Ocharaku Flat-4 - Reviews
Pros: Bass lots of it - mids not noticeably veiled - good soundstage
Cons: Cable seems cheap quality - no hands free option - treble may be fatiguing for some
This is my take on the SUI version of the Flat4 Dynamic driver IEMs from Ocharaku of Japan , and is taken from my review on earphonia.com .
Ocharaku Flat-4 SUI – In Ear Tech Is Driven Further Forward
by Takeanidea

Flat-4 Sui Ocharaku Earphone

VALUE 8/10

Bass in the realms of a full sized
Sub and mid bass punch and warmth
Mid range detailed clear not particularly veiled
Treble sometimes slightly too energetic for some tastes
High end sources required for larger sized soundstage
Could be more robust build
Pairings Equipment
Hidizs AP60
MacBook Pro Retina
First Watt F6 Power Amplifier
Chord Mojo Dac
Just how many different ways can an IEM be made to look? Somehow, a Japanese Company has made their new line look like a fleet of V8 muscle cars. With a pipe running the length of the driver I  had no doubt in my mind that whoever designed these things wants to shake things up a bit in the in ear world.
The industry is moving very fast with hybrid technologies of the many descriptions jumping in at mid tier pricing levels. There are many tiny shells out there within which lie some truly astonishing achievements in what can be done with so little space.
The paradox is ;
Which one of the many patents out there is truly a new technology bringing something new to our ears?
Are we paying for the new technology or for the sophistication of the sound signature?
Armed with this rather critical approach to the radical new design in front of me , I set to put these diminutive monsters through their paces. I have some in ears which have been with me for a few years. I know the sound signature of these without putting them on. For a fair fight and of course for the pure joy of slipping into something comfortable I made some direct comparisons.
earphonia.com Ocharaku Flat-4 Sui Review
I did side by side A/B testing using my trusty Chord Mojo , put the Flat4 through a smartphone, a Hidizs AP60 soon to be reviewed on earphonia.com, also a completely over the top 50 Watts per Channel Modded First Watt F6 Power Amplifier – with an ultra revealing setup.
The Twin Equalizer Element Explained
Where many IEMs win or lose in the perceived sound quality is in the mid range. The mids produce the vocals, the strings, the keyboards ; it’s what’s left over after the drummer and the bassist have had their say.

The depth and space between the vocalist and the instrumentation is a problem that faces any tiny driver and has plagued sound engineers for many years.

In this case , Mr Makoto Yamagishiof Ocharaku , owner and head engineer , has put his unique slant on overcoming these shortfalls – he has designed a series of IEMs , each of which has their special characteristics to suit an individuals sound preferences.

All of these new designs have a pipe running from one of the driver shell to the other – creating a visible connection between the 2 drivers and leaving a chamber in the middle.

Bold thinking – but does it work?

The next stage was for me to go from research to practical. The first stage for me is to put an IEM with the tips supplied , into my ears and see what happens. From there , I can tell whether I have the right type and size to move on further at this stage to some serious listening.

This stage can sometimes take a while with some of the more exotic fits out there. For instance , an IEM I shall no doubt talk about in a different article that arrived at my door today needs one small silicon hybrid in the left and one medium hybrid tip in the right ear. Such experimenting undoubtedly reaps it’s rewards.

 Build quality

Microphonics and isolation are inherent problems with IEMs above all other types of headphone out there. Due to their lightness and proximity to the ear canal , a poor cable will produce it’s vibrations against the body and this can be transferred as a thumping sound straight into the drivers. A £1000 can quickly be turned into a £10 Earbud and it’s a humbling experience.
Thankfully , the cable does not produce microphonics ; the Flat-4 Sui earphone with a bit of working out can be worn over the ear so the weight of the cable pulling on the driver shell is almost non existent.  The isolation particularly with the Comply is first class. They are really long comply and they get right tucked in and snug.

All good so far but, hang on…
It would have been nice to have seen a mid tier cable provided with these. The cable is reminiscent of the Klipsch X11i and the Sony XBA4ip. It is perfectly functional but tends to twist in on itself easily. The discrete R marking on the driver shell is tasteful and easy enough to spot in daylight conditions. Colour coding on the cable is always welcomed but seldom done and no markings have been put on the left or right.
The pipe protrudes out from the shell , of course this is part of the design feature. The shape is not my favourite shape but the Flat4s stay in well enough. The Westone style pebble shape is what manufacturers need to be trying to implement into their design criteria.
There is no clasp after the Y bend of the cables to pull the cables tighter together under the chin , or a clasp to fit the cable against your shirt. Both of these things can help keep things from catching , essential when you are out and about. And you will want to show these Muscle Cars off to the World…
There is no hands free cable supplied – many phone users are going to be impressed with the clarity these phones will produce. At 104 dB and 18 Ohms they can go loud enough. Without hands free they will have to be disconnected to take a call on your smartphone. However these deserve better than a Smartphone though!

The first testing

The silicons supplied with the Flat4 were a reasonable fit for me but I could notice to my ears an overly airy somewhat thin sound. I quickly moved to the Comply’s in the Ocheraku Tin. They are quite long and Comply’s being what they are , they can be squeezed down to svelte proportions so they were a great fit for me and I could tell straight away that I was hearing what my ears were expecting. This appearing to have done the trick now called for some serious music listening.

First up , my review model of the Hidizs AP60 , a remarkably tiny but extremely pretty Digital Audio Player which can play up to 24/192 files. Legend by Bob Marley , in High Res 24/192 was my first stop, straight from the headphone out of the DAP.

Here we have mostly bassy tracks and male vocals with a female backing band – Redemption Song being a notable exception as a solo acoustic guitar male voice number. Bass warmth depth punch and linearity would give me my first glimpse of what success Mr. Yamagishi had achieved.


The bass was big through the Comply’s , big enough to be thinking at times I was wearing full sized headphones. The Comply’s put a slight slowness to the bass but I find this signature to give a pleasant warmth to the overall feel of my music – some purists may not agree but I find in Classical and Acoustic Music I like a slight mid bass lift to give a low end depth that isn’t present in most orchestral instruments.


The mids of the Flat4s are my favourite part. There is some real class to the depth and accuracy of the mids – the main part of the music. I could follow vocals and instruments were easer to pick out than I was expecting. There did not feel like a veil had been thrown over the mids ; there was hiss when there needed to be and enough space to pick out the odd mistake in the engineering of the track ; even on a DAP barely larger than a matchbox.


The higher frequencies are taken up by cymbals , peaks in the energy of a chorus , echoes either natural or produced using the magic of the mixing desk. The Flat4s have plenty of treble energy , even with being toned down by the Comply’s (which is after all part of their job). I did not find Legend to be a fatiguing album and my Karajan recording of Beethoven’s First Symphony was equally enjoyable. Treble presence is an absolute must to achieve a decent sized soundstage , where we can get a feel for where the musicians are placed within the recording. This gives us a feel of “being there”. Too much treble energy and the whole thing falls apart because in the worst case scenario I as the listener will be forced to switch the music off!
I decided to try some newer stuff. What could be newer than the Grand Tour? The Amazon Prime Series is into it’s 2nd week already. Needless to say with a budget of £4.5 million it’s well recorded. The Flat4s were plugged into the output of my MacBook Pro Retina. The sound of screeching tyres and revving engines was awesome. The audience was very loud and this too was portrayed with good clarity.

Having got a feel for the sound signature the Flat4s can now be plugged into my Chord Mojo and hot swapped between some similarly priced competition. First up – the Sony XBA4ips.

They have a subwoofer bass mid and high frequency driver setup. The Sony’s have a more linear bass signature without the visceral impact of the Ocharakus. The mids of the Sony’s are more forgiving than their competitor. There is less hiss present and the Sony’s still have plenty of detail to offer. The Flat-4 Sui steal the show against the opposition in the mids and there is simply more going on in the mix to focus in on and enjoy. The Sony’s had a pulled in soundstage and a nice sparkle in the higher ranges. The higher ranges were not as detailed and extended as the Flat4s.

The Klipsch X11i , now superseded by the X12i , is a tiny single armature IEM ; certainly the smallest I have come across. Klipsch has managed to get a whole lot of bass into their earphone and bass , using silicon hybrid tips , was on a par with the Flat4s. The Ocharakus had slightly more punch in the mid bass region. Mids were muffled sounding on the X11is in comparison and rolled off at the top. This makes the Klipsch a forgiving IEM for poor recordings and MP3s and they are often my go to earphone for my Ipod Classic. It can’t live with the finesse of the Flat4 SUI’s – they are good but they’re not great.


The First Watt F6 Power Amplifier was designed for driving loudspeakers. It is very expensive indeed , retailing for $3500 back in 2014. My model has been modded heavily from the original design and has an extra power supply and far more caps and higher quality components where a difference was worth the cost. It was made specifically to get the most from my HiFIMan HE-6 Headphones. The HE-6 are extremely hard to drive properly.

The First Watt amps are acknowledged as perhaps the best solution for them. The builder of this power amp is at dill3000 from headfi.org and he has a bright future ahead of him in the world of headphones and probably full size systems too. Dillan made me a special balanced to single ended plug that comes from the speaker taps to run unbalanced headphones. With a great deal of care, even IEMs can be run from this monster of an amp….
The Flat4 and Klipsch understandably well overpowered exhibited some hiss through this setup, but musical refinement was what I was looking for in this comparison. The Sony XBA4ip didn’t have too much hiss at all in the test. The Sony’s revealed themselves as being slightly veiled in the mids, the X11i’s less so and the Flat4’s undoubtedly retrieving the most detail. Although this is hardly the sensible match for an IEM it is something towards an ultimate test and it’s always fun to spend some time with.


Ocharakus have produced an IEM that can push the boundaries of what we can expect from the mid tier end of the market.

The Flat4 SUI has a balanced poise with enough bottom end to keep contemporary music enthusiasts engaged and enough detail in the mids and space in the highs to keep classical fans excited.

The balance is always difficult to achieve ; there are many more models on offer out there which will bring different attributes. The SUI could be the middle ground many earphoniac’s are searching for.
Retail Price: 

30,650 JPY (approx £220/$270/€255)


Element010e001 Φ10 mm dynamic x 2 (per single channel)
Sound method/Driver TypeTwin equalized element
Output sound pressure level104 dBSPL/mW
Frequency Response characteristics3.5 to 45 kHz(HiRes-ready)
Max. input400 mW
Impedance18 Ω
MassAbout 17 g
PlugΦ3.5 mm gold plating stereo mini-plug
Code length1.2 m (type Y)
AttachmentComplyTM foam ear tips T-200 size L (Size M is attached to the main unit.) Ocharaku Can, Instruction Manual & Guarantee

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Are you still using the Sui sometimes? I can get ahold of one in relatively good condition, but as it's old and isn't as popular as the enduring legend of the EX1000, I start to wonder, is it still good?
Compared to recent offerings, and damn, is it even better than my $50 Co-Donguri Shizuku?
Can you give comparisons?
Pros: Superb micro detail pick-up, Good soundstage and layering
Cons: Laid back vocals, can get treble hot sometimes.
Short impression is here: http://www.head-fi.org/t/642191/ocharaku-flat-4-sui-the-sound-of-tea

Bonus impressions TBC.