, feathery, and fluttery, dancing and floating away in a sky full of dreams and possibilities.

Like a Bird

And after a trip to the celestial kingdom, the treble brings back souvenirs, lifting the entire sound spectrum with air, wondrous air. The spaces between the notes and within the notes are pleasantly present, resulting in an airy treble that shines, sparkles and shimmers with lively exuberance.

The U9 JDM treble excels musically and technically, sounding both detailed and well-layered while staying clear of sibilance. The only complaint I have is that the treble can be too airy and lacking body, sometimes sounding brittle and overtly-crispy. Other than that, it’s a one-way ticket to one of the most irresistible trebles I’ve heard.

“Look Simba, everything the light touches is our kingdom.”

Soundstage and Imaging

The soundstage is the vessel that carries the minute musical mayhem of the sound signature, and also the stage manager that makes sure every element in the music has an equal spot in the limelight. The U9 JDM has a stage that is sufficiently wide and deep, affording space for the ample bass bloom, vocal theatrics, and hummingbird-like treble.

There are bigger stages out there for sure, but the U9 JDM leaves little to be desired, with no details overlooked nor spared here. Imaging and separation are worthy as well, with well-defined layers from front to back, and left to right, with very little smearing and almost no congestion. The soundstage height is quite short though, hampering imaging a tad, and prevents it from being among the elite.


Empire Ears Legend X

At more than twice the price, surely the U9 JDM is biting off more than it can chew? Not so fast, this is a much closer battle than you think. My basshead endgame, the Legend X renders bass like no other, sounding epic, magnanimous, and just brimming with authority, while maintaining a pleasing signature throughout.

There is no doubt the U9 JDM has gentler bass, and sounds much flatter with less slam, impact and satisfaction levels, but in doing so unlocks rewards in the other parts of the spectrum. Legend X’s bloated and forward bass obscures the stage and makes the U9 JDM sound cleaner and clearer in comparison. Switching to the Stealth Sonics is like breathing fresh, pristine air.

The bassy, ballsy, boisterous, bombastic brothers.
The bassy, ballsy, boisterous, bombastic brothers.

Out of Reach

And at the expense of the bass, U9 JDM’s more present and euphonic mids proves more pleasurable than the Legend X, especially in the upper mids where Legend X seems too reserved and muted. From the mids up, Legend X is smoother but more recessed, taking less risks the higher we go. It’s a similar story with the treble, where Legend X rolls off early, while U9 JDM shines and sparkles although sounding a bit brittle.

The Legend X dwarves the U9 JDM in soundstage, besting it in all 3 dimensions, but U9 JDM has more accurate imaging because Legend X’s bass tends to overwhelm the signature.

In short, I’m as surprised as you how well the U9 JDM keeps up with one of the most vaunted hybrids in the market.

Vision Ears VE8

You can’t mention good mids without the mighty VE8 glancing over. Bestowed “best tuning ever” in my other review, the VE8 is a flagship-grade IEM that takes on all comers and oftentimes emerges the winner with nary a scratch.

U9 JDM takes an early lead, displaying a more natural-sounding bass with better low-end extension and a more pronounced sub-bass thump. VE8, however, has a meatier midbass and speedier decay, leading to a tidier stage with better layering ability. In the treble, VE8 shows more finesse and better note body, free of the brittleness of U9 JDM but with all the sparkle and sizzle.

The Epicenter

The main confrontation is in the mids. Both share a lifelike timbre and tonal accuracy. Vocals are equally pleasing, with VE8 more filled-out in male vocals while U9 JDM has more ethereal female voices. The main difference is in note presentation. VE8 is lusher and bolder, with dramatic flair and power, like painting with broad strokes of a brush. U9 JDM is airier, thinner and more precise, like fine needlework.

VE8 pulls ahead of the U9 JDM in soundstage and imaging, possessing a larger stage while exhibiting more precise layering and separation. The VE8 might be victorious, but both are simply amazing IEMs to listen to because of the mids tuning. This is a testament to the inherent value of the U9 JDM, to be able to compete toe-to-toe with the VE8 which is considered one of the best IEMs ever made.

After a pummelling by the U9 JDM, you do get a nice view.
After a pummelling by the U9 JDM, you do get a nice view.

Final Words

Look at you, the tired and broke portable audiophile, lamenting at escalating prices and relentless choice. It wasn’t too long ago when top-of-the-line IEMs can be bought for a thousand bucks, but today the ceiling is raised to 4 times that. Surely the path to sonic enlightenment has to be easier than this. I’ve been there, amigo, and the financial drain dents your wallet and wellbeing with no end in sight.

Love and Economy

Stealth Sonics is one company that says you don’t have to spend top dollar for flagship-level sound. The U9 JDM, besides boasting ridiculously good sound quality, provides excellent value for money for what you’re getting. If the economy is the language of love, Stealth Sonics would be whispering “embrace me, my love” gently to your ear.

In case you missed it, I love the U9 JDM, and hope it can be released to a wider audience someday. From the concept stage, to the hard work by the audiologists and engineers, and finally to you, every step of the way has been a labor of love by Stealth Sonics to provide maximum enjoyment while keeping a close check at your hearing. This is a top-level hybrid you can proudly show off to your friends.

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