Introduction

The EST50 focuses on whats most important, musicality. Its simply a love letter to music. The organic, meaty playback combined with EST goodness creates one hell of a perfect tuning. While these may not be for everyone, when they hit you there is no going back. Its hard to imagine anything better when it comes to providing this kind of signature. ISN really outdid themselves here and you get a true flagship

Everything you listen to just pulls you into the experience. Thick juicy mids with a slight warmth to them, crispy highs that give you all the micro-details you could ever want for casual listening. And then there is the bass. So tastefully elevated that you could even trick your brain into thinking the EST 50 sounds natural – but make no mistakes. The low end is bold, reaches deep and when called for, transports you into another realm of existence. When that bass hits, the “Trinity of Forces” is combined, fully pulling you into the universe of sound

ISN manged the impossible here: They created a fun, at times even bass-head level IEM and tuned it to perfection. This is not your typical “bass over everything” one trick pony. It does it all. And in the right manner. There is nothing missing. I can nitpick them for having bass that's slightly on the lower side but with 90% of my library they play effortlessly and make up for in texture and extension


A word on burn-in: I liked them from the moment I put them into my ears and have been listening to them nonstop ever since (probably 200-300 hours in under a month). If they changed, maybe the bass tightened up a bit and the upper region lost a tiny bit of edge but it could also simply be fit or “brain burn-in”. What I can say is that they are considerably brighter than I expected, which in part has to do with my tips of choice (Clarion Tri). With stock tips they could at times become a bit too warm/bassy for my liking



My background

I always tried to get the best sound my limited money could buy back then and my first headphones where the Audio-Technica ATH-50. They served me well for years. Not perfect by any means but still a good and honest pair of headphones that sounded pretty nice considering the price. Then I bought my first home stereo, which I still have to this day. Nubert Nubox 381 and a AW-560 subwoofer with an Onkyo amplifier. The system sounds nice and was my “benchmark” for a while

Then I got my first IEM: the Phonak PFE112. For around 130€ you got something that redefined the price bracket back then, at least according to head-fi and reviewers… So I bought them and immediately fell in love. 1 BA was able to provide amazing details, great treble extension, nice mids, the bass was lacking but they still wowed me with overall sound and comfort. There was also the much more expensive model, the PFE232. A jump from 130€ to around 450-550€. I kept reading reviews and couldn’t resist when they were on sale for 250€ (they were a few years old but still highly regarded in the audiophile world). A big step up from the 112 for me, trading flat for a v-shaped tuning that was tastefully done. The bass was great for BA standards and they immediately became my new “benchmark” for sound. It was almost perfect, although sometimes I wanted a bit more bass

A few years later my last working cable (proprietary connector) failed and only the right side is still working. I could have got a new cable for 130€, which was only 10€ less than the LETSHUOER S12 Pro, so I went for that since it had good reviews and a few people said planars are the logical step up from the 232 because of the detail retrieval and speed. Liked them but they had a few problems which I will be going into later. After a lot of research I stumbled upon the EST50 by accident and bought them after some consideration



Build/Appearance and Accessories

They are stunning visually (I got the green version) and build very well. Being able to look inside just adds to the excitement when you first receive them. The connector is pretty tight, which helps the cable to stay in place. Compared to the connector on my S12 Pro, which is looser and the cable can come out a bit after time. Overall I feel confident that they will last a while, with proper care of course

Accessories are on the sparse side. Its fine, they focused their money on the product and at least you get a nice case with it. The included cable is great when it comes to comfort, micro phonics and I like the overall sound it gives



Fit and pressure build up

Considering how big they are, the fit is pretty nice. Comfort wise they are above average, even great with the right tips. I can wear these for hours without any major problems and they adapt perfectly to the shape of my ear. They are also leagues more comfortable than the S12 Pro for me. The first problem is the ear hook on the cable, which just violates my ears after a while. This is fixable but still annoying cause I kinda like the cable it came with. The second issue is the major one though and can’t be fixed:

The S12 Pro has no proper pressure vent. This means that my ears start hurting after a while if the bass is present in a level I enjoy and I can’t listen to loud volumes because the amount of air they push hurts my ears. The EST50 has pressure vents, at least I think that's what the tiny holes on the side are. And they to a fantastic job. Not only can I listen over long periods without annoyance/pain, I can also listen at louder volumes without any fatigue



Tip synergy

Included Tips (Green) → While they offer a nice sound with elevated bass, they are simply too big for my ears which makes them rather uncomfortable after a while. Also they can make the sound a bit too warm on some tracks for me

Spinfit CP145 → Pretty comfy but sound wise they are not my favorites

White Tips from S12 Pro → The sound with these tips is nice. Strong bass, highs still come through nicely while reducing the sibilance. Sadly another pair that violates my ears after a while

Spinfit W1 → These were my favorites since I got the EST50. Not perfect in terms of comfort but I very much liked what they did to the sound. Bass is more controlled without losing impact, sound stage an imaging feel slightly improved. The problem is, they can lose seal for me after a while and I decided its not worth the hassle after they got stuck in my left ear 3 times on a single day when trying to take them out

Clarion Tri Tips → Got these after a recommendation from a fellow head-fier. These give you all the benefits of the W1 and more. They are more comfy, so comfy indeed I forget the EST50 are in my ears. They sound similar but also improve on certain aspects. With the W1 you get a bigger stage but it feels slightly artificial. Everything is pushed to the side but you gain nothing in terms of depth, which makes it sound a tad unnatural. The Clarion Tri doesn't do this. The stage is improved slightly but more importantly the imaging and 3d-ness improves. It sounds very natural this way . Bass is not muted at all, its as tight and as defined as with the W1. The only “slight” con to these tips is that they can sound a bit sibilant on some tracks. I already gotten used to it after 3 days and the pros far outshine the negatives for me. Right now these are definitely my favorites with the EST50 but I will try the Penon Liqueur soon and edit this review accordingly



Source

I use these almost exclusively with my Hiby R5 ii. I also tried them with a usb-dongle from ISN and my Ifi-Hip Dac. They definitely benefit from a great source. The difference from the usb-dongle to the Hiby is rather big and noticeable. With the dongle they sound fine but a bit flat and boring. Its just like the soul has been sucked out a bit. Similar (although better) results with using the Hiby without class-a engaged. As soon as you hit that switch and the class-a amplification is turned on you immediately notice the difference. The clinical sound is gone. Bass has more impact, the overall sound is more organic/slightly warm and note weight is greatly increased. Its a rather stunning pairing. Imaging and stage are also slightly improved

With the Hip-Dac they sound nice indeed but there is a rather noticeable noise floor when nothing is playing and on quiet passages. At first I thought my Hip-Dac is broken but the EST50 is just a good amount more sensitive when it comes to noise floor than the S12 Pro. I even notice a slight noise floor on the Hiby R5 ii but its nothing compared to the Hip-Dac

That being said, the sound with Hip-Dac is better than I expected. Its not as refined as the Hiby but the bass is a bit more pronounced (texture, definition and control are all better on the Hiby though). Its not even overly warm with most tracks but can definitely verge a bit on being too warm on some tracks. You get zero sibilance in return though, so its definitely a trade off. If I am in the mood for a bit more bass and warmth in trade of better technicalities I reach for the Hip-Dac. Overall I enjoy what the Hiby brings to the table more as it finds a better balance between sounding organic and detailed. That being said if you are looking for that “brickwall” type of sound (especially with rock/metal), the Hip-Dac got you covered

The EST50 scales very well and I highly recommend to use a quality source for them!


Sound

Bass

The bass of the EST50 is something special. It reaches deep, has impact and is still rather controlled considering how much its boosted on some tracks. It can struggle with faster passages and may sound a bit loose sometimes but you get musicality and texture in return. It has the ability to produce a subwoofer-like experience, which is especially great with movies. For music it adapts greatly to source material. These IEMs can go from sounding very neutral and true to life to an absolute brick-wall of sound. When bass is dialed back or there is not much sub-bass in the track, the EST50 provides you a clean, neutral and very hifi-sound. You wouldn’t even get the idea these could reach bass-head levels with certain songs. But the fun factor is still fully there, it sounds musical, engaging and very airy. Its just a different flavor.

When that bass hits though, the sound interestingly doesn’t lose much in terms of clarity. Its rather a miracle how the EST50 is able to provide this amount of bass while still giving the other frequencies room to breathe. Part of that is that the mid-bass is tuned rather neutral with a strong boost in the sub-bass region. This results in a pretty versatile IEM, that will only deliver what the source material provides. This makes it especially engaging with energetic music like Rock, Metal and Electronica. But acoustic music is also a real treat. Instruments have great definition and body to them, ranging from sounding very clean or warm depending on the track. Acoustic bass sounds amazing on these and provides a nice groove to the song. The amount, at times verging on being too much, still manages to mostly strike the perfect balance between providing the most amount of bass possible without cannibalizing the other frequencies. Texture is well defined, it reaches very low and is overall a pretty versatile bass that provides almost always. Overall the best bass I heard in an IEM and while I wish it would be a bit tighter and more controlled at times, the musicality it provides makes me forget these shortcomings

Mid

The mids on the EST50 integrate well into the rest. Vocals mostly sound natural with a great sense of air around the artists and while dialed back a tiny bit, you never lose clarity or presence in the vocals. I actually like this very much, since it provides you with a non-fatiguing but highly resolving playback that still does the performers justice. Vocals "can" sound lovely on the EST50, clean, well textured and natural. They are just not put into the center of the stage and it depends on how the track was mixed.

Instruments also shine. Great sense of air, gives a very true to life playback of instruments. The mid-range can at times provide you a nice warmth which makes the signature even more organic, again it is track dependent though. On most Rock/Metal songs it adds a lot of excitement. They are never overly warm and provide great details and texture. Versatile mid-range that plays everything without a problem. Its highly resolving (if you listen for it) but never demands to be in the center of your attention

Treble

These are my first IEMs with EST drivers and I am rather impressed. I immediately noticed the incredible amount of air they are able to provide. It gives the signature a nice edge, that is very detailed and can be sparkly if the track calls for it. It manages to provide all of this without a hint of sibilance (depending on the tip). These are by far the best highs I have heard so far, even trumping my beloved PFE 232 by a good margin (the highs where pretty outstanding on them considering the time they released and are still no slouch by todays standards!). These are not “dark” in the slightest, at least with the right tips. Absolutely love the highs. Effortless and smooth, while still giving you enough information!


Sound stage

The sound stage offers decent width but is rather shallow in depth. It feels like the artists play inside your head – everything is more intimate but with that comes excellent imaging and it can appear very 3d like depending on the source material. Even when it comes to width its nothing outstanding but its perfectly serviceable and allows every element to “live in its own space”



Music


Electronica

Sensitive – Jean du Voyage

The EST50 strikes a perfect balance between tight drums, a gorgeous sub bass and 3D imaging

The moment you hit play, you immediately know where the journey is going. The main synth has a rather nice low end to it. Very organic pad sound. Then the drums come alive. Very lifelike and a bit in your face, the drums demand your attention. When the kick hits, the real journey begins. Deep fat bass that harmonically integrates so well with the rest. The reverb on the drums sounds very realistic and you can hear all the tiny nuances in the decay. Nice sense of space with good imaging. The lead synth goes along with the groove. The higher synth has a nice presence and movement to it. Very crisp and detailed. The kick has a nice slam to it, bass is superb, has great definition and is “evolving” due to the synth used. "Good Morning" by the same artist is also highly recommended, the bass on that track has even more impact and presence. A perfect example of the EST50s capabilities

Under My Sensi - Boozo Bajou

Another great match. Very airy presentation with great separation. As soon as the main bass hits, you are presented with a clean sound that extends well into both ends of the spectrum. Bass is present and reaches deep but not overly pronounced, the drums have great presence are highly detailed. Its a very coherent playback


Acoustic/World music

And I Love Her – Pat Metheny

Acoustic music on the EST50 is a real treat and this song is a perfect example of that. The guitar sounds amazing, you can hear every minute detail of the picking/strumming. The guitar has a nice body to it, the low end is slightly elevated but it sounds very natural overall. Perfect treble extension, sparkling with air. Its like being in a little room with the performer right in front of you. Perfect immersion

Cumbia Sobre el Mar – Quantic

Another great match for the EST50. There is a noticeable noise floor on this recording. This IEM will strongly show any noise floor a track/source has. It shows that they are highly sensitive but if you are like me and can’t ignore the noise it may annoy you on some recordings

Apart from that, the overall sound is very organic and rich. Great imaging, very 3d like. The bass is well defined, has great texture and sounds very lifelike. Drums/percussion are amazing. Nice separation, great airiness and a strong presence. Instruments are represented perfectly. They sound very true to life while the ESTs provide that extra bit of sparkle and air in the higher regions. Its a joy to listen to and really shows what these are capable of, sadly with the downside of a noticeable noise floor throughout the whole track. The vocals at 3:12 integrate well into space. They are slightly dialed back but still manage to have great presence and sound accurate. While the EST50 can do vocals rather well, they are not shoved into your face. They mostly integrate into the rest of the spectrum while retaining perfect clarity and presence. I am rather fond of this presentation, as it allows the vocals the shine while not being in the center of the attention. Which adds to the organic sound, it all just sounds very coherent

El Cuarto de Tula – Buena Vista Social Club (2021 Remaster)

Absolutely stunning playback. Instruments are nicely separated, vocals sound very true to life. Drums/percussion are clean and have great extension. The overall sound is very detailed and balanced. The upper end sparkles with great energy and extension, while the bass is very controlled and natural. There is a great sense of space/air around the instruments and the singers. Its a very accurate and lively representation of the source material


Rock

On The Road again - Canned Heat

Such a classic and always a great song to test sound stage and separation. There is a slightly noticeable noise floor. Gladly its totally gone when the bass comes in. The instruments have such a nice separation here. The voice of Canned Heat is portrayed beautifully and placed slightly to the right on the upper side of the sound stage. It sounds very natural, and has nice air around it. Instruments are absolutely stunning. The bass mows along with such authority, giving the song an incredible groove. Texture is great and very true to life. Guitars are detailed, with a great sense of space. Spot on imaging

Sultans of Swing – Dire Straits

A perfect example for how much source material matters to the overall sound response of the EST50. This song is presented in a rather neutral manner. Guitars are beautiful, Mark Knopflers voice has great texture and sounds very clean with a very slight reverb on it. The bass is controlled, keeps up fine with the pace and takes a slight step back. This results in the highs and mids shining even more. This also makes them great for listening to Jazz, if you can live with the slightly slower bass at times

School’s Out – Alice Cooper (2023 Remaster)

A great song to test how they handle micro details. At 1:10 and 2:16 there is a distant sound off to the right. Sounds a bit like an artificial cuckoo. Its noticeable and rather present when you focus on it. At 2:27 there are some kids making sounds. While the boosted laughter a few seconds later is very noticeable, its the ability of the EST50 to provide the little nuanced sounds at the beginning, perfectly separated from the rest of the spectrum

Apart from the impressive ability to present all the little details while still giving the song a nice and weighty presentation, it sounds great. The voice of Alice Cooper is great here. Incredible texture and presence, guitars are spot on, and the bass is nicely controlled but adds a nice warmth

War das etwa Haschisch - Georg Danzer

For anyone that says the EST50 doesen't do vocals, take a listen to this track. The overall playback is stunning with great imaging but the vocals almost pierce your brain with their presence. They are taking the center stage, while everything else is slightly dialed back. It feels like Georg Danzer tries to plant a message right into your mind. The overall sound is clean but organic, with a nice richness


Metal

No regrets - Accept

This track gives a perfect representation of the "brick-wall" type of sound these are able create. From start to finish you get a thick, slightly warm sound that still manages perfect separation. The focus here doesen`t lay on the sub-bass, which only plays a supporting role. This means the EST50 can hold up rather well with the fast rhythm of this track. Guitars have impact, vocals are clear and present, while the low end provides a nice base to the sound. These can be very engaging with Metal, this serves as a nice sample of their capabilities


Jazz

Dark Side Riddim – Ezra Collective

I love modern Jazz and Ezra Collective are one of my favorites. This song has a nice groove to it, the EST50 keeps up the pace effortlessly while providing a satisfying but controlled bass that has nice texture to it. Instruments sound nice, with a slightly artificial touch to the saxophone (but I think that comes down to the effects used). The piano is very natural, drums are true to life and have a nice air around them. The presentation verges on the side of neutral fun, which seems to be the norm with jazz music. "May the Funk be with you" is also highly recommended on these



Media consumption

This section deals with everything outside of music, with the focus on movies. It deserved its own section because I was rather stunned when watching my first movie on them:

“I watched "The Fifth Element" yesterday with my EST50 (Hiby R5 ii). What an experience! This really takes "cinema in your ears" to a different level...

The bass gives a subwoofer like theater experience while the imaging provides pin-point accuracy. Every launch, explosion, shot and even the "universe" (just watch the first 2-3 minutes and you`ll understand what I mean) are portayed in such an immersive way (at the beginning you really feel the sense of endless nothing), it pulls you into the experience like I haven`t experienced before with IEMs. You can "feel" the rumble when an engine is roaring, you "feel" the impact of every explosion and especially the highs (shattering glass for example) have such a nice edge to them. I will be using these a lot for movies in the future, its just another thing the EST50 does with ease and without any major flaws I can think of (except a bigger soundstage but with this imaging and immersive bass I really don`t mind and forgot quickly about it).

ISN really created something special here, this is the closest I have ever come to a theater-like experience at home and its very akin to a nice 7.1 system. And the best thing is, you get all of these amazing traits even on lower listening volumes “

Gaming, watching videos and making music is a joy on them. Excellent for media consumption



Comparisons

Phonak PFE 232

A 500€ flagship from ten years ago vs a 400€ flagship from today

The 232 were highly regarded back then and while I have to go from memory I listened to them for years as my daily driver. 3BAs that provide a fun but highly detailed tuning with great bass. Now the EST50 trumps them in almost every way, which is to be expected. But they still hold up amazingly well. The EST50 has way more bass but its a bit on the slower side, which means while the EST50 can struggle on a few select tracks, the 232 handles everything perfectly. Mids are better on the EST50 but no slouch on the 232 either. On the highs the EST50 win again, the ESTs are able to provide more excitement/air in the upper region without being sibilant. The sparkle the 232 is able to provide trumps the EST50 though, treble extension is great on them. They can at times be a bit spicy though


S12 Pro

The S12 Pro is excellent value for the money but the EST50 trumps them in almost every way for me. Bass is no comparison, while the S12 Pro left me wanting on a few tracks the EST50 always provides. The only pro for the S12 is the speed, bass is a bit tighter and doesen`t struggle with faster passages. The mids again go to the EST50, they simply sound more organic and true to life. Highs are another clear win for the EST50. The S12 Pro can have a slightly artificial timbre, which I don`t enjoy. The EST50 doesen`t have that problem at all. Treble extension is comparable but the EST50 provides the details more effortlessly and isn`t as prone to being sibilant

Are 300€ difference worth it? In my eyes for sure. If you got the S12 Pro and want more bass, a more organic and lifelike presentation, the EST50 should be high on your list. Its like a marriage of the 232 and the S12 Pro but brought up to todays standards



Conclusion

Having been out of the game for a while its amazing to see how far IEMs have come over the last 10-15 years. Its certainly possible there are better deals at this price for your money. But this is a special signature that will be hard to find anywhere else. ISN have a certain style they are going for and this is the pinnacle in execution of that style. Are they worth the money? For me its a definite yes. Never did I think it would be possible to give you this amount of bass while still offering a somewhat balanced sound. Guess that`s what a Tribrid can do for you and there is no going back for me now. I find it hard to fault much about them, they are a happy accident that etched itself into my mind. I am intoxicated by this signature and fear that anything more neutral will leave me wanting. Highly recommended!

After a good week, I still stand by these "early impressions"

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Hey there, I just revieved my Hip Dac today and have been listening all day.

The Hip Dac sounded great from the beginning (after about 20 minutes I changed to the newest firmware) but gets better and better (about 7 hours in). This pairing is something special. I have had my 232s for more than 5 years now and regret that I never gave them a source they deserved.
I drove them with my Iriver H300 which does not sound bad but is nothing compared to this.
I also listened over my laptop (Xiaomi Mi Notebook Pro) which sounds suprisingly well but lacks the depth, clarity and low end in comparison. I also used my phone from time to time (Blackberry Passport) and while it does sound decent it also lacks a lot in the low end.

Now let me tell you this pairing is pretty much perfect.
I get zero noise although I have to be very careful with the volume control or it will blast my ears out (I just discovered that when I actually listen for it there is some noise floor on high volume with quiet passages, so its not zero. With most tracks its not really noticeable though so maybe I will just ignore it).
The 232s have a slightly v-shaped sound signature and this player has a bit of a boost in the mid range and low end which makes the 232s sound pretty amazing. This little thing gives them the creamy mids the 232 does not deliver normally.
The low end is phenomenal. Now these already have nice and controlled bass with insane low end extension but paired with this its truly breath taking at times.

On many tracks I find the x-bass too much and it makes the sound too muddy.
On the right tracks though this is great though.
This shows what the 232s are truly capable of in terms of low end. With psytrance especially the bass is out of this world good. Which it was even before but with x-bass it completely blows me out of my mind while still keeping most details and nice highs. Best bass boost I ever heard, just wish there were some levels you could switch through as on most songs I actually thinks its a bit too much.

The 232s end up sounding relatively neutral with very nice low end even without x-bass and a slightly warm sound signature which I enjoy quite a lot.
Now its of course not the best dac in the world and neither the best amp but for this price its fantastic.
While I don`t own any high end dacs or amps I can only compare it to the best sound card I have, the Asus Xonar D2X.

This is a fantastic card with lots of details and an amazing sound stage but sadly I lost a connector for it and have not been able to use it for some time now, so this is all from memory. The D2X definitely had a way better sound stage.
Not that the Hip Dac has a bad one, but its not that wide and lacks some depth in comparison.
It also wins in the highs and mids, but only slightly in the mids. The low end is another story though.

The D2X is a pretty flat tuned dac which results in very nice controlled low end but sometimes I wished there was more and sadly there is no option to increase it via the driver. The low end on the Hip Dac is very good.
Without x-bass its pretty much the perfect amount for me since it is slightly boosted but it does not sound muddy at all and overall it sounds simply amazing. X-bass is for when I want that extra juice but I find it very genre and track dependent.
Since I listen to a lot of electronic music I think it fits psytrance the best out of all I tried so far, with hip hop it got easily too muddy and techno was nice but also a bit much with some songs.


All in all the Hip Dac comes pretty close to the D2X in highs and mids and the lows win it for me for sure.
It does not sound as refined and detailed but more musical and since the 232s don`t really lack details its a match made in heaven for me. I am sure there is a lot of better gear that will blow my mind even more but for now, I could not be happier.
My 232s have never sounded so engaging and fun. My only gripe is the battery life and the very limited volume control range (not the players fault though) so far but I knew what I was gonna get myself into...