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Geometric Brass Design – Acoustune HS1650CU Review

Geometric Brass Design – Acoustune HS1650CU Review

Acoustune HS1650CU is the first IEM I am reviewing from Acoustune, a special Brass chamber, single Dynamic Driver IEM, with a very unique geometric and aesthetic approach. They are priced at 650 USD and my review will be focused on assessing their performance relative to their price. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven



Acoustune is a large company from Japan, with all their products made and assembled in Japan, so you can expect a truly impressive Japanese quality of them. They have a true quality not only to their final product, but also to their customer service, the accessories their IEMs come with, and to the overall Acoustune experience. 

It should be noted that I have absolutely no affiliation with Acoustune, I am not receiving any incentive for this review or to sweeten things out. This review is not sponsored nor has been paid for by Acoustune or anyone else. I’d like to thank Acoustune for providing the sample for this review. The sample was provided along with Acoustune’s request for an honest and unbiased review. This review reflects my personal subjective experience with Acoustune HS1650CU. Every opinion expressed is mine and I stand by it, the purpose of this review is to help those interested in Acoustune HS1650CU find their next music companion. 


Product Link

You can purchase from www.amazon.com here: https://amzn.to/3qLv4Xj



This time I can brag about the package, because Acoustune HS1650CU really comes in a sweet little package! Let’s just say it is not only sweet, but they have a better package than most flagships I review, some of them even considerably more expensive. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

Starting with the main package, Acoustune HS1650CU comes in a larger cardboard box, inside which there is another cardboard box. Inside that, you can find a fully metallic carrying case. 

Acoustune HS1650CU is seated very comfortably inside a foam cutout, and they come with a large number of handy accessories, like a leather / leatherette carrying case, a large selection of tips, and an ultra high-quality, silver plated, Oxygen-Free Copper Single Ended Cable. 

The cable has a 3.5mm gold plated jack. 

Everything is absolutely outstanding with their package, and HS1650CU reaches my golden standard easily in terms of packaging. 


Technical Specifications

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

Build Quality/Aesthetics/Fit/Comfort

Okay, so this is one of the most beautifully built IEMs I’ve seen in a long while, and also quite similar to IMR R1 Zenith in terms of overall shape, but still Acoustune HS1650CU is a thing of its own. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

The IEM is fully made of metal, with a beautiful overall design, and with excellent ergonomics. There is a little part towards the back inner part that may touch the ear and cause discomfort for those with smaller ears. This being said, the comfort is mostly okay for most people. 

The cable wraps around the ear, and they are supposed to be worn that way. This means that there are no cable microphonics, and the comfort is pretty excellent. Acoustune HS1650CU isolates fairly well from the outside noise, and they tend to be very good at feeling open. There is no driver flex, and quite honestly, they feel good while being worn. 

The cable is actually a very high-quality braided cable that is very tangle-free, made from Silver Plated Oxygen-Free Copper. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

Overall, the design of Acoustune HS1650CU is simply beautiful, they have a really unique shape, and from their own words, it looks like the inner chamber has a lot to do with this. The matte black with gold accents truly shines a new light on how to combine elegance with expressivism, strong rich accents with a smooth background, making Acoustune HS1650CU really stand out from the Mass of IEMs I’ve been reviewing, and giving them a cool edge, and this time not for an edgy look, but for a very stylish and clean aesthetic. The fine work of Japan’s best is easy to see, as there is an excellent attention to detail, and every single surface is worked with care, cleaned, and polished, making the entire IEM look even better than a luxury watch. 

Happily, on the inside, there are L and R Markings, along with color coding of rings along the MMCX connectors, so you don’t have to worry which is the left and which is the right IEM. The cable also has L and R Markings. 

The cables do not have ear guides, and are soft when they go around the ears, which helps a lot with the overall comfort. The cable is ended with a 3.5mm Single Ended Jack, and with a larger stress relief. 

There is a good selection of tips included in the package, including double flanged tips and foam tips. 

Overall, the build quality, aesthetics and comfort are pretty much golden, the IEMs look beautiful, they fit beautifully, and they feel very comfortable while in usage. 

Sound Quality

Before I drive in the sonic department, Acoustune HS1650CU is a Single Dynamic Driver IEM, and they have all the inherent advantages of this, including an excellent coherency, and a perfect phase, but furthermore, the driver is made using a very thin and light membrane. 

The sound could be described as Full, Dynamic, Punchy, Deep, Impactful, Meaty, Intimate, Wide, Emotional, Detailed, Clear, Clean, Fun, Tactile, and Engaging. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

The bass has an excellent extension in the sub-bass, and the quantity of the sub-bass is very satisfying, aiming HS1650CU at a crowd that prefers a warmer and meatier sound rather than a fully neutral sound. The rumble is all there, and there are no distortions, making listening to HS1650CU pretty enjoyable, even at ear-bleeding levels, but also at very quiet levels. The bass decay is on the quicker side, indicating a fast speed for the bass, and they can keep up even with the most aggressive of Technical Death Metals, or complex Electronic like Infected Mushroom, without feeling like they’re struggling. The bass texture tends to be a touch more creamy in contrast to its quicker speed, and the mid-bass isn’t enhanced quite as much, leading to an agile overall sound, although the impact is very impressive. 

The Midrange sounds a touch more lively and open, although the textures have a leaner presentation. The transparency is very good, and HS1650CU feels quite revealing, although the lower mids are lesser in amount compared to the upper midrange, resulting in a more intimacy with female vocals than with male vocals. This being said, HS1650CU doesn’t have any kind of issue to present even low baritone male vocals, and they go an absolutely outstanding and beautiful job with guitar solos, even the most aggressive of metals having a juicy and fun presentation. Furthermore, when listening to some sweet female voices, you get goosebumps all over your skin, and shivers, from the way HS1650CU manages to present them so close to you, so natural, and so realistic. 

The treble has an excellent extension and air, but it isn’t quite as enhanced in the upper treble, as it is in the lower treble. The lower treble bump gives them a good amount of detail, but there’s no harshness, the treble having a smoother texture, and there is no sibilance, the bump in the lower treble being moderate enough so it doesn’t lead to any kind of harshness. The treble could be said to have enough sparkle to liven up the entire sound, and there are no odd resonances at any point in the sound. 

The whole sound is very crisp and well-defined, and well-controlled, HS1650CU being a very authoritative IEM with a punchy, yet really well-controlled sound. They make one of my favorite 700 USD IEMs, in terms of sound alone, and the first time I plugged them in, I felt like “that’s good, I just need more of this”, at the end of the day, listening to HS1650CU for more than three hours straight, simply listening and not analysing, as those aren’t analytical headphones, but very analogue-sounding ones. 

The Soundstage size is fairly natural, the width and depth are both equal, creating a good amount of space around the listener. Combined with a pretty darn impressive instrument separation, and a pretty accurate positioning and stereo imaging, HS1650CU is an incredibly enjoyable experience. 

Portable Usage

The portable usage is pretty much excellent.

HS1650CU is a pretty light IEM, with a good amount of power, they are easy to drive but also scale with a good source. They isolate pretty darn well from the outside noise, so please pay attention, so you don’t find yourself dancing inside a store, because the tune was just that good. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven


They have a tendency to sound meaty and full, giving the sensation of real music, even while on-the-go, and a slightly enhanced bass and more meatier sound are preferable for outdoors usage, as usually the sound of walking tends to drown out some of the bass in music. The same can be said about the treble, and happily, HS1650CU delivers there as well, the slightly V-shaped signature managing to get through the noise of outdoor usage quite well. 

HS1650CU doesn’t have a perfect noise isolation, I’d say they have about -15 dB of isolation, which means that you can use them freely while walking without being afraid that you won’t hear a true danger, like a dangerous dog barking, or a car’s horn. 

The leakage is minimal to absent, which means that you could go inside a library and blast some metal without anyone there noticing. 

The cables are a touch thick and heavy for walking and running, but they are within comfortable limits, while the microphonic noise is non-existing thanks to the over-the-ear design. If you manage to wear them straight-down, they still are microphonic noise free, because the cable just isn’t all that noisy, and with a tangle-free cable, they are surely going to be easy to take in and out while out and about. 

Overall, they are very portable and very enjoyable on-the-go, just like HIFIMAN RE800 Silver whcih barely touches the ears while being worn. 


Acoustune HS 1650 CU has a lot of enemies in the same price range, but they also make a good call, being made of metal, being designed and crafted in Japan, which is a true heaven, and for having a really amazing and detailed sound for this price range. 


Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

Acoustune HS 1650 CU vs Beyerdynamic Xelento Beyerdynamic Xelento is still a very popular IEM for those who are looking for a really smooth and thick IEM, with a really strong sub-bass and bass, a really thick and smooth midrange, and an extremely smooth treble. The package is similar between the two IEMs, and they both come with similar accessories, but it should be noted that Acoustune HS 1650 CU uses universal tips, while Xelento has its own tip mechanism and you need to rely on the tips included in the package. The comfort is good on both, but Xelento is more of an superficial / Shallow fit IEM, while Acoustune HS 1650 CU has a more typical normal depth fit. Xelento has a bit of driver flex, while Acoustune HS 1650 CU has none. The sound is similar, yet quite different. In raw details, they are similar, but Acoustune HS 1650 CU feels more transparent, and shows more textures and micro-details than Xelento, which instead takes the path for a much smoother and cleaner sound, deeper and creamier, with less emphasis on the treble and the midrange, and with a larger bass. Acoustune HS 1650 CU goes for a more natural and less creamy presentation, for a more natural overall texture presentation. The soundstage is huge on both, but I’d give the size prize to Xelento, although Acoustune HS 1650 CU does have at least as good imaging, if not even better. Overall, if you’re looking for a really creamy, thick, bassy, warm and smooth sound, Xelento is more suited, while if you’re looking for a really natural IEM, with a warm and thick sound, yet with great details and clarity, Acoustune HS 1650 CU makes a very compelling option. 

Acoustune HS 1650 CU vs Campfire AtlasAtlas is a really interesting IEM because many are in love with it, and for a good reason, Atlas is one of the flagships from Campfire, a really loved company from USA. This being said, Acoustune HS 1650 CU is made in Japan, and doesn’t take a step down, having a really amazing package, with at least an interesting carrying case. Atlas comes with a more premium carrying case, and more tips, but this is to be expected, considering that Atlas costs about double the price of Acoustune HS 1650 CU. In comfort, I’d say they are really similar, if anything, Atlas is a little held down because it has driver flex for some users, although if you’re really slow and careful with them, I noticed that I didn’t get almost any driver flex. On the other hand, Acoustune HS 1650 CU seems to fit pretty much perfectly for all users. The sound is larger, and more grand on Atlas, with more of a peak in the midrange, which may seem a bit unintuitive, since they are always called as being warmer and bassier, but this is because the peak in the upper midrange / lower treble compliments the large bass, to give them both a grand, explosive and yet balanced V-shaped signature. Compared directly, Acoustune HS 1650 CU sounds a bit less grand, but more precise, the impact isn’t quite as ferocious as it is on Atlas, but it has more precision, cutting like a Japanese sword. Furthermore, if you’re sensitive to upper midrange / lower treble peaks, Acoustune HS 1650 CU doesn’t use them, instead being quite even in that area, relying on a more forward overall midrange, and just a more balanced overall tuning, closer to being linear, to sound natural. The two are different, and I’d say complementary, if you’re looking for a really large-sounding, grand, impressive, deep and warm IEM, that still holds a fine sparkle in the treble, Atlas still makes a really compelling choice, while if you’re looking for something a touch smoother, less large, but more precise, with more agility, and with a more linear signature (in comparison), then Acoustune HS 1650 CU makes a really good offer, especially since it is about half the price of Atlas. 

Acoustune HS 1650 CU vs Dita Answer Truth EditionDita Truth is actually interesting, because it is pretty much the same price as Acoustune HS 1650 CU, but it has a really really different sound. The package is excellent on both, and both are really comfortable, but Dita Truth has no detachable cables, instead using the Van Den Hul cables they sport to paint a truly amazing image. Furthermore, Dita Truth is focused way more on a really analytical, bright, precise, tight, and sparkly sound, Acoustune HS 1650 CU sounding much thicker, more bassy, slower and less airy. Dita Truth is like a precision surgery knife that shows you details you didn’t know existed, but that blade has two edges, because you may not always want that kind of precise painting, and instead would want to sacrifice some speed and detail for a more romantic and natural painting, like the one Acoustune HS 1650 CU paints. If you’re looking for a really precise IEM, with a lot of detail, a wide soundstage, and an excellent comfort, being powered by Van Den Hul cables, then Dita Truth is still a favorite of mine, while if you’re looking for a more natural, thicker, slower, yet more romantic, experience that makes you forget about the listening, ang switches your focus on music instead, then Acoustune HS 1650 CU makes a really nice offer. 

Recommended Pairings

Acoustune HS1650CU tends to pick up some hiss from hissy sources, but they aren’t quite as sensitive to hiss as other options, yet this may be noticeable, so hissy sources like Hiby R6 should be avoided. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

Acoustune HS 1650 CU + iFi xDSD DAC/AMPiFi’x xDSD is still one of the DAC/AMPs I can recommend the easiest, especially when you look at the features it has, like the X-Bass and the 3D soundstage, along with Bluetooth and even MQA decoding abilities, making it one of the most ideal solutions if you prefer using your smartphone as a transport, and using an external DAC/AMP for sound. The pairing with Acoustune HS 1650 CU is quite ideal, as xDSD is a fairly neutral, sweet, and wide-sounding DAC/AMP, and if you want to add a touch of further width to your stage, it is right there, at the touch of a button. There is no hiss with this pairing.

Acoustune HS 1650 CU + FiiO X7mkii FiiO’s X7mkii is still very relevant, and one of the most widely used Players among music lovers all around the world, and for a good reason. It has a very vivid and detailed sound, access to wifi, streaming services, and two microSD slots, along with other features that you’d totally enjoy. Paired with Acoustune HS 1650 CU, you get a deep and punchy sound, but X7mkii’s quicker speed also makes Acoustune HS 1650 CU a touch quicker, giving them a more precise hit, although they were already quite precise to begin with. The really wide presentation also compliments Acoustune HS 1650 CU well. There is no hiss with this pairing.

Acoustune HS 1650 CU + iBasso DX200 (AMP5) – DX200 and AMP5 are a combo that can not only drive Acoustune HS 1650 CU well, but they can also give them amazing dynamics and punchiness. To add to the mix, DX200 is one of the widest DAPs I heard, and this transfer to Acoustune HS 1650 CU, making them wide and holographic. You also get the latest Android updates, along with streaming services support when going with this combo. There is no hiss with this pairing.

Value and Conclusion

It has been truly fun to review Acoustune HS1650 CU, and I’m sure it will remain in my heart for a long time as one of the most enjoyable IEMs I tested to date. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

To be fair, it isn’t even a IEM I’d consider to be an experience, more than just an In-Ear, because the first thing I did when I plugged it in, was to listen to music, rather than to analyse how it sounds. The naturalness of the sound and the comfort made me think of music first, and second of what I was using to play it. And I think this is pretty much where all audio-related products should be, enjoyment pieces that make us forget about them as audio products, and think more of music. 

The build quality is amazing, but even before getting to the build quality, you’re greeted by the finest work of the Japanese Company Acoustune, and their Made In Japan IEMs, HS 1650 CU, in the package, which is not just purely amazing, but also includes things in a new manner, if you’re used to IEMs. You get a metallic case, that you could always use to carry your IEMs and a DAP. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

You also get Acoustune’s amazing cables with their IEMs, and as far as I know, this costs quite a lot when sold separately, and is held in high regards by cable experts. 

The comfort is quite excellent, they go naturally around your ears, there’s no driver flex and no cable microphonics, Acoustune HS 1650 CU is simply too comfortable to be called a typical IEM. The excellent tips included in the package also help with this. 

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

Overall, the sound is quite natural, meaty, thick, punchy, deep, dynamic and fun to listen to. The upper midrange has a small bump that makes female singers come a touch closer than male vocals, giving them an interesting edge for ACG music, basically Japanese music – which I happen to enjoy quite a lot. This being said, and HS1650CU is very versatile, working well with Classical, Metal and even complex Post-Hardcore music. Electronic music is also one of their strengths, and so is pop, making them a truly good-for-all IEM.

Acoustune HS1650CU Dynamic Driver IEMs Review Audiophile-Heaven

At the end of the day, if you’re looking for a warm, thicker, fun, natural, smooth, punchy and dynamic IEM, priced at about 650 USD, with an excellent comfort, with amazing levels of details, and with an overall tuning and comfort that can be only described as “it makes you forget about the IEM, and it makes you focus on the music”, then you should totally check out Acoustune HS 1650 CU! 


Product Link

You can purchase from www.amazon.com here: https://amzn.to/3qLv4Xj

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Full Playlist used for this review

We listened to more songs than those named in this playlist, but those are excellent for identifying a sonic signature.  I recommend trying most of the songs from this playlist, especially if you’re searching for new music! The playlists are different for Spotify, Tidal and Youtube, and based on the songs I enjoy and are available on each!




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