Thoughts On The Ocharaku Flat-4 SUI

I had been aware of the Ocharaku Flat-4 SUI for some time and had researched their sound signature thoroughly enough to believe there would be no surprises when I heard them — I was wrong.

Exterior, Packaging, Accessories, and Aesthetics

The packaging and SUI form factor are probably some of the strangest I’ve encountered. The IEM comes packaged in a circular tin tea case, and inside, we have the SUI, a pair of size L Comply tips with the M size already mounted on the IEMs, along with some company literature and nothing else. No extra tips to experiment with, no carrying case, no shirt clip — nothing.

The SUI housing is a dark durable plastic with a silver coloured tube running along the top of each housing, termed a ‘phase correction’ tube. Also, on the side of the housing is a small pinhole. This pinhole is used for venting purposes, aiding in increased sound stage. Running out of the housings is a rather unassuming, dark, cheap-looking cable with no strain reliefs on either end and no neck slider.

My first thought upon handling the SUI was ‘care’, as in, handle with care at all times, due to the lack of cable strain relief. Inside, the SUI has two 10 mm dynamic drivers, called ‘elements’ by Ocharaku, and mounted, interestingly enough, parallel to one another.

The Flat-4 SUI.
The Flat-4 SUI.

Design Aspects of the Flat-4

The shape of the housing, the phase correction tube, the way the drivers were mounted, and the pinholes are all key in how the SUI is tuned. According to Ocharaku, the SUI is intentionally engineered this way to meet four key points in tuning (quoted directly from the Ocharaku site):

1st Effect: Placement of opposed elements reduces mechanical vibration due to anti-resonance.
2nd Effect: Twin element parallel drive improves sound pressure sensitivity of low to middle frequency sound.
3rd Effect: External auditory meatus tuning technology using phase correction tubes dramatically improves middle frequency sound.
4th Effect: Deletion of acoustic resistance and employment of small elements dynamically enhances ultra-high frequency sound and realizes wide sound propagation.

Needless to say, the SUI takes a very interesting and creative approach, engineering-wise — how Ocharaku has chosen to solve the various problems associated with properly tuning an IEM is certainly unique.

The SUI imparts a V-shaped signature — a very mild V shape, so much so that I really don’t like to use the term “V-shaped” to describe this IEM’s sound signature. Although the treble and bass are accentuated, They’re quite tastefully done.

The Flat-4 SUI with Westone STAR tips.
The Flat-4 SUI with Westone STAR tips.

The sound stage, to me, is this IEM’s greatest strength. It very much provides an out of your head experience, able to mimic the immersive feeling a listener experiences with a full-sized headphone. Spatial cues seem to materialize out of nowhere around the listener’s head and are clear and precise in their positioning. Because of the rather large sound stage, width, height, and depth, there is no lack of air between instruments and busy musical pieces don’t sound cluttered, but rather wonderfully expansive. In my opinion, Ocharaku makes some of the better earphones on the market that successfully replicate an involving, immersive sound stage.

The SUI bass is very linear, detailed, and precise. It extends low, and although I wouldn’t class it as full-bodied and thick sounding, unlike other earphones on the market, it can still punch and slam acceptably well. It’s tuned in such a way that the bass threads a very fine line — somewhere between lush and thin. Although bass notes can sound borderline thin and decay rather quickly, somehow, the SUI seems to retain enough body to keep me entertained. As capable and detailed as the SUI’s borderline analytical bass is bass heads craving visceral slam with bombastic mid base and rumbling sub bass will be disappointed. The SUI bass wasn’t tuned for bass heads it was tuned for detail loving listeners who instead crave depth, speed and note separation in their bass.

The SUI‘s mids are its second greatest strength. The SUI operates on the mids like a precision surgical tool. As mentioned above, the mids are slightly laid back in comparison to the bass and treble, giving the overall sound signature a slight V-shaped quality. Though laid back, they are still quite engaging and offer up excellent micro detail and clarity. Guitars, horns, and strings are quick and clear and music recorded with very foreword sounding vocals no longer sounds like the singer is shouting in your face. Although walking the line on analytical with its energetic upper mid range the mids are still able to present an enjoyable musical like experience and with a lot of my music mid frequency presentation, for the most part, sounded quite fluid and bordered on neutral. Tonality, not the most natural sounding mids especially when listening to badly recorded source. People who enjoy a more tonally correct warmer mid range will be left wanting.

The SUI‘s highs are some of the best I’ve ever heard — second only to the far pricier Tralucent Audio 1Plus2 (reviewed here). Its treble is very extended, forward and highly aggressive — giving the earphone a spacious and lean sound. Because of its tuning, this little piece of gear is extremely revealing, so badly mastered, overly compressed music will sound harsh and sibilant. People sensitive to overly forward, aggressive treble will not like these earphones. If there was one thing I would change about the Flat-4 SUI, it would be to slightly smooth out the lower highs and just tame the upper mids to control sibilance better.

The SUI is Ocharaku‘s entry-level earphone. For those looking for a more refined version of the SUI sound, Ocharaku also offers the KURO and its flagship, KAEDE, both of which supposedly sound more tonally correct. Personally, I loved listening to the SUI and was marveled by its technical capabilities. For those looking for an IEM with a huge sound stage, high retrieval of micro detail, and aggressive, airy mids, the SUI is a must buy.

TheDigitalFreak is an middle-aged music and (C)IEM enthusiast born two decades before his time. He views being labeled an audiophile by his peers a joke yet loves to mix and match gear in order to attain different types of sonic coloration for his music. Above all, he tries not to lose sight of the joy music provides; it is ultimately what matters, rather than the gear playing it.
(Full Author Bio)

2 thoughts on “Thoughts On The Ocharaku Flat-4 SUI”

  1. Thanks for yet another excellent review. It sounds like these phones are definitely not for me.

    That said, what source are you using with the RX MK3 in the review (it looks like some sort of iPod)? I’ve found that combo to be a little bright with some of my more analytical sounding phones (CK10, DBA-02 mk2).


Leave a Comment

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s