64 Audio (1964 Ears) ADEL U6

64 Audio U6

Disclaimer
These U6 are on loan from @ostewart of Sound Perfection Reviews and will be returned afterwards. I am not being compensated for this review in any way. Also, I have not done a lot of reviewing, so be sure to check out Oscar's review for a more experienced perspective.

64 Audio U6

• 6 balanced armature drivers
• 2-low, 2-mid, 2-high
• Quad Bore Design
• Integrated 3-way passive crossover
• Impedance: 22Ω @ 1kHz
• Sensitivity: 115dB/mW
• Freq. Response: 10Hz – 20kHz
• Noise Isolation: -20dB with apex m20 module, -15dB with apex m15 module

Links:
http://www.64audio.com
https://www.facebook.com/64audio
http://www.soundperfectionreviews.com

64 Audio
Sound engineer Vitaliy Belonozhko founded 64 Audio as 1964 Ears in 2010, naming the company after "a pinnacle year for Rock music" and a historic year in audio innovation. Their first IEM was the 4-driver 'Quad' and since then the company has evolved considerably. Not only has the driver count gone up from 4 to 18 in their latest TOTL A18/U18, they have also produced a number of other interesting technological innovations. Most notably in 2016, a year after their rebranding to 64 Audio, their APEX, Air Pressure EXchange, and TIA, Tubeless In-ear Audio, technologies. The latter technology was incorporated in their most prestigious (and expensive) model to date, the coincidentally also 4-driver, tia Foutré. History has come full circle!

Background
My interest in the U6 and 64 Audio in general came from their APEX technology and the 64 Audio 'house sound', which I understood to be quite warm and smooth. I like warm and smooth. I enjoy hiding myself away from the big bad world in a comfortable blanket of warm sound. My own private little bubble. And I don't want that bubble to burst because of sharp treble or so much detail that a London Tube at rush hour feels calm in comparison.

APEX comes in because I used to have CIEMs and after only a few weeks had to have them reshelled to universal fit because they caused all sorts of pressure-related issues (through no fault of the manufacturer, btw, I'm just weird). Since then my ears have become quite sensitive to pressure changes and I was very curious to see if APEX could help there. I also listen to a lot of classical music and due to the slightly open nature of the APEX module, I was also curious to find out if that would make symphonies sound more airy and natural.



Build quality and fit
The U6 come in a very nice case that has special compartments to protect the IEMs individually, as well as convenient places for the cleaning tool, shirt clip and any extra Apex modules you might have. All this protection is very nice, but the build quality of these IEMs is excellent. They will probably be able to stand up to quite a bit of abuse, but I babied them nonetheless because they were not mine.

The fit is generally excellent and should suit most people very well. My only point of concern was the long length of the stem that caused some discomfort to my ears after (very) long listening sessions. This probably has to with my canals narrowing more than usual. Nothing too bad and I still managed to use them extensively for my review. Were I to buy my own U-series, then I would consult with 64 Audio if it was at all possible for them to cut a tiny bit off the stem to optimise comfort.

Source
All listening was done with my AK70, a neutral warm DAP that is more organic in how it presents the music, rather than analytical. Listening was done with the M20 module and stock cable.

Presentation
The U6 present quite a large and natural sounding stage that is in part the result of the APEX module. They are characterised by a smooth and non-fatiguing presentation that is of a high quality, a quality that might not be apparent upon first listen. What jumps out is a strong prominent mid-bass, which is compensated by a quite linear, perhaps slightly attenuated, but well extended treble. The resulting image has a sophisticated smoothness; it retains plenty of detail, but the U6 present that detail with velvet gloves. Not weak, mind you. The U6 are bold and confident with quite thick notes and a stable image with clear positioning of realistic sounding instruments. This is a signature that is fun and enjoyable all day long, as it is as non-fatiguing as it gets.

The main consequence of the presentation is that there appears to be a very thin veil over the signature, meaning it takes a while before the details start to become apparent. This is certainly very enjoyable and hardly noticeable with music such as indie rock, but sometimes causes just a bit too much smoothness in delicate string sections of classical music. For vocal jazz such as Madeleine Peyroux though it is great, as it sets a lovely warm and intimate feeling stage.

Despite the intimate feel, the stage is large with good depth, which aids in separation. Because of the thicker note size the depth helps with the separation of more complicated pieces of music such as classical symphonies, but occasionally the layers will obscure one another a little and cause some congestion during very challenging sections.

Bass
The U6 have a strong and full-bodied mid-bass that is well controlled, detailed and adds delicate warmth to the entire signature. With the M20 module it has a dominant presence in the signature, not bass head dominant, but enough to create a fun and engaging signature that works very well with, for instance, the energetic rock from Imagine Dragons. During the song "Thunder" the U6 will make it impossible to sit still.

The sub-bass reaches quite deep and again works very well with rock and dance music, giving a strong impact that emphasises the rhythm set by the music.

For classical music this is all a bit too much, but I couldn't help but enjoy the Nutcracker here. There is a section I often use to test the bass performance of IEMs and that is when the clock strikes twelve and a fight breaks out between the Nutcracker and the Mouse King. At this point the piece becomes very dark and oppressive and the U6's presentation of this is nothing short of spectacular. I had the biggest smile on my face! The dominant mid-bass rolled in from the back of the stage like dark clouds looming over everything else and the sub-bass impact further emphasised this dramatic moment. Key here was the amount of control the U6 had over this dominant bass presence. Everything else was still there, but the whole image darkened and became oppressive with tangible emotion. It was a deliciously naughty treat and really showed off how capable the U6's bass is.

Mids
The mids of the U6 are really quite impressive, but it takes a while to be able to appreciate just how good they are. The mids are warm and smooth and this is what comes across most clearly, yet after listening for a while details start to emerge and the listener is treated to vocals and instruments that sound natural and are full bodied. This works exceptionally well for smooth vocal music such as Madeleine Peyroux. The U6 create an intimate atmosphere where her voice is like a whisper in your ear and well-positioned, accurate sounding instruments complete the image of a jazz club with the listener in prime position. I would say that male vocals, such as Eric Clapton, sound more natural than female vocals, which have a hint of warmth to them.

Although the U6 are not the ideal choice for classical music, they are still very capable of dealing with complex symphonies and most notably because instruments sound realistic. There is a good distinction between similar sounding instruments such as the flute and clarinet. Such instruments often work in harmony and when playing the same note can be difficult to distinguish. The U6 do this well and it helps to more accurately portray the nuances of a particular piece and its interpretation by the conductor. That the U6 are not an ideal choice for classical music is most clearly illustrated by a complex and layered piece such as Brahms' symphony No.4. The multitude of layers is a bit too much for the U6 to separate properly and causes some congestion. Still, the symphony retains a harmonious sound, which is quite a feat because it could have easily sounded disjointed.

Treble
The treble seems quite linear, although perhaps a bit attenuated, and well extended, which, in combination with the prominent mid-bass, results in the U6's characteristic smoothness. This smoothness is very clear in the treble, which is even and has a hint of warmth to it that makes it pleasant and inoffensive. I would not call it a sparkling treble. There is certainly a quality treble, but it is pushed into the background a bit. To return to the Nutcracker, I find that some of the fairy-like sparkle is missing and as a result a key part of the characteristic emotion of the piece is lost. Likewise cymbals in heavy metal are pushed somewhat towards the background, creating a much darker sound.

I am sure I could easily live with it, but the U6 have a lot of potential for fine-tuning that is hidden beneath that thin veil and uncovering it is quite easy. Whether or not this is an interesting route to go down depends on musical preferences and I will do my best to illustrate the trade-offs versus the stock sound.



M20 vs M15
The most obvious means of fine-tuning the signature of the U6 is of course by switching from the M20 APEX module to the M15. As the specifications indicate, the M15 are a little more open and the isolation is reduced from -20 to -15dB. This is still a decent level of isolation and in return you get a larger and more airy stage, and the mid-bass is toned down a little with the sub-bass not hitting quite as hard. This is a more balanced sound and it reveals more details in the upper mids and treble, such as the texture of strings, helping violins sound less smoothed over. There is also better separation and this means that the U6 perform better at classical music, although still not optimal.

Female vocals sound more natural as that hint of warmth is removed, but this comes at a cost. Rather than sitting up front and centre at a performance by Madeleine Peyroux, you are placed a bit further back. More details come through, but that warm and intimate setting is not quite as strong anymore. For that I prefer the M20, for everything else I find that the M15 offer a better balance while still largely retaining the warm and smooth sound of the U6. A great advantage of the M15 is that they show off the natural sound of the instruments a lot better.

Cables
Fine-tuning the sound of the U6 beyond switching between APEX modules can be done with high quality aftermarket cables that offer a number of advantages. I personally do not like the stock cable for its memory wire, it is just a bit too stiff, and aftermarket cables can have greatly improved ergonomics. Cables now also have clearly defined sound characteristics and it opens up the option of using a balanced out if your DAP has one. 64 Audio have recognised this as well and offer a Premium cable of their own, which is a silver-plated copper cable with options for either 2.5mm or 4.4mm balanced termination alongside the normal 3.5mm single ended.

I only had two cables at hand: the Effect Audio Ares II and Eros II, and both were balanced. The balanced out on my AK70 provides a warmer and more laid-back sound with an increased soundstage, especially in depth, a darker background and improved imaging.



-Effect Audio Ares II (balanced, M15)-
The Ares II is an atypical copper cable that adds some brightness and improves treble extension. Adding the Ares II creates a very engaging sound with a holographic stage. The mid-bass gets a bit more presence with the M15 and the sub-bass hits deep again, but unlike with the M20 and stock cable there is no veil, instead the sound gains a lot of clarity and even sparkle in the treble. It is a bit warm for classical music, but the increased stage, blacker background and slightly thinner note size, mean the positioning and layering is greatly improved. Now the U6 handle Brahms' No.4 with ease and the instruments sound even more realistic with strings getting a lovely texture and definition to them. It is very much a warm, fun, and above all effortlessly natural sound, although because of the large stage it does not regain the intimacy of the stock U6 with M20.

One of the things I love with this pairing is listening to Astronaut Ape, a type of mellow EDM with lots of bits of sound throughout the stage. It really benefits from the large and holographic stage and when I first listened a didgeridoo came in that blew my mind. There was so much texture and detail to that low, guttural sound that I could almost feel it in my stomach. Absolutely gorgeous!

Is it still smooth? Oh yes, very much so! It is not the velvety smoothness of the stock U6, but I am notoriously sensitive to any sharpness or too forward details and I could listen to this pairing for days... In fact, I quite happily did!

-Effect Audio Eros II (balanced, M15)-
The Eros II is a silver-copper hybrid cable, where two of the wires are pure copper and two pure silver. When I first tried this pairing I was listening to classical music and it sounded a lot cooler than with the Ares II, this made me a bit concerned about other types of music, as I had really enjoyed Caro Emerald's Acoustic Sessions, the soothing vocals of Madeleine Peyroux and the impactful bass of Astronaut Ape. I needn't have worried because as soon as I put on Caro I was tip-tapping away to the wonderfully textured instruments and clear vocals, Madeleine's vocals too were clearer, but still intimate and warm. In fact, with Eros II the U6 do vocals exceptionally well! Vocals have fantastic clarity and emotion to them.

Remember that didgeridoo? That guttural sound was even deeper, with more texture and still a lot of air. The same goes for the other end of the spectrum. The treble had become airy and detailed with cymbals getting a nice shimmer and more presence. The stage was bigger still and this greatly benefitted the layering, yet the U6 still retained an intimate sound. Not as strongly as with the M20 and stock cable, but with the outstanding vocals the U6 still had something cozy. With Eros II the U6 walk a fine line between having a sense of intimacy, being organic and natural on the one hand, and becoming analytical and detailed on the other. It works exceptionally well and I absolutely adore it!

Eroica
This section is specifically aimed at illustrating how well the U6 scale with classical music. It is intended to provide a sense of how somewhat illusive aspects such as tonality, imaging and resolution can affect how the emotion of a piece is presented. To do this, I will focus on the first two movements of Simon Rattle's modern and energetic interpretation of Beethoven's No.3 'Eroica'.

With the stock cable and M20 module the first movement is very smooth to the point that violins lack the bite and texture to provide the piece with energy. Because of this and the elevated mid-bass, the tympani becomes the dominant source of energy for the piece and it makes it sound slower and heavier.
In the second movement there is a section that builds up gradually, starting with one set of violins, then another and slowly lower tones are introduces such as cellos and the tympani, while at the same time brighter instruments such as the flute and trumpets are used to add to the drama building up. However, the stock U6 become congested through the many layers and especially the brighter instruments are unable to rise far enough above the rest to capture the emotion and thus much of the drama is lost.

Switching to the M15 changes the balance. The reduction of the mid-bass pushes the tympani further back and improves the texture and energy in the violins. Because the violins become the dominant source of energy for the piece, the overall speed is improved and this adds excitement to the fast first movement.
The tonality of instruments, especially woodwinds, is improved and there is overall more air to the stage and better separation. Despite this the second movement still becomes congested and the brighter instruments are still lost in a sea of sound.

Adding the balanced Ares II to the M15 really makes a difference. The stage is larger still, the note size is a little smaller, the background is blacker and the image is even more stable. The tonality of instruments is greatly improved and the resolution is higher. All these elements contribute to the violins getting their characteristic bite when the bow hits the strings with force and conveys much more energy, yet the tympani has added impact and control to work in great harmony with the strings. It makes the first movement incredibly engaging and energetic.
The second movement starts slow and has a lot of solo sections that are presented very well. The instruments sound lush and realistic, and their emotion is conveyed effortlessly, while transitions between instruments are clearly defined yet smooth. There is still some congestion as the drama builds up, but trumpets now sit well above the rest with authority and I noticed other, more delicate bright instruments coming through that I had not heard before. All these added layers build up the sense of drama and scale of the piece and make it thoroughly enjoyable.

Replace the Ares II with Eros II and the U6 become very balanced, the stage is opened up even further and more details come through. Some of the energy in the first movement is lost due to the cooler signature this creates and it changes the presentation from engaging and fun to serious and more accurate. Instruments have a bit less body to them and no longer sound quite as lush, but in exchange more details come through and the extra air helps during more layered sections.
During the solo sections of the second movement instruments sound more refined rather than lush, but still accurate and effortlessly natural. Once the drama builds up the extra separation and the more airy stage presents the build up more seriously and to my ears more accurately reflects the emotional intent behind the piece. It is very dynamic without any excess. Revolution after all is a serious business and not meant to be "soap opera"-like drama. With Eros II the U6 sound grown up, like they have lost their youthful exuberance to become more focused. For classical music this is clearly the technically best pairing I have tried and the U6 perform impressively well like this.



APEX
As someone who has had pressure related issues I was naturally very curious about the effectiveness of the APEX modules. After having used the U6 for a while now, I am very happy with how they work. The modules certainly relieve some pressure and, more importantly, help avoid pressure fluctuations. That has made the U6 very comfortable to wear for long periods, except of course in my case for the slight discomfort caused by the longer stem. Isolation is also still quite good. Not as good as my universal Ei.3, but still capable of creating a lovely bubble to block out environmental noise and hide myself away in.

Conclusions
The U6 are very impressive IEMs with a high degree of versatility. The stock U6 with M20 have a unique type of velvety smoothness to them that I always feel the need to describe as "sophisticated". I absolute adore my smooth Custom Art Ei.3 and the U6 are a much more mature version of those. They have a great tonality and offer up spades of detail, and yet somehow 64 Audio have managed to give them a very even smoothness throughout the signature that create a warm intimate sound that is still set in a large stage.

The option to fine-tune the U6 with the APEX modules and various cables makes the U6 very versatile and capable of dealing with every kind of music you can think of and they will excel at it in an effortlessly natural way. Priced at $899 they are not cheap and the M15 modules will need to be bought separately, but they still offer very good value for money and I think that says a lot about just how well these perform.

Firstly I would like to thank 64 Audio for sending me this sample, they were really helpful picking the monitors they thought would suit my music tastes and have excellent customer service. These have had well over 100hrs of burn-in, no real differences were noted.

Gear Used: Audio Opus #2 DAP > U6
Dell desktop > Topping D30 > HeadnHifi O2 amp > U6



Tech Specs:
6 Balanced armature drivers (2x Low, 2x Mid, 2x High)
3-way passive crossover
apex M20 module
Impedance: 22 Ohms at 1kHz
Sensitivity: 115dB SPL @ 1mW
Freq. Response: 10Hz – 20 kHz
Noise Isolation: -20dB with apex M20 module
https://www.64audio.com/product/1964-U6-Earphone

Packaging, Build quality and Accessories:
The U6 come in the same packaging as the rest of the 64 audio range, custom and universal. It is a small rectangular white box with a big picture and the brand logo on the front, and the company’s story and a bit about the Apex technology on the back. Slide off the outer sleeve and you are presented with a red inner box that has a flap with a picture of a vocalist on it. Lift this up and you’ll find the box which has the monitors and accessories in it, on the underside of the flap is a quick start guide on how to insert them properly and also a bit about safe volume levels. There is a small white tray above the box that holds the tips. The packaging is really slim and looks great; it is simple yet eye catching.


The U6 are built like the rest of the range, and that means they are superbly made. Each side is flawless with no visible seam between the body and faceplate, the 2-pin sockets are tight the cable is the standard affair you get with most monitors but this one has 4 separate cores. The cable is nothing special with good strain relief, but this is easily swapped out too. The Apex modules are very precision pieces and look excellent, everything just feels really well put together.

Accessory wise the U6 come with a 64 Audio hard case which has separate compartments for each earpiece, along with holes for extra Apex modules, and a part for the cable clip and wax cleaner. The case is really nice, and has a pot of silica to absorb moisture and prolong the life of your monitors. Included tip wise are Comply foam tips in S, M and L, along with a pair of bi-flange tips, I personally like a wide array of tips so this could be improved upon. However the comply tips are really good and most will be able to get a great seal with them. Also included is a cable clip and wax tool, so overall a complete package just missing some extra tip sizes in my opinion.


Comfort, Isolation and Apex Technology:
Now I have tiny odd shaped ears, so the left side fits really nice and flush, with the housing fitting into my cymba as it should. The right side however gets pushed out of my cymba due to my awkward ears. This does not affect the sound or seal, and they are superbly comfortable, they just look a bit odd. They will fit the majority of people with normal ears fine, as I have had these issues with other IEM’s too. I find Comply tips to be very comfortable, but I prefer silicone with these for sound reasons, I have some XS spinfits on them and they fit securely and are not causing comfort issues at all. I personally prefer cables without memory wire, but the stock one is perfectly acceptable.


Isolation depends on the Apex module used, the stock is the M20 which offers -20dB of isolation, this is a great all rounder and offers a good deal of isolation but not on par with fully sealed IEM’s. Using the optional M15 module you get -15dB of isolation, but also slightly different sound. Different sounds and levels of isolation are just one of the benefits of the Apex technology.

Now I won’t go into detail about the Apex technology, so you can read here:https://www.64audio.com/technology

“When you seal a miniature speaker in an ear canal, the air inside becomes trapped. As the speaker produces sound it moves the air and causes the ear drum to work excessively. The pressure exerted on the ear drum causes ear fatigue, also known as listener fatigue.
By way of a pneumatically interactive vent the apexTM Technology (Air Pressure Exchange) relieves this pressure. With apex the sound is also dramatically improved across the spectrum, the soundstage is more expansive than ever before, and the technology is versatile allowing for a selection of isolation levels — all while minimizing ear fatigue.”

How much of a difference this makes, I am not sure, I did find that they never became fatiguing over long listening sessions and you can push them a little harder than normal IEM’s, however I am careful with my volume levels so haven’t tested at high volumes for longer periods of time.


Sound:
I will split this into the main stock sound with spinfit tips and M20 module, I will then write a little on the M15 module and other cables.

Lows: The power and impact the lows have on these is really impressive, what is more impressive is how controlled they are, never getting in the way of the rest of the sound. One of my first thoughts was wow, these really extend low and those thoughts have not changed, you can really hear the sub-bass rumble on tracks with these.

The bass is not overly boosted, having a slight lift with excellent dynamics and punch. They can really hit with authority, kick drums don’t sound hollow or flat carrying air with each thump. Bass guitars really cut through the mix, being easy to distinguish and follow.

I fear that I am making the lows sound like they are boosted and that these are bass heavy, but they are not, it is just the power behind the lows is very good.

Getting the lows to have the dynamic punch these have, with speed and agility yet still retaining fullness and impact is not an easy feat for dynamic drivers, let alone BA drivers.

Mids: The mids cut through with excellent texture and tone, they are not clinical and don’t ever sound thin. Guitar tones are powerful and real, with excellent imaging and separation never sounding congested. Male vocals are a treat on these, listening to Thrice, Dustin’s vocals sound pitch perfect without any additional flavour being added by the IEM’s.

Every pluck of a string and finger slide on a fret board is heard in acoustic recordings, giving an intimate performance that allows you to hear subtle details without fatigue.

The U6 can handle both male and female vocals well, but male vocals come across a slight bit better due to a slight dip in the upper midrange. The slight dip in the upper midrange means that there is no sibilance or glare and these remain completely fatigue free. The most impressive part is how the lows are full and dynamic, yet never seem to affect the lower midrange.

Highs: The dip in the upper midrange/lower treble region takes away a little bit of the initial impact of cymbal hits and thus the treble seems a little bit tamed and behind the rest of the sound. This is true; the highs do take a backseat somewhat but once you get past the initial impact there is really good detail and air with impressive extension.

The highs are not upfront and in your face, but they are very well placed in the mix when it comes to imaging, and there is still plenty of resolution up top that really shines when listening to well recorded music. Even when the music gets busy the highs are never masked or subdued, they are always there adding some sparkle without fatigue. Again I will add that the tonality of the highs is very good with them sounding very natural without a hint of grain or metallic sheen.

The separation on the U6 is excellent; they have a warmer thicker sound with the M20 module but still retain good layering. The soundstage is also a strong point of the U6 being spacious and wide, with great imaging and plenty of out of head experiences depending on the recording.


M15 Module, 64 Audio were kind enough to provide me with a pair of M15 modules to compare the sound of each. I won’t go in depth like above but I will try and describe the key differences.

First off we will start with the lows again, with the M15 module the lows lose a little bit of the thicker tone that the M20 offers, they become a little less full but gain a bit more control. The lows don’t hit with as much impact as the M20 module, but they are slightly quicker and cleaner. The mid bass is slightly more prominent over the sub-bass now.

The midrange gains a little bit more air and separation, the tonality is still spot on just they now sound a little more open. Detail is still the same, but the extra separation means they are easier to pick out.

The highs are still smooth and fatigue free, however the extension feels a bit more effortless and the is a slight bit more presence. They are still far from being bright, but sound a bit more balanced with the M15 module.

Overall the M15 module tones down the sub-bass a little without losing extension, the lows are also a little bit leaner and more in line with the rest of the frequency response. The mids gain some extra air around notes and better separation, and the highs gain a little more presence without any additional peaks. They still retain a smoother sound in general, but sound a little more linear with the M15 module over the thicker more impactful sound of the M20 module.


Cable wise, I know many people do not believe in differences; however I believe they can make a small difference and that synergy is key.

I have a homemade Toxic Cables silver plated copper cable, and also an Effect Audio Ares II on hand and personally prefer the toxic cables one. I found that using that cable with the M20 module, the lows tightened up a little with some added sparkle up top. The separation also got a little better; these are small differences but added to my overall enjoyment of the U6.

The Ares II adds some sparkle, but I found that I wanted the lows to be a little more controlled which it does not offer, it retains the full bodied sound of the stock lows. With the M15 module the Ares II works very well, the soundstage is also a little enhanced with it, but I think I still prefer the M20 module + Toxic Cables sound, it is tight, balanced and non fatiguing.


Conclusion: $899 is a lot of money to shell out on headphones, add a little more if you want the M15 modules, but you can really tweak the sound of these with cables and modules if you like. The stock sound with the M20 module is thick, smooth and yet still with plenty of detail to be heard. They offer a warm and non fatiguing sound that a lot of people will enjoy. The power that the lows have to offer and the pitch perfect midrange is stellar yet I found myself craving a little added sparkle.

By just swapping out to the M15 module, the U6 offered a more balanced listening experience without any added peaks or harshness. They still offer a smooth slightly fuller sound sound with the M15 module, but it gains better balance and control, with a bit more air at the expense of a little bass impact. I highly recommend listening to the U6 if you can, as it is an excellent IEM in its price range and the build quality and customer service is all excellent.

Sound Perfection Rating: 9/10 (Smooth, non-fatiguing, pitch perfect mids, realistic bass, layering and detail retrieval, ability to tune the sound with Apex modules)

---

Before I start my review, I would like to Thank 64 Audio and Asius Tech for providing me with a review sample in exchange for my honest opinion.
 
Manufacturer product website: https://www.64audio.com/product/1964-U6-Earphone
 
* click on pictures to expand
 

---

 
It's never easy to work on a review of another in-ear monitor model after doing in depth coverage of the flagship from the same manufacturer.  I was very impressed with a sound tuning and ADEL technology behind 64 Audio U12/A12 flagship which I covered in my review HERE, but afterwards received a number of questions asking how it compares to one of their mid-tier models featuring half of the driver count.  The price/performance ratio topic always gets a lot of attention, and I'm starting to notice that more people, who previously got caught up in a tangled web of driver number wars, are now taking a step back to re-evaluate their priorities.
 
You also have to be realistic about the law of diminishing returns, but in case of the latest 64 Audio A-/U-series models, regardless of the number of drivers or the price or the custom vs universal fit, they all feature innovative ADEL technology that acts as a secondary eardrum to absorb the harmful pneumatic pressure and to reassure a safer listening while avoiding the risk of hearing damage.  Since I already covered about 64 Audio and Asius Technology (creators of ADEL) in my original U12/A12 review, please use it as a reference for addition info.  The intent of this review is to focus on their 6-driver U6 model, and to go into more details about its performance, comparison, and pair up.
 
As a spoiler, I want to say ahead of my write up that if you are expecting a conclusion with "Don't waste your money on U12 because U6 is almost as good" – it’s not going to happen because no matter how you look at it, the U12 is still a flagship in its full glory.  But U6 sounds great as well, and got one important trick up its sleeve where some might even consider it instead (or maybe in addition to) of U12.  Want to find out more?  Then, let's move on to the review!
 
Unboxing and Accessories.
 
Even so I wasn't planning to cover the info already mentioned in my original U12/A12 review since the packaging is identical, I can't help myself but to gush over it again.  Regardless of the model or the paid price, everybody is treated like VIP with a compact packaging box that has just enough room for a 64 Audio custom travel/organize case, portable dehumidifier container (goes inside of the case), and 64 Audio sticker.  If you are receiving Universal series version, you will also get a pair of Comply foam eartips in S/M/L sizes and a pair of medium double-flange silicone tips.
 
The cover of the packaging sleeve features a company logo with a picture of monitors corresponding to either Universal or Custom fit design.  When you slide a sleeve off, you will see a flap with a picture of a performer and “Hear Everything” underneath – what to expect when using 64 Audio monitors.  Where it gets more interesting, once you lift the cover flap up you will find a Quick Start Guide with a lot of great pointers about headphone listening safety, volume advisory and proper way to put in-ear monitors in your ears.  Right from the start you get a sense of 64 Audio and Asius Tech really caring about your ear health, one of the main benefits behind the featured ADEL module.
 
I did mention that everybody is treated like VIP, but don’t expect champagne and caviar - instead you will get one cool custom case.  Everything from a wide easy to handle latch to an air valve eliminating build-up of inner case pressure when you close it, from an individual earpiece storage areas with removable rubber lining to a custom built-in cable winder, and including a place to plug right angled headphone jack and to place a round dehumidifier container, as well as a cover with a built in organize to hold securely a shirt clip (included), a cleaning tool (included), and up to 2 sets of ADEL modules – everything is custom tailored and well thought of.  There is even enough room for a thicker replacement cable, though a straight jack will not fit into right angled storage pocket so keep it along with a cable.
 
When you placing the order, you can also specify to etch your name on top of the storage box to personalize it.  While everybody uses an off the shelf Pelican or Otterbox storage cases with a pre-cut foam insert, 64 Audio went one step ahead with their own custom designed case which protects your headphone investment and keeps everything organized inside of it.
 
Unboxing.
 
 
 
 
 
Accessories.
 
 
 
 
 
 
 
Cable.
 
All 64 Audio IEMs/CIEMs feature a replaceable cable with a standard universal 2pin connector, reassuring you can use different after market cables to customize the appearance and to upgrade the sound.
 
If I'm not mistaken, the bundled stock cable was actually updated and now features a more durable design.  The cable utilizes a regular OFC wires in a tight soft black rubbery jacket, with 4 separate twisted conductors keeping L/R ground connection separate going into the right angled gold plated headphone jack with a nice rubbery housing and a decent strain relief.  The y-splitter is just a piece of a shrink wrapped tube and chin slider is a clear short piece of the tube as well.  This chin slider has a good friction and doesn’t feel loose.
 
Next to the 2pin connector you have a piece of flexible memory wire in a soft shrink wrapped tube, and the connector itself has a red/blue dot to indicate Right/Left designation.  With a pre-shaped memory wire, there is no worry about mixing the polarity of 2pin connectors between earpieces since it has the same orientation, but when dealing with replacement cables – polarity of the connector has to be consistent, both pins facing the same way especially when you don’t have a memory wire.  Also keep in mind, universal series models only have a surface mount socket because there is not enough room for a recessed one.
 
 
 

 
The stock wire does its job and seems to be built ok.  But in case of U6 with replacement cables the sound change was noticeable enough for me to switch and never look back.  As my usual disclaimer, not everybody believes or hears the audio benefit of replacement cables.  I’m not trying to convince anybody, but rather sharing with you my personal experience.
 
U6 has a very impressive sound tuning, but with a stock cable and even some silver plated (SPC) replacement cables I felt that performance was held back, especially when it comes to mids.  I went back’n’forth numerous times, listening from different sources, even at different times of the day just to make sure my mind is not playing tricks on me, and I consistently came to the same conclusion that a stock cable makes mids sound flat and a bit dull.  But once I replaced the cable with pure silver wires – not only did bass become more articulate and tighter, but also mids came to life with more sparkle and better dynamics.
 
I actually hear the improvement in audio performance not only with pure silver, using Whiplash latest TWag v3 T (Teflon) series, but also with pure copper (TWcu) cable where it added a little more texture to the low end.  Trying it with Litz SPC (Linum) or regular SPC (Noble cables) had a more subtle effect, but not as noticeable as with other two cables.  Just keep in mind, as much as I enjoyed the sound improvement with TWcu – it's 8-conductor braided cable where you are dealing with extra weight and reduced cable flexibility.  With TWag v3 T-series, the silver wires are thinner and more flexible, and it’s not an issue that Whiplash doubled the number of conductors to 8.  But be prepared to deal with some serious microphonics effect, especially amplified by ADEL module due to reduced isolation.  I’m actually found that TWag v3 T-series sounded better than TWag v3 and TWau when paired with U6, but I had to use an electric tape wrapped around R/L sides of the cable between the memory wire and the wooden chin slider.  That reduced microphonics significantly since the cable was no longer rubbing against my chin.
 
Cable replacement is not a must have upgrade, and I don’t expect everybody to hear the same level of improvement as I have.  But for me personally, after trying U6 with different cables and settling on the one with pure silver conductors – I didn’t want to go back to a stock cable.
 
Whiplash (TWcu and TWag v3 T-series).
 
 
 
Design.
 
My U12/A12 review covered Custom IEM experience where I used 64 Audio on-line Designer to customize A12 and then enjoyed on-line tracker which keeps you up to date with every single step of the design/manufacturing process as you wait for CIEM.  With Universal IEM the ordering process is a lot simpler since everything is already preconfigured and you don’t need to customize anything.  It’s not exactly an instant gratification since you still have to wait a few weeks, but typically the wait time is based on the current queue of orders rather than delays associated with a custom model build.
 
All Universal series models have a similar design shape and use hypoallergenic hard acrylic material.  They all have a non-transparent solid piano black finish with “ADEL” printed on the right earpiece and “64 Audio” emblem on the left earpiece.  The faceplate is flat, and the overall shape kind of reminds me of a guitar pick with one trimmed side.  While the faceplate side of the shell has a more defined edge, inner side of the shell is more rounded and smoother.  The nozzle is quite extended and at 8mm probably the longest among my other IEMs, but that reassures a deeper insertion and a more secure fit, at least for my ears.  Also, the nozzle has a slightly thicker part in the middle where 64 Audio etches a number corresponding to a driver count, plus this thicker part helps in keeping eartips from sliding off.
 
The nozzle has a quad bore symmetric design where 3 of the bore openings go to sound tubes connected to corresponding clusters of 2-low, 2-mid, and 2-high balanced armature drivers, and the 4th bore opening goes to ADEL module cavity which is aligned opposite of the nozzle on the faceplate.  Even so nozzle is extended, it feels pretty sturdy.  Obviously, the internal design of each shell has 6 balanced armature drivers partitioned in 3 groups of 2, and also an integrated 3-way passive crossover.  The impedance of 22 ohms reassures compatibility with many different sources, but sensitivity of 115dB means that some low level of hissing to be expected with more powerful sources.
 
Though the thickness of universal series shell is relatively slim, it still sticks out a bit out of my ear meaning no luck with falling asleep while wearing these.  Another thing to keep in mind, even so all universal series models have the same exterior shape and finish, U12 is thicker in comparison to accommodate twice as many drivers, but we are only talking about a few extra millimeter of thickness.
 
Design.
 
 
 

 
U12 vs U6.
 
 
 
The fit.
 

 
ADEL modules.
 
Stephen’s Ambrose Diaphonic Ear Lens (ADEL) module was a big topic of discussion in my U12/A12 review, and I’m not going to rehash it.  But definitely would like to talk about the effect of default non-adjustable S1 module versus newly introduced B1 module and the fully adjustable MAM module and how they reflect on U6 performance.
 
Unlike S1 module used in U12/A12 where default signature had a noticeable mid-bass boost, the same module in U6 accounts only for a slight mid-bass boost since this monitor has a more balanced signature.  As a matter of fact while I found the bass in U12 w/S1 to be a bit too much for my personal taste, in U6 the S1 module added a nice punch without being overwhelming.  But at the same time I felt that upper mids were slightly recessed and soundstage had an average width.  Switching to B1 in U6 reduced some mid-bass punch and made an overall sound signature more balanced which also lifted the mids.  Another very noticeable change was an improvement in soundstage, making it wider and more open in comparison to w/S1.  As much as I was enjoying the extra mid-bass boost with S1, the sound with B1 was more to my liking.  You also have to keep in mind that due to S1 dual lens design (vs B1 with a single lens) the isolation will be better with S1, and it also explains the difference in soundstage expansion going to B1 with less isolation.
 
One might question if they even need MAM adjustable module with availability of S1 and B1.  In reality, S1 sounds like a fully closed MAM module, while B1 sounds like MAM module being close to fully open.  Basically MAM module has a flexibility to fine tune the sound/pressure, including individual non-synchronous adjustment of right/left sides, while S1 and B1 are like fixed presets.  For me personally B1 tuning hits a sweet spot and I’m planning to keep that module in permanently.  Also, having a “fixed” B1 module is great for those who are OCD about MAM continuous tuning since there is no click feedback.
 
When you switch to manual MAM module and start adjusting it, you hear the effect of a subtle sub-bass roll off and also reduction in mid-bass quantity, but the change in U6 was not as drastic because you don’t have the same low end impact to begin with in comparison to U12.  Also, similar to U12, you can hear the bass being lowered, becoming more balanced as you turn/open the dial and before the ADEL module is fully open the quantity goes back up.  In U6 with MAM fully open, I hear the bass quantity being somewhere in the middle between the highest level (MAM fully closed) and the lowest level (MAM 2/3 open).  It’s not just a reduction of bass quantity, but also the effect where bass is more transparent and I hear it instead of feeling it.
 
At the current moment 64 Audio is still working on finalizing their ordering form to reflect different modules, so make sure to specify which module (S1 or B1) you prefer in the notes/instructions space when placing the order.  If you don’t specify it, they will send you S1 by default.
 
S1 vs MAM vs B1.
 
 
 
Sound analysis.
 
Once I put B1 module in and switched to a silver cable, there was no going back for me because U6 scaled up to a fine balanced signature with resolving and detailed natural sound wrapped in a smooth warm tonality.
 
Starting with a bass, sub-bass extension goes deep with a nicely textured velvety smooth rumble. The quantity is just perfect, not too exaggerated and at the same time with enough presence to give bottom end analog quality, typical of dynamic driver performance.  Mid-bass has a nice punch with a moderate speed, not the fastest attack or the longest decay.  Sub-bass and mid-bass are nicely balanced, linear in quantity, well controlled, and with analog tonality, not typical of BA driver performance.  The bass has a good level of articulation with a natural timbre, but it wasn't as multi-layered, accurate or highly articulate as I found it in U12.  As I mentioned before, with S1 module you get a little more mid-bass boost while B1 balances it out with a more linear performance.
 
Mids come alive with a silver cable, becoming more dynamic and layered, rather than being flatter as I hear it with a stock cable.  Lower mids have a smooth warm body which is not too thin or too thick, definitely a little leaner then U12, especially since you have a more balanced bass which doesn't overwhelm the mids.  Upper mids are organic, smooth, with a good retrieval of details which actually scales up with a cable upgrade.  The mids never get harsh or grainy, they stay very organic and natural, not too smooth where the details are lost and also nowhere near micro-detail level.  It's a similar phenomenon as I found with U12 drivers, yet they are smoother than a typical BA performance - it sounds smooth analog, but nowhere near the warm and congested dynamic driver performance.
 
Treble in U6 takes a little backstage due to a warmer tonality with a scaled down quantity.  It's well defined with a good clarity, but not as extended and with reduced airiness.  You definitely never have to worry about sibilance or harshness, but if you are a fan of a crispy and crunchy upper frequency details you will have to lower your expectations.  The treble details are not muted - just sound more natural and smooth.
 
The soundstage expansion is very good (switched to B1 module), with above the average width and height, and a slightly above the average depth, creating soundstage which spreads around you while still providing some intimacy.  Also, U6 has a decent layering and separation, but not as much air between the layers.  The sound never gets congested and you have a good separation of instruments and vocals, but it's not on the same level as holographic imaging of U12 flagship.
 

 
Sound comparison.
 
The question about how U6 stacks up against U12 was the most dominant one after my U12 review, thus I'm going to spend more time going over that comparison.
 
Both U6 and U12 have a similar warmer tonality, but U6 is definitely more balanced in comparison.  They have a similar sub-bass, but U12 has a stronger and more aggressive mid-bass punch.  U12 also has slightly more body in lower mids and a little brighter upper mids with more sparkle and airiness in treble.  One noticeable difference is higher level of transparency and slightly better dynamics in U12, especially when it comes to mids.  I also found U12 to have better layering and separation with more air between the layers.  And U12 also stands out with a more holographic soundstage expansion while U6 has a good soundstage expansion but not as wide and more intimate.
 
B1 module really helps U12 in balancing out low end impact and in clearing up lower mids while opening up upper mids and adding a touch more sparkle, but if you are comparing using S1 module, some might prefer U6 over U12 because of a more balanced signature and less aggressive bass.  With introduction of B1 modules, the sound of U6 and U12 scales up and at the same time creates a bigger gap between these two IEMs.  But this comparison takes a whole new turn if you factor in the audio source pair up.  U6 is not as picky and will sound great from any source, even my lo-fi laptop with a noisy built in sound chip.  In contrast, U12 is more picky and shows its superiority when using better sources like my PAW Gold or Opus#1, especially playing high res files.  But paired up with my Note 4 or my mid-fi DAPs or my noisy laptop, the gap between U6 and U12 sound quality shrinks to the point where in some cases I even preferred U6 because it was more forgiving, while U12 lost its shine and sounded a bit muddy.
 
For some reason I didn't notice this as much when reviewing U12, but it became more apparent when I reviewed and compared U6.  The bottom line: if you’re building a TOTL portable audio rig or planning to use high res usb DAC/amp (like Mojo or HA-2), it makes sense to invest extra money to go with U12.  But if you are planning to use a variety of different DAPs, or straight from your smartphone or laptop - U6 might be a more versatile alternative.  And of course, if you are on a budget, U6 has an impressive price/performance ratio.
 

 
Here is how U6 stacks up against other IEMs/CIEMs.
 
U6 vs ES60 - ES soundstage is wider and has a little more depth/height.  ES low end extension is very similar, including quantity of sub-bass and mid-bass which sounds similar to U6, but the bass has a little better layering and more articulation.  ES lower mids are leaner while upper mids are a little brighter; where in comparison U6 is smoother and more organic while ES is more revealing down to micro-detail level.  The same with a treble, where ES treble is brighter, crispier, and more airy, and with a better extension.  ES has more transparency and better retrieval of details. Overall, ES is closer in performance to U12, and similarly to U12, ES scales down when driven from lower res sources.  The decision argument between U6 and ES60 is similar to U6 and U12.
 
U6 vs W60 - both have a very similar soundstage expansion (using U6 w/B1), nearly the same width/height, while W60 has a little more depth.  Very similar sub-bass extension and quantity, but U6 has faster and tighter mid-bass and overall bass is more articulate and better controlled without spilling into lower mids, while W60 mid-bass spill a bit into lower mids. W60 lower mids are thicker, upper mids are warmer and less detailed in comparison, and treble is not as crisp, not as bright, and lacking airiness in comparison.  U6 is brighter, more revealing, more detailed, with more airiness and cleaner mids.
 
U6 vs UM Maestro - UM staging has the same width and height, but with more depth.  Low end extension is very similar, and you hear a similar quantity and quality of sub-bass and mid-bass, though UM bass is a little tighter.  Lower mids are very similar as well, but upper mids in UM are brighter and a little more revealing, in some brighter tracks even harsher in comparison.  UM treble is also a little brighter and crispier, but not a night'n'day difference.  These two actually have a lot more similarities, where UM sounds closer to U6 than U12, but it still a little more revealing and detailed in comparison to U6.  Also, similar to U6, UM pairs up good with lower res sources.
 
U6 vs K10UA - K10 staging has a similar width and more depth/height.  Sub-bass is more rolled off and mid-bass has a faster and tighter punch, sounding more BA rather than more relaxed and thicker like U6 which has a more dynamic driver bass performance.  K10 lower mids are a little leaner and upper mids are more detailed, brighter, and a little more upfront. K10's treble is brighter, crispier, airy, and more extended.  K10 sounds brighter and more detailed and revealing with more transparency, while U6 is warmer and smoother and more organic/analog.  In a way, U12 is kind of in-between of U6 and K10UA, taking the best of both worlds.
 
U6 vs Savant - Savant staging has a similar width and slightly more depth/height.  Sub-bass has the same quality but slightly less quantity, mid-bass is very similar though a little faster than U6.  Savant lower mids are nearly the same, and upper mids are a little brighter and with a little better retrieval of details. Treble also a little brighter, crispier, and has more airiness, not as rolled off as U6.  Both pair up great with low res sources.  Overall, U6 is smoother and more organic and with a little more analog-like performance in comparison to Savant which is a little brighter and slightly more revealing at the top.
 
When it comes to pair up with different sources, I already mentioned that U6 is more forgiving and not as picky if you connect it to either lo-fi vs mid-fi vs summit-fi sources.  That doesn’t mean that it will take any low quality source or poorly recorded file and make it shine.  It will reflect the quality of the source, either if it’s warm or neutral or bassier, but I still found U6 to sound good with everything, though hissing level varied.  For example, there was absolutely no hissing with AK120ii, DX80, X5ii, and my Note 4.  But I did hear a little bit of hissing with PAW Gold, N5, L5 Pro, Opus#1, and my ThinkPad laptop.
 
Conclusion.
 
I really wish I would have reviewed U6 before U12 because then it would have been in a spotlight without constant comparison to its flagship big brother.  Don't get me wrong, U6 stands firmly on its feet and proudly carries Stephen's ADEL technology.  And you can’t discount the most important factor of these multi-driver monitors – the sound quality of 6 fine-tuned BA drivers with a nicely balanced signature and resolving, detailed, natural sound that has a smooth warm tonality.  I personally recommend using B1 module if you want a more balanced sound versus S1 module if you want to enhance your mid-bass.  Also, I’m a big fan of U6 cable upgrade with silver wires which brings more excitement to the sound, especially with a more dynamic and detailed performance of mids.  All together you have one fine tuned multi-driver coherent performance that will sound great from any source and will do right by your ears health!