Headphoneus Supremus
Pros: Sonion EST treble refinement X2 per IEM
Exotic one-of-a-kind bass personality
Smooth, highly detailed midrange with a soundstage within a soundstage
A mid-fi IEM that thinks it’s in the big leagues, and performs accordingly
Great technicalities
Endearing pace and rhythm showing ISN’s soul and individuality
Beautiful and highly detailed faceplates
No pinna gain heat ever
Includes a cable manufacturer’s level of cable due to ISN making cables
Lightweight/perfect fit
Scales up, up and away into TOTL flagship levels of reproduction
Cons: Bass presentation levels could be subjective, no matter how sculpted and refined
Limited included extras in box-opening experience
Ahh, the music’s pace which is starting and stopping; all those bumps that get you going. Those small rhythm-twists that are a moving! It’s maybe not the sound, but the airspace between the notes that make the beat move forward? It was the gyrations of Elvis’s hips, you know the ones they couldn’t broadcast, that’s where Rock-and-Roll lives. The attitude you have by yourself when you’re jumping around in your bedroom before school. It’s truly the stuff you can’t see or hear that holds this magic. The way the build-ups and breakdowns take place, it’s simply movement………… like water over a waterfall. You can’t stop it……’s maybe life itself? You’re about to read about a humble IEM that contains the above Rock-and-Roll essence. The ISN EST50…….a simple $459.00 IEM. And no, the EST50 is not finicky or prudish, no, it’s a joy for everyone who wants to partake. As that’s how it should be………..the spirit of should be free, or at a small cover-charge. Don’t you think? It’s maybe part of the bass and drum communication; some style of interaction? Tight jeans and go-go dancing miniskirts. It’s a Chinese IEM, but it plays rhythm like you never-heard, at least I have never heard. A souped-up low-end which moves this whole shebang forward. Yet it’s tight, and epic big……….big as all get out. A true ISN flagship! The flagship is one IEM model that companies are most proud of, the one unit a company has singled out as their ambassador. So when Penon Audio asked if I wanted to review the EST50, I got super excited. Why?


The flagship… a statement, it means they are not messing around. This is the best the company can do! Let the product do all the talking……………this single product is who ISN is.


The best way to understand the sound of the ISN EST50 is to go back to the ISN H40. In fact the H40 is the start of the ISN house sound. In December 2019, when the H40 was introduced, ISN was nothing more than a cable builder with bright dreams. Hopes and dreams of one day of becoming a world-class IEM maker. The 2BA/1DD $195 H40 put ISN on the map, so why wouldn’t they expound on the signature by bringing in more hardware? Finding meaning in what the H40 did/does is key. The very reason for the H40’s popularity was big bass, expansive soundstage and uncanny treble and mids. It turns out the when the H40 was introduced they made a few…..then did a quick retune.........which in turn left ISN with old (sounding) stock. So the previous version of the ISN H40 and the retuned version where both included to early buyers at no extra charge. And the rest is history so to speak. If you read reviews of the H40, they really reflect the fundamental ability of a Hybrid to bring more. People were/are calling the H40 their personal deserted island IEM. And the H40 continues currently as a statement product of the ability of ISN as an IEM company. But due to the laws of nature, no matter how good a $195 2BA/1DD can be, it can only do so much. Probably nothing in my IEM collection (of recent-times) emphasizes how much sound-advancement has taken place since 2018. With the ISN H40 sounding better than the $600 IEMs regularly found for sale in 2018. So you can only imagine the springboard effect going on with the EST50. It also doesn’t hurt matters that the H40 and EST50 match my personal desired sound-signature.

The EST50 states = progress is progress for ISN.

Also newly added to the ISN legacy is the different $295.00 4BA/1DD H50. Introduced in November 2021 the H50 is in-fact a farther departure from the regular house-sound of the H40/EST50, I am told. I have yet to hear the H50, but it’s coming-up. So even though the H40 is from December of 2019 and the EST50 from July of 2021, they share a common theme. And why wouldn’t the EST50 advance the tonal ability of the H40? The H40 was truly the genesis of all things ISN. The H40 is their mascot, it’s who they are to begin with. So the path was already set-up to go a grandeur place, at a price. Whether or not to pay the asking $459.00 over the H40’s $195.00 cost is a big question. The $264.00 up-scale surcharge over the $195.00 H40 is up to you. This isn’t a question of the H40 doing something different as the H40 and EST50 are tuned the same. Such is the value placed on diminishing returns per dollar spent. But you have to wonder what this added hardware brings? Technicalities maybe?

It’s like the H40 is the sound of a large bus, and the EST50 is the double-decker bus following right behind it. If you think ISN simply added some fancy Sonion ESTs in and called it a day, you’d be gravely mistaken. Such is the DD of the EST50 so different, so vastly superior at doing the same general tone of the H40………they maybe should have called it the DD50? Yes, I’m showing my affinity for bass here, but still the EST involvement is there but small, none the less. Due to the inherent lack of ability for EST drivers to do lower treble well, they become fully designated as ultra-high detail providers.

I would like to thank Penon for the review sample which was provided for the purpose of review, you can buy them here.


End of Review:
Above is all you truly need to know to make an educated purchase. The ISN company made an L-shape bass heavy IEM called the H40, it was successful (due to being so balanced and evenhanded) so they upped the sound and created an expansion in pace, instrument-tone and soundstage detail. Such better tonal and epic technicalities were a conquest to see if the H40 could be refined and the sound brought further into reality. This is what crazy perfectionist IEM sound designers do for a living, they can’t help themselves. Lol

If you do continue to read on you will be indoctrinated with more just like the above, yet in greater detail.

Who is ISN?

In the beginning ISN made only cables; and even now they keep introducing new cable models. With 17 currently made different cables, it’s no surprise they understand what makes cables different from one another. If you by chance are reading this review as a steadfast cable non-believer, that’s ok. To have a company offer such a wide range of essentially the exact same audio-cable could be judged as ridiculous, or worse…………..ISN is the epicenter of audio-snake-oil. But wait, there’s more……….

To add fuel-to-the-fire, the EST50 seems to respond to cables more than most IEMs. So imagine that one! A cable company offering an IEM that actually responds (more) to cables changes. It’s a conspiracy no doubt, if you are a cable non-believer it is. Unfortunately wisdom only travels into an open mind and just like you (the non-believer) I had my prior understandings altered. If I could, I would like to offer you a single quote.

“Cables are a hot topic especially for enthusiasts. The IEM cable market nowadays has seen so many varieties and styles to choose, when it comes to cables. The big debate is do they actually help shape sonic qualities? On one side of the fence the objectivist enthusiasts do not believe in cables making any difference at all. I understand that notion but on the other hand there are people like myself that write cable reviews and talk about their finer qualities and how they affect sound for your earphones. I suppose my review here will help the folks that do like a good sound shaping cable to help with their IEM sonic profile more so than the science guys. My honest take on that is. Believe your own ears”

End quote:

So simply believe your ears. Truly it should not get in the way of hobby enjoyment, simply do what works for you. Unfortunately cables will end up being a big part of this review due to their sound shaping abilities. Cable non-believers can either deal-with-it, or move on to another review, as I’m not trying to sway anyone one way or the other.

The ISN Company:
ISN current cable offerings:
Silver-Plated IEM Cables: S4, S8, AG8, S16 and one Type-C Silver Plated USB Cable
Copper IEM Cables: C4, CU4, C16
Mixed Cables IEM Cables: Solar, G4, GS4, SC4, H8, H16
Gold-Plated IEM Cables: GC4, GD4

Pure-Silver IEM Cables: AG8

ISN Ear-buds:
Rambo 2

H50 10mm Composite DD (bass) 2 BA (mids) 2 BA (highs) $295.00
H40 9.2 DD (bass) 1 custom BA (mids) 1 composite 2BA (highs) $195.00
D02 10mm DD $79.00
D10 9mm DD $169.00

EST50 1 Knowles BA (highs), 1 Sonion BA (mids), 10mm DD (bass), 2 Sonion ESTs (ultra-highs) $459.00

Strangely, even-though making all this complicated stuff, ISN describe themselves only with one sentence.

“We are a wire production and R&D factory.”

ISN is special:
Such minimal descriptions can actually go along way to explain the small niche we are visiting today. The ISN sound is one-of a-kind, thus offering for people a style of paradise island. If you are into this sound, and want to pay for this style of reproduction, all the rest of the aspects are taken care of as well. The build quality, fit and usability are perfect examples of the art, showing that ISN is fully into it. That in-fact they too live on this small island, offering a very special style of magic that can only be found at this single local. While $459.00 is a sizable chunk-of-change, it is by no means representative of how much you can spend on a single set of IEMs. Here with the ISN EST50 I find complete satisfaction in knowing this represents one example (if not the best singular example) of fidelity for the money. A mid-fi offering that doesn’t know it’s mid-fi.


The packaging and unpacking experience leaves much to be desired. Though the metallic-blue-box IS original, and you are given most you are going to need. It may be looked at as the bare necessities only? This is a style of tough-guy territory…….it’s like “Here you go.” “Take it and like it.” I was sent the H40 and the EST50 simultaneously, and the H40 comes with 12 sets of ear-tips in comparison to the 5 sets the EST50 includes. Then I started to understand the contrast in added extras. The H40 is more of an entry-level purchase and that style of consumer would be more prone to experiment with a range of tips. On the other hand, the EST50 customer probably already has their favorite ear-tips and wouldn’t even use the included ones.

Then you start to look closely at the IEMs themselves, then something hits you………Oh?……….they are absolutely beautiful. You just went from 0-60mph on the “I’m impressed speedometer”. You think to yourself………..that’s right this is the flagship! I have the ISN EST50 in green, but they come in blue or stabilized wood faceplates. The rest of the shell is dark translucent-blue with nice flush two-pin sockets. The look of my green color is never captured by photos. There are mixtures of green and purple metallic dust which gives the EST50 a gem-like quality. Such a sight that almost looks liquid, almost moving? Light traverses across the faceplate, yet never goes the full extent of illuminating it 100% all-at-once? It is this mysterious ability that lets you know there is always more around the corner with the EST50. You never see it straight-on, same as you never hear it 100%……’s always leaving more hidden………yet waiting to be discovered. The build is fantastic, and the seemingly flawless execution of form goes miles to have you forget the minimal extras included in the package. Any thoughts of disappointment from the box-opening ceremony fades as a distant memory if even a memory at all. They put the effort in the construction, the EST50 looks like a flagship. Such effort doesn’t go unnoticed as the craftsmanship tells a story. The nozzle is on the longer side with a formed lip which seems to work way better than you would guess (by looking at it) to hold tips on. Looking down the nozzle we are greeted with three bores.

2 Sonion Electrostatic driver for ultra-high frequency
1BA Knowles for high frequency
1BA Sonion for middle frequency

10mm dynamic for bass

Such an arraignment-arsenal of drivers leaves nothing more to be desired………at least I want of nothing more sound-wise. Somehow every small hole in the audio spectrum was filled in by the complete frequency response combination? But more than just filled in, we are gifted with the total experience…….the musical experience in its entirety, complete with emotion and grandeur! The TOTL Flagship experience which separates the half-attempts from the full-actualizations, and just goes to show you where your money went.

  • Model: EST50
  • 2 Sonion Electrostatic driver for ultra-high frequency
  • 1BA Knowles for high frequency
  • 1BA Sonion for middle frequency
  • 10mm dynamic for bass
  • Rated input power: 2mW
  • Max input power: 3mW
  • Impedance: 18ohm±10%(@1kHz)
  • Sensitivity: 100±3dB(@1kHz)
  • Frequency response: 15Hz-70kHz
  • Color: blue , green , orange
  • Connector: 2Pin 0.78mm
  • Plug: 3.5mm audio , 2.5mm balanced , 4.4mm balanced
  • Cable length: 1.2M
The Sound:
Headphones are like cheese in that there are fans of different flavors but some flavors don’t attract many. There is in fact no right and wrong to headphone playback, except different variations of even, complete and correct renditions of the file. Such variations of FR do display a level of correct playback. With extreme variations showing only a small niche of true love. That’s OK, as always it’s a bell curve.


The EST50 marker is in relation to texture and bass timbre making it possibly accessible to more people? But in truth the ISN EST50 marker would be at the left occupying directly over the "Bassheads" designation.

Response to source:
Probably one of the most fascinating things was testing the ISN EST50 from an expensive desktop, then going to an Apple iPad. In this case I truly thought there would be more difference between sources. Of course the desktop offered wider soundstage and more realistic imaging, but surprisingly the overall authority of playback was found from 320kbps from an iPad. So a total plus for the EST50. Using two different sounding DAPs it still showed the tonal changes and well as the different soundstage placements. The Sony WM1A is more midrange forward and because of this the bass is tighter as well as the mid-tone expands the soundstage out more side-to-side than the WM1Z. The WM1Z has more front-to-back soundstage positioning, and the EST50 showed that. The WM1Z offers a more complex imaging, and spread-out treble which the EST50 showed. Where the fun really started was using the included ISN S8 cable and going to the Sony TA-ZH1ES desktop. The TA-ZH1ES was supplied music streaming in digital form from the Sony Cradle and Sony WM1A DAP. The interconnect from the Cradle to the TA-ZH1ES was the AudioQuest Carbon USB. I even utilized the DSD Remastering Engine, the DSEE HX and the DC Phase Linearizer. Such fancy processes are just names for a kind of up-sampling effect. They do more than up-sampling, but let’s leave it at that. Such a set-up truly showed what was possible with the EST50. Imaging contrast improved from the DAP use, as well better improved pace and transient response. Lets me stop here…….everything was better. In fact, getting the desktop power to the EST50 helped show what could be termed reference playback for the IEM. Now to be fair even iPod 320kbps was only a small fraction less (night and day) :) but still it shows the EST50 has the ability to just keep scaling up and up. Firmware 1.03 in the TA-ZH1ES has less brightness than the WM1Z does naturally, but somehow it wasn’t an issue. Meaning you think a warmer IEM may need some extra sparkle up-top in contrast to the fully darker TA-ZH1ES sound, but nothing could be farther from the truth. With the TA-ZH1ES the EST50 was in its element. I also came to the realization that soundstage in this situation was fully brought about by the song file.

Interestingly the soundstage is very dependent on how the recording was made (way more than I have ever witnessed). So modern day hi-res recordings boost the space you are in, compared to low quality old files. Now it needs to be said the EST50 is forgiving of (further away) inept recordings by using its warmth to do away with thin sound. Even older recordings are brought to life with the soundstage present with the EST50. This last statement may appear to contradict what I just stated, but the two concepts are different. Meaning older recording are still brought to life due to the nice natural soundstage; that is connected to reality. Also older recordings get sonic forgiveness that comes with a warmer/colored IEM sound signature. So in summery the EST50 just displays what soundstage you give it. Get it incredibly big soundstage files (with optimal source) and prepare to be amazed. Testing side-by-side IEM comparisons gave me a broader understanding of what the EST50 soundstage is. The ISN H40 has a forward placement of sound being big and authoritative. The EST50 takes that forwardness of the H40 and positions it way back, to make room for the texture and imaging elements to come forward. So the H40/EST50 are using the same size (soundstage) room, only the furniture was pushed back against the wall with the EST50. Then the lights were turned-up to give a better view of the detail of the furniture. Thus the furniture in the end looked more real. Any smoke that was in the room before with the H40 was cleared-out for the EST50.


The soundstage sonic-profile:
The S8 cable was used, not only because it’s the included cable, but because I truly like it.

S8 Cable:

  • High purity makes the cable extremely soft, providing the comfort of wearing,
  • Gold-plated plug is more beautiful and durable, using insulation treatment technology.
  • Natural and transparent sound, delicate and smooth; lift medium and high frequency, strengthen high frequency extension
  • Model: S8
  • Material: Single Crystal Copper Sliver-plated
  • Number of cores: 8 shares, single share is 19 cores, a total of 8 × 19.
  • Connector: 2pin 0.78mm
  • Plug: 3.5mm audio/4.4mm/2.5mm balanced gold-plated plug
  • Cable length: 1.2M
Yep, I just put the S8 cable specs in the soundstage sonic-profile area…….so sue me? I will say that with every cable change there was a tonal and sound positioning difference. The main theme of this section is that even though new cables brought with them a change of tonality and positioning placement, it wasn’t always natural. So there is something to be said of the overall S8 quality to provide correct positioning and tone! All and all the S8 included cable is slightly brighter than some OCC copper cables. I would guess the S8 was chosen as it’s not expensive, but is a great all-rounder and gets the job done. The S8 is the Toyota Camry of cables. The signature here is a playful display of upper treble out in the outskirts of the stage. The bass finds itself often centered being full and round. Still the excitement comes from complete separation with big and authoritative adds. World-class imaging and decays. Drums do that panning like you’re witnessing a live drummer. At times a bass mix is in two places simultaneously, mixed into the main center, then often for effect, sent out into the soundstage. Obviously the producer intended such shenanigans, but rare to be able to hear it. All I can say is the soundstage will upscale with better equipment and once you are there, it’s totally big and beyond description. I mean the soundstage is everything right? It’s the canvas for all the sonic elements to take place. Inside of that area the elements exist to show their realness and timbre/texture. There is nothing wrong with S8 in addition to your very best equipment………… reason to be a cable snob.


I did probably 20 cable change-outs while using 4 different cables with the EST50. This is by far the most I have ever done in a review to date.

1) The included S8 cable (Single Crystal Copper Sliver-plated) 4.4mm
2) Han Sound Audio Zen 4 wire OCC litz copper cable terminated Furutech 4.4mm
3) DUNU 8 Core, High-Purity Monocrystalline Silver-Plated Copper Litz Wire DUW-03 4.4mm/3.5mm

4) The SANDS silver-plated cable 4.4mm

All this talk about cables is simply like adding equalization to your rig, except cables also influence positioning inside the soundstage, and different than EQ, can change imaging size of particular instruments. With changing amps, tips and cables we are able to slightly modify the tone and soundstage. While this can be individual preference, I can’t help but believe a natural imaging placement and correct tonality is what is strived for? While at times a cable would seem to add correction, except then hours later the imaging layout wasn’t totally right. I will say my most used cables with the EST50 was both the HanSound Zen 4 wire, and the included S8. Both cables seemed to offer great clarity as well as correct imaging. The S8 being silver-plated offered slightly more brightness than the warmer OCC HanSound. The way the EST50 is, using either cable was a joy, and you were never looking for correction or change. Typically (if I understand it correct) a person will gravitate towards a certain cable style and get deeper into believing in the model or model group. What is taking place is familiarity and understanding. They may chose a metal-makeup for a certain IEM response character, but often the same cable will be used on many IEMs. Some of this is psychological, and some is just that cables each can have a different sound. There is no right or wrong to it all. I suggest to find an aftermarket cable to at least experiment with. The S8 is one (new-to-me) special cable, but over the years I have used the HanSound Zen with most everything to great success.


I used about 8 different pairs of tips. Due to nozzle length it seemed like I would have done better with a size smaller? Meaning for some people the further you place the nozzle into your ears the smaller size tip you need. Still the over-all character of the EST50 was always in focus. Never did I find I needed a tip for sound correction. Meaning the EST50 simply offers a wide range of sound experiences due to tip change-out, and none of them are wrong. Wide bore was great but ended in being the most finicky in fit. You will not ever be needing to find a tip which adds nozzle length, that’s for sure! Lol


Burn-in is real in this case. Go ahead and read the other reviews. Whatever it is the EST50 and the H40 both offered woolly and one-note bass upon listening to them pre-burn-in. At 50 hours they were great, and at 100 hours they seemed to reach their place. Their place is sounding normal and optimized for music reproduction. With burn-in the EST drivers seemed to become more relaxed and agile? At times burn-in creates a small change, then other times (like this one) it’s a big deal. Don’t shortchange yourself, just do it!

est 3.jpeg 34.jpeg 2.jpeg

Bass gets a lot of flack, does it not? For some it’s the (bass) linebacker keeping them from reaching sonic nirvana. For many, it’s the fly in the ointment. For some it’s paradise. Go figure? All I will say is the bass is beautiful here. As exotic and fascinating of a realm as you will ever find in IEM playback. It’s the two-times double-punch, 1 + 2 that has both authority and texture. That’s it…..simple. It’s real bass, like hearing the instrument played live. But more than that, it’s creative in that there will be new accents found in songs you’ve heard your whole life! These filagrees have maybe always been there, but seem to come-out and surprise when least expected. Such musical forms also hold the backbone of the music a good portion of the time. Like explained in the opening; this also has to do with what is not heard. The silence between the notes, which brings about a level of pace……that’s what I’m trying to get to. Still the EST50 is not perfect. It finds its trouble in super fast passages. At times the bass notes become coalesced. It may sound contradictory………..but both pace and anti-pace co-exist in EST50 replay? You have to be prepared to live in this neighborhood we are visiting. It’s not like an on-off phenomena, but more like a low volume connection between every bass note. Where the bass energy upfront is clean, at times the bass can’t get out of its own way. Still……………………just like being in love, you make compromises. Cable changes and DAP changes did reduce this effect (almost completely) but then a little of the soul was lost at the same time. In the end this is L land, though a unique and rare L land none-the-less. Such bass is new in my IEM listening experiences, in-fact any artifacts (I guess) may simply come with doing sub-bass so low. It’s both the depth of the bass and the added amount (from normal bass) that is bringing about this phenomena. What is created becomes a different way to hear specific musical passages, with new and different nuances and new-found textures coming to light. You will find extra small bass-details, which are both defined and exposed for what they are, which always have been there, but seemingly left un-excavated before? Such a journey into sound is not without its consequences. Though there is never fatigue or boredom from such endeavors. Often though, you may encounter slight collateral damage, as such bass cannon-fodder that simply can’t be avoided with subterranean levels.

est 50 1.jpg

Nice separated cymbals and shakers, still not exactly bright of even fluorescent. Reading 2X EST may be misleading? Yet it isn’t boring at all, like you think it would be from reading the above. I can still hear all of my (non-IEM) equipment’s character, but it’s slightly slanted. The meandering bass has a top-off here. They are made for one-another. It’s all there, all the frequencies, yet there is still not that much of a contrast……..even the brightness is taken down a notch. Somehow this provides absolutely zero metallic BA off-timbre, as it’s maybe hidden from us, if it is there? They (ISN) won’t allow the treble to spoil the darkness here. The magic is that just enough information is coming out of the woodwork............what is there is fully detailed and dimensionalized, still it wouldn’t be considered sparkly. You’re not buying these for the treble anyway. This treble section may scare a few off, but there is nothing to worry about. It’s like going into that amusement park ride and wondering if it’s dangerous or not, but once your aboard, it’s fantastic and a blast!

The midrange does a lot of the work here, the mids have to hold-down the ship. That’s just how it is. The bass and treble can screw-off but the mids are truly the hardest working segment here. The mids are where most of the musical information is. With some playback combinations vocals were slightly set back, and with others they were fine. Most of my gear is on the warmer side, so there is always that danger of the mids being lost, plus vocals set back due to the source. Here the midrange walks a fine line as to not get in anyones way. My most favorite aspect of the midrange is the violin or organ accompaniment, that sits way outside the soundstage, kind of like it has its own separate soundstage inside of the regular soundstage. I hear this in many, many songs so I know it’s a thing the EST50 does on a regular basis. These strings have timbre and instrument tone, as well as relief from what’s behind, or really next to them. They also have their own individual reverb, that makes them precious. Due to the EST50 not being a vocal IEM, there needs to be others aspects which fill the void, and that’s what is taking place. I actually come from a lifetime trend of enjoying instrumental music, I mean, why let vocals come along and ruin the show? The instruments have work to do, leave them alone. I have come from a long term enjoyment of vocal-less music and as of recent only just began to appreciate vocals for what they are. I’m not saying the EST50 doest do vocals, it’s just not a focus.


Sound generalizations with the WM1A DAP and WM1Z DAP:
The ISN EST50 comes off the polar opposite of the TMSR Sands IEM I just reviewed. Even though each IEM is concentrating on a different area of the frequency bandwidth, they both show a complete, even and correct frequency response. Where the Sands is primarily high treble and a faster bass, here we are met with a fully explored bass sector. Though contrary to what you might guess; it’s done in such a way as to leave room for the rest of the response to flourish.The forward midrange of the WM1A seem to bring stuff just slightly closer? The intrinsic ability of the WM1Z is bass realness and brighter treble-add dynamics. I was curious as to the low-end effect with the WM1Z and EST50 combo? I was wondering if the added bass emphasis of the EST50 would be too much bass? And while such low end does reduce the pace factor just slightly, there is a realistic bass quality that the Walkman WM1Z does anyways that joined with the EST50 is the cat’s meow! It’s this bass authority that has a way of being the escape vehicle, taking you off into bass land. After spending the better part of a week with the 1Z/1A combination, I ended not having a favorite with the EST50. Both were my favorite, each allowing another dimension to be explored. As it wasn’t about putting out any fires so to speak, but seemingly finding home in how each parleyed the music.

Usually testing takes place with the use of 50 or more individual music examples. With-in these samples I am attempting to ascertain the presence of all the qualities described in this review. But to clarify and communicate concepts, I always choose a relatively small group of recordings to act as definitive examples. This occurs for two reasons, one they are good recordings, allowing the full-spectrum of musical playback process to take place. And two, I know them the best after using such examples for years and years.


4.4.1 kHz - 24 bit

The very opening parlays contrast and vibrancy. A formal bigness and a spread-outwardness that reminds you the EST50 this IS their flagship. We are entering TOTL town and the EST50 is not going to let us forget it! The size-of-it-all walks us through this number, possibly distracting us with use of simplicity. Really Amnesia is not a super-heavy bass song. Some how all is in place and natural. Besides the single string metronome, at first it’s really the low piano keys that get our attention. I always forget just how big the piano can sound. The bass of this song is fused with the piano keys and they introduce themselves simultaneously along with the drums. The strings have found their own little soundstage inside the soundstage! At 1 minute 12 seconds the vocals start. And even though these are not vocal IEMs they are just fine. Brendan Perry's vocals can be reproduced slightly different by every IEM. Where Head-Fi is at times all about absolutes, here it's simply another color on another day!

The EST50s are the IEM equivalent to floor-stander speakers, there is no denying that, the only difference (from speakers) is they are closer to your ears. Woody, thick, and full-frequency. Brendan Perry’s voice is captured well, the way it’s done is not it anyway wrong. Honestly I have heard renditions move the vocal trajectory slightly more forward? But the kicker is it’s fully separated and in relief against this audio-backdrop. This is maybe the Hybrid magic doing its tricks, because everything has its place in the soundstage. The highest instruments even make their way-out further. Meaning I’ve heard the leading edge personality of EST drivers before, yet here it’s less noticeable.

Probably the pace that gets created due to the slight variations that are now heard inside the bass notes. Such clarity is an easy trade for a slight loss of pace. The magic though is inside of that bass rhythm.................a note gets kicked out and exquisitely you never heard before. It’s this rolling and tumbling way the bass and drums interact that’s so much fun. This 10mm liquid silicone dynamic “woofer” is not only doing what it’s told, it is almost playing bass parts I’ve never heard in this song. The bass emphasis is even more filagreed and accentuated even though strong? The bass is finessed and highly refined yet also slightly sloppy, if that even makes sense? The only reason there is slight sloppiness is the bass can’t get out of it’s own way fast and enough sometimes? Yet with this performance there is that uncanny ability to truly capture the essence of the rhythm? That’s why you could care less about any missing pace, leave that for the other IEMs.


Hans Zimmer
The Dark Knight Rises OST
192 kHz - 24 bit

Gotham’s Reckoning:
This song offers two examples for use today. Meaning such sound reproduction goes the needed length to make my points. Such individual spectacles lend themselves due to style of recording (sound-quality) and character of tone. 1st up is the bass that starts at the 19 second mark. I have used this song to demonstrate music for years and years. Yet somehow more bass character has been discovered. Part of that could be explained-off simply as more sub-bass, but I know for a fact there is more to the equation. As I go from the Sony WM1Z to the TA desktop what is taking place is obvious, there is a sensitivity taking place here. A subtle showing of both finite volume levels and texture. I could also shoe-horn in timbre too. Basically it’s all here, more than what I thought was inside the song-file, and that’s the reason I have never had a bass experience quite like this one today. At 31 seconds the lowest bass note in the song possibly takes place? Such an event is seemingly an entire individual character with the bass positioning and form. It is smooth as pudding yet is also of visible contrast. Such an event is simply getting closer to the sound and becoming immersed in the tone samples. It is like I’m now smaller in size as the music is bigger? I have become a sidewalk observer to something more happening, it’s simply more life-like and more real. Real because now I’m witnessing the event up-close and 3D. The second interaction takes place with the wooden claps. At 47 seconds appears a clap. Truly I don’t know what makes this sound? It could be a time-altered sample file of something else, it could be wood strips in the recording studio slapped? The importance here is at what tone they are replayed at. I have used this single sound on maybe the last 15 IEM reviews. Reason being is it’s never played back exactly the same every time. The sound has timbre, tone, decay and resolution, but the most important aspect it contains here today is spacial positioning in the soundstage due to frequency. So just like vocals which can set-back or forward, we are met with a position of replay. All this is also determined by what sounds/exist to be heard around it, but we will leave it simple like. It’s probably a hair too dark. It’s not a deal breaker, but it is what it is. The fact that if I had never heard this song 100 times, it would go unnoticed. Still it is an important clue in understanding what we are working with. Just to show how fickle this business can be, a switch to the “Sands” silver-plated cable brought the “claps” directly into the foreground. Though using the “Sands” silver-plated cable compromised the bass tone. So it ends really all choices with the EST50. The EST50 equals the ultimate chameleon.


Daft Punk TRON: Legacy OST
44.1 kHz - 24 bit
The fun here is I finally was able to get the Legacy OST in 24 bit. Also this new master offers a more robust yet smoother replay. Much of the heated red-line recording artifacts have been diminished, even though I thought they were permanent? It just goes to show how they are able to give us different corrected albums. Here the strings right-off combined with the syncopated synth are truly natural. Some how the low-end finds its own area in the soundstage? At 14 seconds you can only imagine the impact of the composite EST50 blast. Strings, drums and most likely samples which go along way to add the main-theme emphasis to the number. These are simply signposts leading up to the big EST50 blaster at 51 seconds. Daft Punk totally understand how humans are impressed. They understand buildups and cycles impregnated into the writing process. Still, maybe of any song, this number really goes to show it is part of a bigger work tapestry. But in the middle of the listening session we don’t want more, just leave us with this perfect moment in time. The drums are huge! Of course it’s the string section which holds the path we walk down. At 1 minute 47 seconds the reoccurring theme music starts-up once more in a way to show we are home now and at the end.

The ISN H40 $195.00 universal IEM vs the ISN EST50 $459.00 universal IEM:
ISN H40 review coming at the end of the month.


 12 cover.jpeg

3BA+1DD Hybrid:
First off I would like to say the H40 deceptively does a lot with a little. Meaning to better it they had to take a step back from the H40s more forward and in-your-face presentation. Such a character can often be tricky in these side-by-sides as forwardness isn’t always better, but just like fast-food can offer that instant gratification only to have you maybe wanting more as time passes. The H40 is a hair more efficient. First noticeable is how the EST50 effortlessly fills in the sketch work done prior with the H40. Such examples of playback start with simple elements in the soundstage sitting farther away with the EST50. As with prior expectation bias, I thought maybe the EST50 bass would be way louder or stronger or something different? When in-fact what takes place is more detail and better controlled/realistic bass-timbre. Such textures exist to be heard somewhat farther away, yet existing because of that distance. Where the H40 is more all-out 100% (in-your-face) with everything, here the EST50 takes a casual step back and creates a more real replay. Such replay takes place with strings with the H40. With the EST50 those same strings fall into a different area of the soundstage while occupying better 3D texture and reverberated nuance. Vocals are also slightly set back yet more clear with the EST50. The important part is the vocal detail in places where the EST just sounds more human. Such detail is what we pay for and are awarded. The H40 has a slight area of midrange congestion where things are just slightly clumped-together, where the EST50 takes that area apart and separates the elements for closer inspection. Now take note, often these differences would not be noted between the two IEMs, as it’s only under close inspection do these variations arise. Musically they are very close, but someone got out the Windex and cleaned the audio glass with the EST50. Meaning they occupy the same tonal arena for the most part. Yet the pace of the EST50 goes miles (off better) to show us there is more over the horizon. Such dimension exists and tells of more truth and clearer stories. The facts are there is nothing the H40 can do that the EST50 can’t. Such is the main goal in development, to bring about a more mature and refined sound. The fact that the EST50 clears off a little of the fog the H40 has, allowing us to see father into the soundstage and partake of slightly deeper timbre. The H40 has the uncanny ability to project a big sound (every instrument) but at the same time those sounds are hollow (hollow in shape, not sound) and without character in direct comparison. I’m actually doing a stand alone H40 review next, and no worries as the sound quality and value are there with the H40. It’s just you get what you pay (additional) for at times in audio. The real kicker is the fact that both IEMs fall under my description of a “golden-retriever”. Such nomenclature goes to name how an IEM acts in relation to source and file quality. Both IEMs don’t need catering to. Both IEMs gain pleasant playback from any source you have. Often at times we are trying to thread a needle by finding the tonal response that is acceptable, either by cables, tips or source choice. Here there are no such fires in existence to put out. So what we are left with is great tonal response and entertaining soundstage and all the rest of both technicalities and FR that make a winner. You just have to decide if this level of bass interaction will be distracting or not. It is distracting for me, but in the best of ways. So to sum up the H40/EST50 comparison, the EST50 comes through by doing the technicalities better therefor becoming a more detailed and real style of playback. With-in that realm of technicalities we witness the formation of actual real-life instruments and vocals. I see H40 usage with EDM outside of the house, due to it’s amazing low-end and natural noise occlusion, and the EST50 being more inside, where a more introspective and contemplative life-role takes place. The thing is, how often do you get to chose the same tonal signature in two separate IEMs? Here you could actually buy both and have the same sound signature, yet one less detailed for the outdoors, and one family heirloom to keep safe at home.

TRN Bax $312.88 universal IEM vs the ISN EST50 $459.00 universal IEM:

Flagship 1BA+1DD+2EST Hybrid:
One of my current favorites is the TRN Bax. The reason I’m bringing it up is I listen to it all the time. One reason maybe is it’s still new, being introduced in early April of 2022. So technically we could still be on the honeymoon phase. Whatever it is the Bax has the super-car look.


Would you agree, it looks like a car? I mean all that chrome and heat exhaust vents. All the extras they found to jam inside of the Bax made it one-of-a-kind. The Bax is a TRN ultimate flagship. Same as the ISN EST50 is the ISN’s TOTL flagship. Both IEMs sport dual Sonion EST drivers and offer 10mm woofers. Now some would argue some companies TOTL isn’t the same as other companies TOTL flagships? Meaning for one there is a huge price discrepancy. Take for example the $1,699.99 Sony IER-Z1R. We are going to compare the IER-Z1R next, but just as the Bax is only $312.88 and the Sony is $1,699.99. So? Are they even comparable? Are we really comparing apples and oranges? Due to concentrating on performing a realistic sound response and tonal character, yes in-fact they are...........all three........totally comparable. So to start the EST50 offers a way more involved bass. In-fact, normally I think of the Bax as offering phenomenal bass, and it does. But the difference here is on focus. Where bass is not the true focus of what the Bax is doing. Also just for the record...........just because an IEM has bass focus does’t mean it’s all bass. That would be like going to a bakery restaurant and only eating bread. Everyone knows the bakery restaurant has focus on bread, that is why the bread is great there. But when you sit down for a meal, you have a range of food which makes the meal complete; IEMs are the same way. So just as the bakery has wonderful bread due to focus, the EST50 wins out on the Bax bass due to bass technicalities. Yep, that is correct, the bass is more real with the EST50. It is the expansive mid-range that we go to the Bax for. Where the bass is there, it’s just not as fully catered to. Like I said in my Bax review, it’s just ever so slightly non-polished bass. The Bax has the same personality as the H40, yet even bigger sounding and more vibrant! So, there is a small level of detail with-in the sound elements which offers a loop-hole for both the IER-Z1R and the EST50 to drive a truck through. Think of outer sound shapes and inner detail. Now don’t get me wrong, in many ways I feel the Bax is superior to both the IER-Z1R and the EST50. It’s just that the IER-Z1R fills in the Bax’s sketches, just as the EST50 is also filling in details the Bax glosses over. As far as efficiency, the Bax and EST50 are just about equal.


The IER-Z1R $1,699.99 universal IEM vs the ISN EST50 $459.00 universal IEM:

Flagship 2DD+1BA Hybrid:
Since the time Sony released the IER-Z1R way back in February of 2019, I’ve come to view it in a slightly different light. In 2019 it was innovative and forward walking, arriving somehow from off in the future? And while I still view it as innovative, I’ve come to realize a few things. Number one that it’s actually very conservative in nature. The way it sounds is very classical and correct. It’s like visiting a library, with walls of dusty books telling tales of the past. Those stories are of trueness and the way things should be. The technical ability of the IER-Z1R is special, not only’s my lone reference point. A point that simply goes to show how it’s done. Amazingly I’ve only heard 50 more new IEMs since getting the IER-Z1R……still I approach the IER-Z1R different now. First off the IER-Z1R doesn’t have the same pace as the EST50. Where the bass is heavier with the EST50 and along with that comes a groove, and sway. There is a low bass shelf that is prolonged and consistent that shows-up, not present in the IER-Z1R. Probably the best part of this single comparison is I was almost worried it would be a mistake comparing an over 3X priced TOTL Flagship, against a 1/3 priced TOTL Flagship? But it actually totally surprised me. I thought they would be distant relatives when in fact they are brothers. I mean even memory had me guessing way different. But side-by-sides have a special magic, the rubber meets the road in these instances. There was slightly better separation in the highs, but truthfully I thought prior that the IER-Z1R would have been way brighter?

There is better imaging and tighter focus of elements across the board with the IER-Z1R. A perfect example of what you get for you diminishing return audio dollar; 10% improvement. The wild part is it almost seemed like the ISN EST50 knew what it was up against and dialed up its sound just for the occasion? Lol. Of course the EST50 bass is heavier, but it’s a novelty in form and execution. The Sonys are way, way harder to drive, and that’s the thing the EST50 will (by this single aspect) offer correct bass from a phone, where the IER-Z1R will be foggy. Still when driven right the IER-Z1R has better treble positioning and offers better brightness of individual instruments up top. All to be expected. Amazingly the end-result here is that the two were very close with the overall vibe and presence being the same.Their size of replay very much equal! Really in so many way you come to this same shared sound signature, looking for exactly the same overall sound. It that respect the EST50 and IER-Z1R are speaking the same language. While the IER-Z1R beats the Bax totally in detail, the IER-Z1R comes much closer in detail to the EST50. Of course they are not the same, but closer in tone and ability than I would have ever guessed before this match? To bring this whole comparison back around to the beginning, the EST50 is offering a wild bass, when in direct contrast the IER-Z1R has great bass, though it is less sub-bass enabled, letting it become more conservative and stuffy in the end.


The EarSonics ONYX $561.00 universal IEM vs ISN EST50 $459.00 universal IEM:

1 DD+3BA Hybrid:
The EarSonics ONYX is perfect for rock too. With its dynamic driver adding bass and the 3 BAs doing the midrange and treble foot work, it actually seemed hard to beat. Note too, the price is very close being the same as recently the ONYX went on sale for $463.35. In so many ways this is the direct battle. First off the EST50 is way smaller and lower in weight, which goes a long way to offer a better fit. I will start with using the Walkman WM1Z.

Once in place the ONYX is slightly more difficult to drive. But what's shocking was how the ONYX showed the same imaging yet from a blacker background, maybe the metal-build? Normally you would think this single feature would be good, but it left the impression of the EST50 being more effortless in display. There was more EST50 musical information in the midrange, where the ONYX had more sculpted imaging coming from further away. The bass was actually more with the EST50, where surprisingly the ONYX bass came-off slightly subtle and more reserved......still both are bass enthusiast IEMs.

Probably for most uses these two could be counted as equal, though they are so close that a guess had to be made where the EST50 volume had to be lowered to equal to the ONYX? Though a stand-out feature was the treble in the EST50, showing a style of harmonic richness that fully outdid the ONYX treble. Where the EST50 was a warmer, more detailed treble, the ONYX was showing a slightly brighter rendition of treble except it was thin and not as fleshed-out. Taking both over to the TA desktop continues do provide further direct differences. The ONYX contrast is only a feature, meaning the softer more detailed EST50 element-edges may be what is wanted? It’s kind of like the ONYX is showing less instrument flesh, but more dynamic energy. Stuff is presented with a wider contrast, yet also less connected than the EST50. I hate to say this but the EST50 is slightly more detailed and smooth out of the TA. Where the ONYX happens to broadcast a simpler yet more intense version of the same song. Simpler as each musical element is more separated. The ONYX ends up more the quintessential Hybrid sound. The Hybrid separation may be what you want? The EST50 ends up with lower bass.......robust bass yet more filled in? It is still a Hybrid, but bypasses the pitfalls of existing as a Hybrid. The ONYX also does show more steel-like timbre, where the EST50 does everything in its power to hide such timbre-artifacts. Still the ONYX has to be loved. I mean, what else is doing exactly what the ONYX is doing now? (the EST50).

Look at the ONYX reviews, for Gods sake? In a far-out way they are complementary, only because they are the same but offering a completely different departure in treble and imaging. Both are entertaining, but I view the ONYX as more primal and brutal where the EST50 offers a smoother response despite all the extra bass found. The ONYX is really the monster but not because of more bass, it’s the monster due to it’s contrast and robustness. Does that make an IEM better? Not in this case. They ONYX is straight whisky to the EST50’s champagne. You can get drunk on both, but the champagne is slower. Really, truly, in the end I can’t rate one as better, as each is special, offering a slightly different view. Though if you concentrate on treble finesse and character………..well? I named this review “finessed” for a specific reason.


We learned all about the ISN EST50. A view of ISN spreading their wings and following their dreams. Is it an IEM for everyone? No. Does the ISN EST50 own a special (one-of-a-kind) plot of real estate? Yes……my gosh, yes! Such a place I promise you, you have never been to before. Upon arriving on Bass Island you will find exotic charms only found at this single location. Such a brew is heavy and intoxicating. Your ideas of sound reproduction may be challenged, even coerced, yet you will like it! Maybe? While the ISN EST50 may not be the best single IEM you own, it could be? It’s a personal judgment call if this style of fun is the fun you want to play everyday 24/7. Still there would be no stoping you if this was your choice. The Rock-n-Roll chops that it regularly provides take you to a special place.............far from home. It’s questionable if there is even a way home after this visit? The EST50's build and look is absolutely beautiful. Such swirls and sparklers offer never-ending amusement. The fit is fantastic, the S8 cable is in-fact 100%, the real deal. $459 is a lot of money, yet if you end up falling in love with the EST50, you can keep it forever. If you are into this sound and want to pay for this style of reproduction, ISN has you covered, they have included a piece of art, that just so happens to also play music. What I learned doing this review is that ISN are fully into it, they are obsessed with IEMs. They must be having fun, because I’m having fun? They are a boutique brand that offers a one-of-a kind style of playback. A mid-fi offering that doesn’t know it’s mid-fi.

Disclaimer: These thoughts and ideas are of one individual, your results may vary.

Equipment Used:
Sony WM1Z Walkman DAP MrWalkman Firmware 4.4mm/3.5mm
Sony WM1A Walkman DAP MrWalkman Firmware 4.4mm/3.5mm
Sony TA-ZH1ES DAC/AMP Firmware 1.03
Electra Glide Audio Reference Glide-Reference Standard "Fatboy" Power Cord
Sony Walkman Cradle BCR-NWH10
AudioQuest Carbon USB
Apple iPod
Last edited:
Thank-you. The playback subtlety and finesse did open my eyes, almost like a Head-Fi inside a Head-Fi. A group of highly devoted listeners curious with what ISN comes up with! I hope to review the H50 soon, glad you’re into it! Cheers!
Need a legend X side by side 😏
So true, I wish I did have that IEM model to side-by-side. It would be a good question for someone who has tried them both!


New Head-Fier
Pros: Well-executed Highs, Relaxed midrange tuning, Fit and Build
Cons: Coloured Sound and Prominent Bass may not be for everyone


Disclaimer: This review set was graciously lent to me by a friend from his personal collection and the review is written of my own accord. This set was purchased by him from Penon Audio at full price. If this has helped you, do check out our website for more!

ISN is still a relatively obscure brand, with its most successful model being the ISN H40 Hybrid IEMs. The EST50 is supposedly their latest flagship set to continue the path that the H40s have forged. I have yet to try the H40s, and my only experience with an IEM from ISN is their D02 single dynamic driver earphones which I found to be rather mediocre. Many have mentioned the EST50’s change in sound with burn-in. I personally cannot confirm if this is true as the set I borrowed had >100 hours of usage on it. Without wasting any more time, let’s see if the EST50 is a worthy flagship and if it is capable of competing in the increasingly saturated electrostatic tribrid market.

Accessories and Build Quality (Score: 8.0/10)

For a flagship IEM, the EST50 came with rather minimal accessories. Nevertheless, they are of rather good quality so I wouldn’t be too critical. Included is an ISN S8 cable, which is an OCC Silver-plated Cable. It is available for purchase separately on the Penon Audio website for about US$32.50. Upon purchase, you are free to select what termination you would like for the cable, either 3.5mm single-ended or 2.5mm/4.4mm balanced.

The build quality of the EST50 is excellent. It’s what is expected of it as a flagship. The shell is made with quality resin, and the faceplate has a gorgeous wood grain pattern. The 2-pin socket is nicely flushed and can take many other third-party upgrade cables as well. My only “gripe” with the overall design is the ISN logo on the faceplate looks a little tacky but don’t let me stop you from vibing with it.

Fit (Score: 9.0/10)

The stem of the EST50 is on the wider side, but still slimmer than that of the Moondrop Blessing 2. The stock tips are 2 sets of silicone tips with different bore widths, which I swapped out for my own tips. Wide-bore tips like the JVC Spiral Dots fit my ears brilliantly on the EST50 and also has the best effects on tuning out of all the tips I tried. I will elaborate more on my experience with the Spiral Dot tips in the sound section.

The shape of the shell is very well-contoured and offers a near custom-like feel. I can’t speak for everyone but it fit my below-average sized ears perfectly.

Sound (Score: 8.9/10)


Frequency Response Graph of the ISN EST50

  • Lotoo Paw S1
  • Hiby R5
Music listened to
  • Chicago Symphony Orchestra – Beethoven Symphony 7
  • Boston Symphony Orchestra – The Nutcracker Suite
  • The Vamps – Cherry Blossom
  • Stevie Wonder – In the Key of Life
  • Bastille – All This Bad Blood
  • The Lumineers
  • Børns – Blue Madonna
  • McFly
  • Avicii
  • Coldplay
  • Fun.
  • Family Company

The ISN EST50 has a downward sloping sound signature. It shamelessly rocks a powerful low end with a deep extension. The warm tuning gives a rather coloured sound, which won’t yield the most accurate tonality or analytical sound. I found the bass a little overly pronounced for my tastes and a little too blunt for an IEM in this price range. Personally, I would have preferred a faster bass response to provide some balance for the bass presence. This is especially so when listening to Pop/EDM tracks where the bass can become borderline overpowering almost to the extent of boomy.


Fortunately, things got much better moving into the mids and highs. As expected looking at the frequency response, the vocals and upper mids are a little held back and rather relaxed in energy levels. The balance was a little off in my opinion but those who would want a more laid back tuning would love how the mids are presented.

Switching to wide-bored tips helped a lot and made it very much more enjoyable. My tip of choice was the JVC Spiral Dots and it worked wonders for me. It cut back on the midbass bloom and lifted part of the veil over the mids. My impressions of the mids after the tip change is mostly positive. The mids were never too forward, vocals were very nicely bodied yet crisp. Upper mids are tame in an enjoyable manner, without compromising on detail retrieval.

The separation of musical layers was very nicely done, proving the EST50’s technical prowess.


The highs on the EST50 are no slouch. As expected of a good electrostatic driver implementation, the treble extension is impressive and expansive, giving a very nice sense of space. Instruments like castanets, cymbals and jingles have that added dimension to their timbre, enabling them to come to life. There are no sibilant peaks or weird timbre/tonality issues here. Natural, controlled, yet very good with microdetails.


Nice Imaging and width of the soundstage. The tuning of the EST50 is a little reminiscent of the Thieaudio Legacy 5, but with much more refinement in the bass, which was the bottleneck of the L5 in my opinion. That said, I still feel there is room for improvement in the lower end of the EST50.

Bass quantity is a little too much for my preference, and I tend to not enjoy downward sloping signatures too much as I prefer more energy and presence in the vocals. The bass gets a little satiating to listen to after a while. The colour injected into the sound due to the way the bass and lower mids are tuned can be a little overly unnatural for purists to tolerate as well.

Nevertheless, there is something addictive in the mids and highs that give the EST50s their own X-Factor. I’m confident that there would be fans of this set with its tuning. Just perhaps not too much of a fan given my library and tastes.



Coming into this review, I had limited experiences with ISN IEMs and I could not help but wonder if they were ready for flagship competent enough to compete in the already competitive tribrid market. It’s safe to say I wasn’t let down and this can be considered a good tribrid implementation with a niche but well-executed tuning. That said, I did have my gripes with the bass and overall tuning and tonality.

At the end of the day. if the EST50’s are your cup of tea, they may well be worth the investment and no doubt be a joy to listen to.

Overall Grade: B+​

Click HERE for our grading list for earphones


Headphoneus Supremus
ISN EST50 the rich and the bold
Pros: 2 pin semi custom all resin ergonomic shells utilizing some of the best drivers in the industry for sound. 10mm liquid silicone dynamic+1 sonion BA for mids+1 knowles BA for treble+ 2x Sonion EST drivers for ultra highs. Muscially tuned and refined from bass to treble the EST50 is all about getting the best out of your music. Easy to drive. Very comfortable with a minium 26dbs of passive isolation. Made for eclectic music lovers as it has bass full bodied mids and extended EST treble. Not so picky of sources. Scales nicely with better cables. Nice new pouch.
Cons: Minimum accessories pack which comes with only two sets of tips and a standard SPC ISN S8 cable. Your better cables are highly recommended to bring out the best in the EST50. Absolutely requires a full burn in for the dynamic and EST drivers.
ISN is a brand that was introduced by Penon audio which initially started with more affordable earphone cables on Penon web site. My first IEM cable I bought from Penon actually was an ISN cable, I believe it was the old ISN C16 which is still to this day one of the most unique copper cables in the market that is only on Penon web site.
ISN C16 shown with EST50
Then they started to make earphones and I think the community is very aware of the ISN H40 which to this day is one of the most successful releases for ISN. With great success comes the responsibility of advancing what was set. However the type of sound the H40 was and still is one of the best value hybrid earphones in the market. To truly do one better, ISN is gonna have to step up.

So how does ISN advance the H40 design? They had to go tribrid and utilize some of the best drivers in the industry and that is how you one up the H40. However it is not all about just adding drivers it has to do with that musical tuning of the H40 the reason why folks gravitated toward that sound. The good news here is they actually were aiming for much higher end sound in the EST50 with the same pedigree as the H40 sound tuning. So what happens when you throw in two highly regarded Sonion ESTs and a unique potent 10mm dynamic with the inclusion of a single Sonion BA for mids and a Knowles BA for treble.
Before getting into this review standard disclaimers. I was provided with a review sample from ISN and you can purchase a set for you here. Their website here.

What makes the personal audio hobby interesting is that there are always new advancements in the types of drivers produced that promise advancements in 2 channel stereo for our ears. Just the sheer variety of dynamic driver types, BAs types and now Sonion has made some waves with their relatively newer Electrostatic drivers. Hybrids are so yesterday. It is all about the tribrids nowadays. EST drivers are interesting as they seem to be utilized for just the upper treble portion of a earphone design. I was told Electrostatics have some difficulty with lower treble frequencies so the upper trebles seems to be where they are utilized the most and this is the case with most earphones that utilize EST drivers. EST sound is a bit different than your standard BA for upper treble designs which is best described as the perfect sound sauce for the treble region. What I mean by that is ESTs innate ability to add air dimensional ques with precision and nuanced details to treble notes is uncanny. There is a reason why some of the highest end earphones in the industry are all gravitating to use the Sonion electrostatic driver for their designs.
What's included.
The shells, the ISN S8 cable which is your standard SPC 8 core variety of cable the good news is this cable matches up well with the sonic ability of the EST50. Even better you can choose single ended or balanced termination when ordering a set of EST50s The bad news is I wasn't expecting a treasure trove of tips but 2 sets? Again it is not all bad as the green silicone tips they included matches up well with the EST50 here again. I suppose as long as they include something that works well. The new green case they included is a magnetic lid clamshell case which reminds me of the old Sony cases that was included with the old XBA earphones. Nice newly designed case is much better than the generic zip up rectangular cases they used to provide. To be honest I am a bit disappointed with the accessories here but that is not the reason you are reading this review.
Drivers are the foundational aspect of the sound design but then it comes down to the type of tuning each manufacturer decides to grace these drivers with and then you get the final product. It has dawned on me that ISN does not go for a ruler flat type of sound but more so the type of tuning that allows for full music immersion. Some may call it analogue in quality, old timers will love the tuning that ISN has bestowed on the EST50 as the tuning incorporates a lot of what makes them older studio recordings shine.

But then utilizing some of the best drivers available for the cost means these have the technical ability to get you into your music no matter what you listen to.
Sound tuning is best described as a balanced L shaped frequency design with a modest 6 dbs or so of pinna gain with the most emphasis toward the lower end especially sub bass. This particular design and the choice of drivers here has a lot to do with how well received last years H40 was and still is. It is clearly an attempt at doing one better than the class favorite and here we have a continuation of that classic musical design of the H40. Now utilizing premium drivers.
It is what you would expect. More of everything that counts the EST50 is a no holds barred full bodied musical sound signature that has everything to do with enjoying everything about our music. It is what I would imagine a true successor to the H40 can only be. Heralded as their flagship model the ISN EST50 has upgraded more than just the sound tuning.

Sound analysis was done using my DAPs Fiio M15, Shanling M6pro, M5s, M3s,Ibasso DX160, Sony ZX300, Cayin N5ii, Pioneer XDP-30R, Ibasso PB3 and IFI BL for amping.
A word about burn in.
Truth is some earphones don’t do a damn thing with burn in and some do. The EST50 clearly does. Out of the box you're greeted with an overly warm sound and a bass end you best be prepared for. Lets just say I thought the bass driver was broken. I have heard flabby thud one note bass before but I was not expecting it on the EST50. But that is what you're greeted with but alas burn in will and does changes everything about the sound on the EST50. You better believe the silicone dynamic and the EST drivers need a good burn in. Not so much the BAs. You can tell how the sound is going to be but no way does the open box experience result in what you're actually gonna get at the end. So I highly advise folks to run some music at moderate to lower volumes through the EST50 for a week and then take a listen.
EST50 sounds.
So it was apparent to me even on open listen that this tuning was going for a bold sound and has nothing to do with an analytical approach. There is nothing on the sound that is neutral or flat. You don’t buy a mid fi category tribrid with 3 different types of drivers for the design to analyze your music, you buy it so you can enjoy your music to take full advantage of the three driver types. This is what these are all about. Big bold musical, richly dynamic and very immersive, The EST50 is clearly the successor to the H40. These are optimal ear speakers to listen to your eclectic music collection. It is personal audio at its finest and I am glad that ISN has approached the EST50 with this angle.

EST50 has a touch of warmth to its tonality as did the H40. I would put the sound of the EST50 into a technically balanced presentation with an underlying design of musically dynamic in the category of sound profiles. No point in the tuning are they overly analytical but at the same time these are clearly showing advancements due to the premium drivers ISN is using. I will do a more complete comparison with the older H40 toward the bottom of the review but for now just know these are clearly an update on what made the H40 so good. You get a similar stage expansion but each part of the sound design gets a dedicated upgrade and refinements..
Earphones have this or it doesn't. The EST50 could be called EST50 the Bold. Cus bold sound is what is going on with the EST50, be warned however that the EST drivers don't really fully open up till you get that burn in to take effect. Once it does you get the traits of what EST drivers do. A potent deep reaching bass and a lush rich mids presentation. That dimensional quality to the treble is full on and has excellent smooth quality extended trebles that inject some air with pinpoint presence to the trebles, this in turn results in some of the best quality treble in the price range. By the nature of the design the lower trebles are not as accentuated as a lot of chifi earphones and hence the EST50 are an easy listen yet treble details abound with a type of sound you can get lost in for hours with no fatigue.

Electrostatic treble, when utilized well, adds a sense of space for treble notes with better nuanced details than your standard BA treble or a well implemented dynamic treble. Sounds decidedly more natural vs something like a piezoelectric ceramic tweeter, with the ability to extend extremely well injecting air and articulation to treble notes to the upper mid portions of the sound profile. A well implemented EST can be the difference between dull treble to sparkly extended crisp dimensional treble that completes a tonal quality to the fullest. EST50s has a refined treble end as it is utilizing a single Knowles BA to do lower treble notes and two ESTs for the ultra highs. This combination of ability and natural tuning for the highs make all the difference. Treble sounds absolutely superb with the right sparkle and shimmer on the EST50 using 3 higher end dedicated speakers just for the region. This allows the EST50 to have a higher level of treble many earphones are lacking in.
The transition
To the mid bands are seamless and here is where the older H40 shares some similarities to the new EST50. Mids have always been great on the H40 and here we see an uptick for the mids ability due to an upgraded Sonion BA doing the mids duties. Sonion BAs have a tendency to have a richer tonal character and this is clearly evident even on open listen. A single bore of the EST50 is dedicated for the mid bands hence mids are full on. There is no mistaking that tonal quality of this Sonion BA added a full rich sound. Folks that love their mids to have good, body, weight/ substance and fullness in quality, the EST50 mid bands are right up there with the best the designers have ever made. Folks that have heard how good mids are for the Penons own Spheres, Orbs, Globes, and Volts will immediately recognize the tonality and presence of the mids. The EST50 has nothing to do with a thin skinny sound. How many times have you read a review of an all BA set sound description where mids take the crown and the treble and bass are a step back in quantity and quality. On the EST50 you're essentially getting it all. There is nothing holding it back. You're gonna get the full monty experience for sound.

You can’t call an earphone a flagship level with anything held back is my point. The sound is full on with the EST50 and you're going to appreciate not just the balancing act to get that sound right but just how capable each portion of the sound bands truly are in the EST50.

Technicalities on the EST50 are supreme and has great layering to instrument placing/ imaging in the sound field you're listening to. This aspect clearly shows the refinements for the mids that their previous earphones showed aspects of but is not quite as good as it is on the EST50. Mids are more than just the best aspect of the EST50 but then if you have basslines for your music you listen to that is where things get really interesting.
A potent BASS
Bass has always been a foundational aspect of ISN design. All their earphones have bass emphasis but here we get a highly specialized 10mm liquid silicone diaphragm for bass on the EST50. This isn’t your garden variety bass we are talking about here. Bass has a presence, roundness, a supreme elasticity, authoritative rumble and reach. Bass is the foundation for a lot of music I listen to, be it rock and metal to jazz to hiphop and EDM. And I can tell you. Bass is not an afterthought or does it play a supporting role in the sound design for the EST50. It is featured.
ISN managed to squeeze bass potency, presence and ability all through one of the 3 bores to your ears. This bass takes that musical bass of the H40 into a different level. Again burn in is highly recommended for the dynamic driver to really strut its stuff. The difference in tone from out of box to where I have the EST50 bass drivers firing off now is remarkable and completely different. The quality seems to get better and better as they age. Here we have bass presence to the likes of some of the best bass performers I can think of for hybrid/ tribrid designs.

Mid bass has a bit less emphasis vs the sub bass but both are represented extremely well for your music. I can say if you're the type that purposefully are looking for a weak limp bass tuned IEM then you should most definitely look elsewhere. Again nothing is neutral on the EST50. Bass has clear coloration and a boost to it that makes your music come alive with a lower note that has some extreme qualities.
This rounded bass has a mid and sub bass presence with a steady increase of sub bass to about 12dbs. That is not really extreme per se but since the dedicated dynamic here seems to excel at bass, it sounds more emphasized than the graph shows. I own plenty of earphones with what looks like similar or more bass emphasis but the bass end of the EST50 makes you take notice.

Its tonality is absolute. Defined bass notes of the EST50 has a rawness and power to the bass notes that is akin to an amplified dedicated woofer. It does sound more like speaker bass and that is amazing coming from earphone bass that is only 10mm in size. Texture of the subs here is nothing short of remarkable with a tighter yet beefy bass note from mid bass and sub bass authority. Sub bass decay is some of the most realistic I have heard and is comparable to the best I own, even my IER Z1R. However with bass authority comes the complaints that there might be too much bass emphasis. I don’t think so, the sound design has a large enough stage to encompass a stout bass end and here in the EST50 the bass dynamic is clearly a bass specialist. Bass punch for bass punch I bet the EST50 punches a bit harder. Rumbles a bit more than yours. Sub bass sustain with a slower decay and sounds like you have dedicated subs in your EST50 and you can most certainly look at it that way. Bass is a part of the EST50 sound design so you should clearly know this before buying a set. You're not going to hear a brawny bass for every type of genre you're listening to. It will come down to how much bass your music has in the recording. With that bass authority and good passive isolation of the EST50s I find them perfect for outdoor activities. Last thing you want when out and about is a limp noodle bass end from your tribrid. I am happy to report the EST50 has a good healthy amount of bass but nothing that is going to ruin your orchestral scores or vocal tracks but you will get a nice ear lobe rumble when listening to EDM and hiphop.
In the end
The EST50 is a compelling product. I can clearly tell what the designers of the EST50 are going for. It is more than just one aspect of the design that shine on the EST50. You are really getting all of it. They are more than just catering to bass enthusiasts it is catering to mids fans and capped off with a complete treble that has high quality and extension capped off by a large immersive stage. It is personal audio with a no holds barred sound signature. Yes it is a colored tuning but I bet your earphones will sound boring after hearing the EST50s. The big question is. Are the EST50s a true upgrade on the previous H40? Not only are they a true upgrade. These will be an upgrade to many earphones that are hovering around this price range. Especially if you love your bold full bodied sound. There really aren’t too many choices for earphones in this price range that does exactly what the EST50 can do. That saying you can have your cake and eat it too. This is essentially what the EST50 is. It has great treble, it has great mids, it has great bass, it has a great stage. What more do you want? As always, thanks for taking the time to read and happy listening.
Here on this section I would like to put on here what it is that the EST50 actually does better than the H40 cus many will ask.
VS the H40
First off, even by today's standards the H40 is a supreme value. One of the best hybrids your hard earned money can buy at the price. Both earphones have excellent wider stages, both are balanced well for their given sound designs but when you really start listening to each part of the sound designs that is where the differences start to appear. The biggest being the mids and how they are presented. H40 is not a thin sounding earphone but compared to the EST50 mids there is a drop off in micro details, layering and sound separation in the mids. EST50 has the better depth, a richer tone with better timbre of instruments. There is no question the quality of the mid bands sees a jump in quality here. Hence the mids portray with more realism with better atmosphere and air, so the higher end mids Sonion BA is clearly showing what it can do. Bass especially sub bass has more authority and out rumbles the old H40. Mid bass sounds tighter and more defined even though both have comparatively similar impact for bass. Treble is also more advanced in the EST50 as you would expect. Better treble articulation and detail. More dimensional sounding with better extension and air the EST50 sounds more complete for treble and again it isn’t like the H40 treble is lacking but it is clearly outclassed by the Knowles BA and two Sonion EST drivers.

So from what I am describing it is a more refined experience all around but that is what you would expect.

Vs Penon Globe

I did this comparison against the Globe due to Globe owners wanting me to shed some light vs the two. These two earphones have a lot in common. Sound balancing for one and both are using similar Sonion BAs for mids with similar tonal and dynamic qualities.

You can call the EST50 an evolution of the Globe sound signature. Globes utilize two bores out the nozzle the EST50 has 3. Just by design the EST50 shows better separation of the 3 zones of sound. Both do vocals amazingly well but since treble is completely separated from the mids, the mid bands have better overall definition as a result. Both sound very dynamic and full on. Globes has a touch more upper treble emphasis but it is the EST50 that has the better treble extension and sounds more complete for treble with a better sense of air due to the EST upper treble sounds more rounded for treble notes.

On graph it shows that the Globes might have more bass emphasis but it is actually the EST50 seem to have a slight edge in impact, bass extension and texture.Globe bass end sound more like full bodied earphone bass. The EST50s are more approaching speaker like bass. EST50 simply has more authority, a bit more in the way of quantity and most definitely an upgrade in quality.

EST50 shows a slight uptick in imaging and sound separation, an enhanced Globe technically. The EST50 and the Penon Globes are closer in tonality, stage and ability vs the H40 but the EST50 does have the upper hand against the Globe when it comes to micro details, a more dimensional extended treble and shows a bit more authority for sub bass performance with an increase of texture.

EST50 vs Volts
I consider the EST50 Volts younger brother. They share some striking similarities in sound balancing using similar type of drivers too. Volts are like the grown up version of the EST50 sound design. Both earphones leaning more toward musicality, fullness and immersive qualities of sound balancing.

Both earphones use a 3 bore design so more similarities there but the Volt has more refinements for its sound design, a wider deeper stage vs the EST50. To be fair it isnt like the EST50 has a weak or closed off stage. It is just that these higher end IEMS do put focus on stage and depth of the sound. In fact EST50s has a remarkable surround like stage due to how musical they sound that is in no way claustrophobic or closed in sounding. EST50 stage is actually pretty excellent about par with the ISN H40 actually.

The difference are in how the drivers were utilized, On the volts the mids are using both Sonion BAs, the EST50 uses a single Sonion BA for the mids and one knowles for treble. The Volt is using the quad ESTs for treble. It is known EST drivers struggle a bit in the lower trebles so by default EST drivers are more about extension, air, dimensional qualities to your treble.
Since the EST50 has a dedicated BA doing lower treble it was tuned to be proficient there but the sound tuning has the treble not being so prominent which again is a fine balancing act here. Where the EST50 stand out from the Volt is its bass presence. Volt has some good bass but to my ears is a bit more even handed with the balancing.

EST50 bass is not so much more emphasized but this silicone dynamic being used is most definitely catered toward bass fans. Sub bass especially has emphasis to the likes of some of the best sub bass performers I can think of including my IER Z1R. Mids strike a very similar tonality and forward presence but the difference again is a bit like how they are compared to the Tansio Mirai LAND and how those were tuned with two BAs doing mids. Volts has better imaging and detail in the mids due to both Sonion BAs being used there and mids has more of an airy quality as the stage is more enhanced on the Volts as well. Treble presence and extension is the most identical between the two with Volts exhibiting a bit more airy quality to upper treble notes. Volts shows a more tonally balanced and basically more refinements and again more technical yet uses a very similar sound balancing as the EST50.

Essentially your getting 90% of the Volts performance at almost half the cost. Laws of diminishing return is happening here. EST50 with a upgraded cable comes even closer to the Volt. Volt with an upgraded cable takes off into a different stratosphere in sonics however so if I was comparing both units with upgraded cables it would not be a fair match but as they are the EST50 comes strikingly closer to the Volt in performance and is also able to show some uniqueness due to the bass driver that is again Stout in what it does. For folks that have never owned the Volts the EST50 will surprise in many ways if you end up getting the EST50 your really getting a bit of the Volt magic with them. Both are supremely musical in their presentations. If you can imagine what the EST50 would sound like with even better refinements that is in fact what the volts are.

As similar as the EST50 are to the sound balancing to the volts they clearly have their own sound and tuning involved at a bit over half the cost of the volt the EST50 I can say is got some good value to what your getting. Especially if your a bass fan.
Cables match ups.
Stock cable is the exact same cable that was included on the ISN H40. The ISN S8 which is a classic ISN cable and one that matches up well with both the H40 and the EST50s however. No way is this basic cable going to optimize the EST50 to its full ability. Here are some cables suggestions that can really bring up the strengths of the EST50 and make the sound even better than what was provided.

First off, don't be afraid of using pure silver on the EST50. Due to the moderate treble emphasis and ample bass emphasis of the EST50. Pure silver matches up extremely well with the EST50. Of course not all silver cables are the same. So the sound comparisons using these cables are against the stock ISN S8 cables. As good as the stock cable is. EST50 sounds better with higher end cables.
First we have the Penon Mix. I did a review here. The Mix turns out to be a great match for the EST50 as it is half crystal copper and half pure silver. This cable enhancing ability is very well balanced in what it does and I noticed an uptick in clarity due to the pure silver while maintaining the great mids and bass presence due to the copper aspects. You also get a benefit of a more expanded stage when using the Mix. The Mixs highly resolving ability for a moderate sum is ideal for well balanced tribrids like the EST50. Better resolving with excellent dynamics and an expanded stage is what you get on the EST50.

Next is the ISN AG8, review shown here.
When I mentioned not all silver cables are the same. Take a look at this bad boy. One of the very best unique pure silver cables in the market. Unlike a lot of pure silver cables that thin out a sound. The sheer physical makeup of the thicker cored AG8 matches up with the EST50 as it adds an element of a thicker sound vs your standard pure silver cables. The AG8 enhances everything about the EST50 with a tighter bass note, a cleaner sound and the widest stage possible. Silver does enhance detail and you get that with the EST50. The AG8 was the very first cable I threw on the EST80 and it will be a tough choice if I want to keep the AG8 or the Mix on the EST50 once I am done with my review. Good news there is I can always switch up when I want to. Choices are always a good thing.

Last but not least A flagship earphone deserves a flagship cable
ISN Solar. I did a review for here
Now we are talking true higher end level sonics. Solar enhances with even a richer tonal character due to the gold plated cores. Enhances stage, not quite like the AG8 but more like the Mix and adds a more rounded note definition for trebles. Bass sees a slight uptick in rumble and imaging is enhanced, treble is smoothed out but clearly defined. The Solar costs almost as much as the EST50 but when you combine these two. It is like a long lost puppy that found their way home. The match up is undeniable. Solar enhances that musicality with an enhanced richness, better instrument separation and adds a more tangible air to the sonics that none of the other cables can do. You want maximum EST50. You gotta pay to play. I would say with the inclusion of the Solar on the EST50 I can see how the EST50 will put up a fight with your more expensive in ears. The EST50 is clearly enhanced and takes a liking to more better cables.
Last edited:
Great review. :L3000: Is the texture and speed of the guitars and the speed of the bass good for metal music? Does the soundstage have depth or is it just wide? How does this compare to EJ07m, which also uses Sonion BA for the mids, if you've listened to it. Thanks!
  • Like
Reactions: Dsnuts
Never heard the EJ07m. I grew up listening to metal and rock music so that is one of the music genres I test out when I do my reviews. The mids and lower treble is done with BAs so guitars have absolute speed. No issues there, one of the great aspects of the EST50 is that is has great depth and height of sound so your not gonna be left with a thin note weight for music in general if that is what your worried about. The bass dynamic is fantastic and sound more like speaker bass. It keeps up with speed metal just fine. If you want a beefy sound to your metal music I would try out the EST50. I think you will like. The only catch on the EST50 is that they need burn in for the dynamic driver on them.
Any experience with the Legend X compared to this?