Earphone Review

64 Audio U4-SE

Sound Analysis.

U4-SE is based on the drivers of U4 that were originally tuned to have more emphasis on bass, but in this Special Edition version, 64 Audio decided to retune its signature. After a few days of burn in and upon closer listening, I hear U4-SE as having a balanced sound signature with a neutral-revealing tonality. Actually, in some pair ups U4-SE felt even slightly v-shaped, but it still maintained a good sound balance with emphasis on bass, as well as upper mids and lower treble. This IEM also has a good level of detail retrieval with plenty of clarity and transparency.

Starting with a bass, the sub-bass extension goes deep with a nice rumble, and the mid-bass is fast, articulate, with a well controlled impact. Lower mids are quite neutral with a leaner tonality, giving some room for a cleaner separation of bass from the upper mids. As I already mentioned, upper mids have impressive retrieval of details, with a good level of transparency, though not super revealing or micro-detailed on analytical level, but they are leaning more toward the brighter side with lots of clarity. Treble is well defined, with a nice sparkle, and a moderate level of airiness (not lacking, but just enough to help with layering and separation).

Soundstage has a good depth, and above average width. Not exactly the 3D soundstage expansion which I have been spoiled by lately while testing U18 and Fourte, but it’s wide enough to provide a realistic imaging with a convincing placement/positioning of instruments.

The layering and separation of the sound (both instruments and vocals) is good, but not exactly on the high level of other 64 Audio flagships. The sound itself is far from being congested or veiled, it just missing some air between the layers which can give a better perception of separation. But regardless of that, the sound is dynamic, detailed, with every instrument being easy to distinguish.

Overall, the sound is more revealing, but it strikes a good balance between neutral and brighter tonality, especially keeping that 9k peak under control with a stock OFC cable.

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APEX modules (M20 vs M15).

The review unit I received comes with Apex M20 modules, and you can also use an optional M15 module, but I preferred the default M20 because it offered the best isolation, the most satisfying bass impact with a nice sub-bass extension, and better focused upper mids with a well controlled treble sparkle. The only thing it felt a bit behind was a soundstage width when compared to M15.

In comparison to M20, M15 lowers the bass impact, expands the soundstage width, adds more air to the upper mids/treble which makes vocals sound a little thinner and less focused. In my opinion, M15 module open the sound more, but as a result it affects the upper mids by thinning them out to the point where I wasn’t enjoying it as much as with M20.

I also tried “carrot” slug which is a solid module, and I liked the max bass impact and detailed balanced upper mids/vocals. But going back’n’forth between M20 and carrot made me realize that I’m starting to feel air pressure build up without Apex module. This was a perfect example where I can hear the benefit of this air-pressure relief module. 64 Audio currently have only the U4-SE with Apex for sale on their website.

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Pair up.

In my pair up test with different sources, I decided to be consistent and use U4-SE with M20 module along with a stock 3.5mm OFC cable. Many of you are probably aware that original U6/U12 were optimized for higher output impedance sources (typical with performing musicians), while this Special Edition version was designed for a more audiophile-friendly performance with low output impedance sources. Another interesting thing, U4-SE has a spec with 12ohm impedance and 116dB sensitivity, which could lead to hissing with some powerful sources. To my big surprise, U4-SE was dead quiet even with PAW Gold where I intentionally dropped the volume down to zero during the playback to check for hissing. Here is how I hear U4-SE with other sources.

Plenue 2 – expanded soundstage, with a balanced signature. deep sub-bass extension, nice mid-bass impact, clear detailed mids, well defined treble with a nice sparkle.

LPG – wider soundstage, balanced signature but leaning more toward being slightly v-shaped. deep sub-bass extension with a very nice rumble, neutral lower mids, clear detailed upper mids, slightly pushed back; well defined treble with a nice crunchy sparkle.

X7ii – wider soundstage, balanced signature. deep sub-bass extension, nice mid-bass impact, clear detailed mids, well defined treble with a little more sparkle.

AK120ii – expanded soundstage, balanced signature, good sub-bass extension but a little less rumble, still a nice mid-bass impact with a fast punch, neutral lower mids, clear detailed upper mids, a snappy treble with a nice sparkle.

DX200 w/AMP2 – expanded soundstage, balanced sig but leaning more toward v-shaped, deep sub-bass rumble with a strong mid-bass punch. A little warmer lower mids, slightly north of neutral, and very organic natural detailed upper mids; treble is well defined, with a well controlled sparkle.

M2s (5 ohm out) – expanded soundstage, more neutral signature, leaner sub-bass, fast mid-bass punch but with a little less impact, neutral lower mids, clear detailed brighter upper mids, sparkle well defined treble with a little more airiness.

Note 4 – expanded soundstage, deep sub-bass, nice mid-bass punch, though bass is not a tight as with DAPs, lower mids a little warmer, upper mids are clear and detailed, but a bit pushed back, making signature slightly v-shaped, nice sparkly treble. 

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Comparison.

Using Plenue 2 as my sources, due to its neutrality, I kept U4-SE with a stock OFC cable and M20 module, and volume matched in every comparison by ear. Only 3.5mm P2 port was used since all these have a regular single ended TRS connector. Here are a few selective comparisons.

U4-SE vs U6 – U6 has a little wider soundstage, the sound sig of U6 is more neutral with a warmer tonality, while U4-SE is more balanced with a stronger, tighter, and more articulate mid-bass punch. U6 bass is more neutral and looser in comparison. U6 lower mids are warmer and with a little more body, while U4-SE lower mids are leaner and cleaner. Both have a clean and detailed upper mids, but U6 is a little warmer smoother, while U4-SE is more revealing. Also, U4-SE has more sparkle in treble.

U4-SE vs SD4s (InEar) – SD4s soundstage is wider, but the sound sig is more mid-forward (J-shaped) while U4-SE is more balanced in comparison. SD4s bass is neutral and doesn’t go as deep as U4-SE, also it’s not as tight or articulate in comparison to U4-SE. Both have lean neutral lower mids, but in comparison to brighter thinner and harsher upper mids in SD4s, U4-SE sounds more natural, with more body and more realistic timbre. Both have a well defined treble, though SD4s has more crunch and airiness, which also makes it more piercing and harsher, while U4-SE treble has more control.

U4-SE vs UmPro50 (Westone) – here, U4-SE soundstage is actually wider; both have a balanced sound sig but U4-SE tonality is more revealing. Both have a very good sub-bass extension, but U4-SE has stronger mid-bass punch. Also, overall bass is tighter and better controlled in U4-SE while Pro50 is more laid back and spills a little into lower mids. Lower mids are leaner and more neutral in U4-SE while Pro50 is warmer, thicker, and has more body; with upper mids U4-SE is brighter and more revealing while Pro50 is smoother, warmer, and more laidback. Treble is very similar in both, though I hear just a little more sparkle in U4-SE.

U4-SE vs U6

Conclusion.

I often hear after my reviews: there is no “clear winner” from comparison and pair-up sections. And my response is always the same – the intent of my write-ups is not to give you Top5 with a clear winner and everything else ranked down to the last place. For me, writing a review is the way of describing how I hear audio gear and how it compares relative to others. We all have a different sound preference, use different audio sources, and have a different sensitivity to frequencies across FR spectrum. So, for example, as much as I think U6 is a great pair of IEMs, for me personally I found U4-SE to have a more balanced and revealing tuning which sounds better and hits closer to my sound preference. But this is my own personal preference, and as a reader you have to decide which one is your cup of tea.

Because it’s a Special Edition version, the availability of U4-SE model is limited. I have seen it being offered once on MassDrop, and as part of 64 Audio B-stock sales, and currently on Summer Clearance Sale. I don’t know how often these go on sale and if 64 Audio will continue to make more U4-SE in limited production batches. But if you ever been curious about 64 Audio and their Apex modules and if you fancy a balanced tuned IEM signature with an excellent low end impact and revealing/transparent upper mids with a nice treble sparkle, give U4-SE a serious consideration, especially if you are on a budget.

 

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37 thoughts on “64 Audio U4-SE”

    1. I never heard the original u4, but others mentioned it has a rather basshead oriented tuning – more emphasis on low end and rolled off upper frequencies. Again, never heard these so can’t say for sure, but sounds like a different tuning in comparison to SE version.

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  2. My question is not directly related to U4SE. I saw you mentioned UM Pro 50. Can you please briefly compare UM Pro 50 to iBasso IT03? Are they similar or completely different in sound signature? I own UM Pro 50 (upgraded from UM3X) and planning to get iBasso DX200 soon. What, in your opinion, would be a step up from UM Pro 50 to pair with iBasso DX200, considering that I like UM Pro 50 signature? Thank you!

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    1. Something like it03 or u4se will be a side grade rather than upgrade from umpro50. Westone has this unique signature where the sound is less aggressive, more laid back. Going to it03 will make sound more v-shaped, where stepping up to u4se will be an upgrade from it03. U6 has a similar less aggressive tonality, but going from umpro50 to u6 will mean sacrificing bass and smoothing out top end. Look into mine w80 review, in my comparison between w60, w80,es60, umpro50 – it can give you a good idea of how these Westone iems stack up against each other. Also, keep in mind, it04 is around the corner.

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    1. I have been told it could go on sale toward the end of this week. This is a limited special edition. They don’t sell it regularly. Yeah, curious how it04 will sound as well.

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  4. I purchased these recently as B-stock, right before the summer sale (doh!). Although sometimes the bass is strong, with most music I can’t hear it very well. Sometimes certain notes seem to be quieter than others to the point of not being able to discern the pitch of the note or that there’s a note played at all. This is compared with any other headphones I own (Q701, ATH-M50, ATH-IM70, MDR-7506). I prefer to listen on any of these, due to oI don’t have extensive experience with any other higher-end IEMs. Based on your experience, does this sound like an issue with the tips and the fit in my ear, a RMA issue or just a mismatched expectation for what IEMs can do? Most friends who have listened to these, though not all, have complained about bass response. Unfortunately I can’t return them in any case, as I purchased B-stock.

    Thanks much

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    1. I think it’s a combination of both, perhaps not a good match with a current set of eartips where you are not getting a good seal, and also a different expectation and sound preference where you comparing it to heavier bass full size headphones. The original U4 as well as higher end U8 are for basshead lover, that’s probably where you threshold of bass preference is. U4-SE is a totally different beast, re-tuned and redesigned for audiophiles, different grouping of drivers going to the nozzle bores, different tuning, etc. These are going to be bass-light and intentionally tuned for that purpose because audiophiles want a more balanced sound. For me personally, they have plenty of bass, but it will vary from person to person, due to our sound preference. The supplied eartips are not that great, you need something firmer.

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  5. Trying to decide between these or CA Lyra II. Both used. This being a bit cheaper. Used with Opus #1. Current top IEM is the AKG N40. Haven’t heard a BA only IEM.

    I like a present top end but am sensitive to sibilance and too much in your face treble

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    1. Sorry, not familiar with Lyra II or N40. U4-SE shouldn’t have too much “in-your-face” upper mids/lower treble. It’s not exactly laidback/smooth, but I don’t consider it to be fatigue.

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  6. Thanks for this review man
    I’ve searching for a good mid-tier IEM for my AK70 (very difficult to match DAP) , i tried the Dunu DN-2002 wich are very good match, but are very uncomfortable too…
    i sell my Westone W40 because his laid back signature does not match with the warm coloration of the AK70
    Then i read this review, and i want to try the apex modules in a mid-tier iem without lose too much money…
    Well i don’t lose my money, this IEMs have all the advantages of the W40s, same retrieval of details, a bit more bass tuned and less laid back signature, very balanced IEMs perfect for warm sources, very comfortable to wear and don’t cause fatigue…
    Very good review, this IEMs are exactly as you described it

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  7. Nice review. Interesting because of the massdrop 😉
    how would you compare the u4-se with the flc8 or custom art ei.xxx ?
    Thanks

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    1. well, FLC8 gives you a lot of flexibility to fine tune the sound because of all the filters, but it can’t match the impact and articulation of U4-SE bass, and also FLC8 doesn’t have the same level of transparency and detail retrieval… Ei.xx is ok, but too smooth and laidback in comparison, not anywhere close when it comes t layering/separaiton/transparency and detail retrieval of U4-SE. It has been awhile since a sub $1k iem impressed me that much, though I also like IT03 3way hybrid, but when it’s paired up with their CB13 cable, which both cost as much as U4-SE.

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  8. Nice review. Trying to decide between the u6 and u8
    My current iem is um pro 50,and I love rock n’ roll so I prefer bass.
    But I kinda feel like pro50 sound really thick ,warm and the bass just overpower the mid and high.
    Ive demoed the A3 once only remember is clear and tight.
    Looking for smooth, neutral, clear , detail, fast and crisp bass sound.
    Need some advices ty.

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    1. U6 might be too neutral for your taste. I didn’t hear U8 but it’s considered to be the basshead of the family 🙂 It probably will satisfy your bass needs but I’m not sure if it will overpower mids/highs. U4SE will give you a good doze of bass and crisp mids/treble for the guitar crunch. I have umpro50 and u6, but personally will choose u4se over them.

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      1. Thanks dude. after I demoed some high end IEMs
        I prolly will get U12 over s-em9,Andromeda,JH13,Katana
        Should I get the old ADEL model or the new APEX?
        The 64 Audio ADEL model is on sale on my local store.

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  9. Great review! Of particular interest is your comparison between the U4SE and U6. I listen to mostly indie rock with predominantly male vocals and prefer a fuller vocal rather than one that can be described as thin or noticeably recessed in the mix. Could you please elaborate on your statement “U6 lower mids are warmer and with a little more body, while U4-SE lower mids are leaner and cleaner”? If I am not mistaken, male vocals typically fall within the lower mids so I am slightly concerned about the U4SE’s presentation in this area. I typically listen at lower volumes as well, so don’t want to find myself listening too loud to bring the vocals up. I am just trying to determine if the extra cost for U6 is warranted. Thanks for your time!

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    1. Based on your requirements with emphasis on vocals, i do believe you will benefit more from U6 tuning. U4SE is for more revealing, maybe even closer to analytical audiophile listening, for sure the sound is crisper and more revealing when compared to U6. Especially for a fuller vocal range, U6 will suite you better.

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      1. Thanks for the quick response! Your thoughts confirmed my suspicions. What do you make of the impedance adapter talk regarding the U6 and U12’s? I read that a 20 ohm or even 75 ohm adapter is needed for the U6 to sound its best due to it being mixed for pro audio use? I’ve also heard that these adapters actually degrade the sound quality? I’m a bit confused about this and honestly one of the reasons why I was thinking about just getting the U4SE.

        I forgot to mention I am also sensitive to peaky treble and sibilance. I assume the U6 would be better as far as that goes and be less fatiguing?

        Thanks so much!

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      2. Yes, U6 will be less fatigue. With U6, according to 64 Audio rep in head-fi thread, those were tuned for performing musicians who use wireless packs that have higher output impedance. U4-SE was tuned for a typical DAP/smartphone application with a lower output impedance, the same as their flagship U18/Fourte. Don’t use impedance adapters, instead try it with UE Buffer Jack (only $10), imho works better 😉

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  10. Thanks! I think I’ve decided on the U6. However, I was planning to use them balanced and can’t seem to find anyone selling a buffer jack or impedance adapter for use with 2.5 mm balanced cables. So it looks like my options are to run single ended with the buffer jack OR go balanced and live with the lower output impedance of my xdp-300r. I could even run balanced and apply a bit of EQ to boost the upper mids slightly as recommended by Brooko. Have you tried any of the 64 Audio iem’s balanced?

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    1. I use U18 and TIA Fourte balanced only because those are resolving iems that benefit from high end sources that have balanced outputs with a black background. Don’t think U6 will benefit from balanced of 300r, cause i was under impression these onkyo/pioneer daps only boost the power in balanced, not the actual audio performance. Either way, don’t get too overwhelmed with bal vs se. Since i assume you have 2.5mm terminated 2pin, just try it to see if you even hear any difference. Listen to your ears 😉

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      1. Listen to my ears… why didn’t I think of that! I’ll just wait and see how I like them first and go from there. Thanks again for your insight!

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    1. They are on a thinner side, but still build tough. Plus, if anything, 64audio will replace it under warranty. If you are on a budget, you can get pure copper cable from Penon, check out my review from a month or two ago. Effect Audio makes very good cables, but pure copper will run you $150. Still a bargain in comparison to some of the $1.5k-$2k cables i’m using lol!

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  12. Hi, I have U4SE in my possesion and I’m in the market for Android DAP. I’m new to this DAP thing with my most recent experience is with fiio X3iii. Do you think HiBy R6 will be a good match to U4SE? I’m a little bit worry of the high OI of R6, maybe you can test them out? I also consider Cayin N5ii if R6 just alters the sound signature of U4SE too much.
    Also I’m thinking about purchasing Focal Clear soon so I need a DAP that can handle both U4SE and Clear.
    Thank you for your thought.

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    1. I haven’t ried U4SE with R6, but I’m pretty sure it will change the sound, but not a problem if you use iEMatch from iFi, it will “restore” it back. Are you in a market for Android dap to run apps and streaming and bluetooth headphones? If you want the best Android experience, get R6 with iEMatch impedance adapter. Otherwise, if you want a good audio “budget” player and just occassional streaming (like Spotify or Tidal) N5ii is really good actually. In theory N5ii and R6 sound very close, just with multi-BAs that use crossover, you will need iEMatch or Earbuddy from iFi when using R6. Focal Clear should sound the same with both N5ii and R6… Btw, I will be working on N5ii review next and then R6.

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      1. cool. could you please use U4SE or other multi-BAs IEMs in your R6 review later so we can see how big the impact? looking forward to read your review! *and then I’ll decide

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      2. output impedance of R6 has zero effect on U4SE, it sounds identical with and without iEMatch. U4SE was tuned and designed for higher impedance output sources.

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      3. thank you! I’m glad to hear that U4SE sound is not changed by R6 despite having impedance as low as 12 ohm. now I can back the R6 campaign with confidence.

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    1. This is not U4s model they are currently selling. U4-SE (U4 Special Edition) was a very old 7+ short-lived model they made for crowdfunding sale, prior to them refreshing their whole product lineup with “tia” models. This review is just a “time capsule” from the past, and unfortunately it pops up in Google search whenever someone is looking for new U4s 🙂

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