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!