Reviewer at hxosplus
Not shy of bass
Pros: + Sub-bass extension
+ High quality bass
+ Dynamic and impactful
+ Engaging mid-range
+ Smooth treble
+ Resolving and refined
+ Spacious soundstage
+ Easy to drive
+ Comfortable
+ High quality cable
+ Carrying case
+ Excellent build quality
Cons: - Not suitable for critical listening
- Bass could use more control and speed
- Bulky ear-shells
- No modular or second balanced cable
This is a review of the ISN Audio EST50 which retails for $449 and you can buy it from Penon Audio.


The ISN EST50 is a hybrid earphone that uses 2 Sonion Electrostatic drivers for the ultra-high frequencies, 1BA Knowles for high frequencies, 1BA Sonion for the mids and a 10mm dynamic for the bass.

Appearance and fit

The lightweight ear-shells have a design that is pretty much identical to that of the ISN H30. They feature an anatomical shape and are made from a skin friendly resin compound. They are a little bulky when compared to single driver earphones but the mildly extending sound tube and the semi-custom design helps a lot with the fit which is stable and comfortable even after prolonged time of use while they effectively block environmental noise. The faceplate has a beautiful wood grain pattern with the ISN logo engraved at the center of it and is available in two colors, stabilized wood orange and green. Build quality is simply excellent.


The ISN EST50 comes with two sets of silicone ear-tips in three sizes each, two pairs of memory foam ear-tips, a cleaning brush, a shirt clip and a premium looking, high quality, hard carrying case with a magnetic lid. The presentation box is a little bare bones and not as luxurious as someone would have expected.


The ISN EST50 features a 1.2m detachable cable with 2-pin 0.78mm connectors and you have the option to order it with either 3.5mm, 2.5mm or 4.4mm termination plugs. The truth is that at this price point a modular cable would be a better and more competitive offering. Thus said, the braided cable is of good quality, it is super lightweight and soft without microphonic noise and it doesn’t get tangled.

Technical performance

The ISN EST50 is rated at 18Ω/100dB so it doesn’t have much requirements for power but it really responds well to higher quality gear. I have mainly used the iBasso DC04PRO, the Cayin RU7 the FiiO M11S and Penon Tail. As per usual practice the ISN EST50 was left playing music for about 100 hours before listening evaluation.

Audio performance

Fun and exciting, the ISN EST50 has a tuning with a tasteful bass emphasis without letting down the rest of the frequencies. The dynamic driver can reach deep enough to the lowest notes, rewarding the listener with a subwoofer experience. The sub-bass isn’t overpowering so the mid-range and treble stay clear and defined enough. The bass is emphasized, especially in the upper part of it, as a result is not that well suited for critical listening. Timpani will sound more overpowering than they should and double basses or cello are rendered slightly out of tune. Of course there is much more than classical and the tuning of the ISN EST50 low-end is perfect for listening to rock, metal, electronic and other kinds of similar music where a hefty, but not dominating, bass is desirable and adds plenty of excitement. The ISN EST50 is very dynamic and impactful, the bass is visceral and weighty although not that well controlled. Definition and layering are satisfying but the bass is slightly on the slow and relaxed side.

The mid-range is superb, tonally balanced and accurate, articulated, well defined and crystal clear. The timbre is natural and realistic with plenty of harmonic variety, everything sounds lifelike and engaging. Voices, female especially, are heavenly good. The ISN EST50 has a musical and present mid-range which sounds good with everything. The transition to the treble is smooth without any fatiguing upper-mids emphasis, making the ISN EST50 the ideal choice for people with sensitivity to this particular area.

The treble is easy to the ear with an aristocratic politeness but without lacking in extension and excitement. The EST50 is not the most brilliant or sparkling sounding earphone but still there is plenty of light and enough energy to keep things moving and well contrasted to the low-end so the sound is not excessively warm or dark. The Sonion drivers add a great portion of resolution and refinement, the treble is of the highest quality, it is full bodied and decays in a relaxed manner. Tonality is quite accurate so all instruments sound realistic without artificiality while electronic tunes are not piercing or fatiguing.

The five drivers are really well integrated so the overall sound signature is very cohesive without any weird tonal shifts or audible frequency discontinuities. The ISN EST50 is quite open sounding with a solid center image and excellent stereophonic panning. The truth is that it doesn’t sound too holographic or proportionally layered but it offers sharp imaging and plenty of air around the performers.

The ISN EST50 wouldn’t be my first choice for critical listening to classical music but it gave really great moments and much enjoyment with classic rock and metal bands like Guns N’ Roses.

Vs Dunu EST 112

The Dunu EST 112 has a rather balanced tuning with more neutrality in the bass, great presence of the mid-range and a treble that is definitely more emphasized, sharp and less forgiving than the ISN EST50. If the ISN EST50 represents the casual and fun oriented earphone then the Dunu EST 112 is it’s reference and critical sounding counterpart. The bass is more imposing and impactful, the larger driver moves more air while it manages to stay fast, tight and controlled albeit not as visceral and full bodied as in the EST50. The mid-range is lusher and warmer in the ISN EST50, a little more musical, with a weightier texture and less biting in the upper mid-range. The treble is smoother and more forgiving in the ISN EST50 while maintaining excellent resolution and refinement. Equally refined and resolving is also the Dunu EST 112 in the higher frequencies but it is slightly sharper, brighter and more energetic sounding than the EST50 with faster transient response. Two good sounding earphones of the mid-range category with slightly different sound profiles to cater for individual listening habits.


The ISN EST50 has a deliberately casual tuning with plenty of well realized bass, present mid-range, well defined treble and great technicalities so it is well suited for listening to all kinds of music as long as there are no critical requirements. It is musical, exciting, engaging and responds well to upstream gear. Well made and very comfortable, it is highly recommended but it would be a much better value if it had a modular cable.

(The review sample was kindly provided free of charge in exchange for an honest review)
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1000+ Head-Fier
So you like Bass huh?
Pros: Terrific bass-driven sound & admirable technical performance
Cons: Treble-sensitive listeners may need to watch their volume level
How much bass is enough?

This age old question has divided mankind for centuries, since the days when stone-age audiophiles would fiercely debate the properties of drums made from Sabretooth Tiger pelts vs Mammoth hides.

How much bass you require will be influenced by a variety of factors.

Your preferred musical genres for instance, your average listening volume, which digital audio player you use, and even the geometry of your ear canals may alter your lower-frequency preferences.

Or it may come down to mood – at times you may prefer to feel instead of hear the music.

ISN Audio have created an IEM for such occasions… the EST50s.


Earlier this year I was very impressed by Penon’s Impacts, and they must’ve felt similarly about my review because without asking they sent along a pair of complimentary ISN EST50s to review. I’d barely heard of ISN to that point, and was dimly aware they sold cables but had to google the EST50s just to see what they were!

Of course I immediately felt a pang of guilt – you see one of the Impacts’ few drawbacks is their absence of a dynamic driver, so although their bass is excellent by BA standards, it remains BA bass nonetheless. Having commented on this, could Penon have sent the EST50s to prove they do indeed sell IEMs with bountiful bass slam?? Remind me to complain they aren’t expensive enough to see what happens next…


The ISN EST50s are USD $449 tribrid IEMs containing a single DD for bass, one Sonion BA for mids, one Knowles BA for highs and two Sonion ESTs for ultra-highs. It’s a delightfully minimalist configuration that keeps shell sizes small whilst giving you that juicy EST goodness.

They’re bundled with ISN’s S8, a relatively thin 8 wire silver-plated OCC cable with 2pin connectors. A multi-plug version isn’t offered so instead you’ll choose between 4.4mm, 2.5mm or 3.5mm terminations. The IEMs also come with an 18 month warranty.

The EST50 shells are vented so pressure build-up isn’t an issue, and the first thing you’ll notice is how incredibly shapely they are. ISN have attempted to imitate a Custom-IEM form factor in a universal body as much as possible here, and the end result is uncommonly comfortable– so much so they deserve special praise for how easily I forget their presence in my ears, coupled with the excellent isolation their deep fit provides.



The EST50s arrive in a fairly small & very light cardboard box with a leather carry case, leather accessories case, three sets of eartips, shirt clip & IEM cleaning tool, and the aftermentioned ISN S8 cable & leather cable holder.

Many audiophiles pay quite a bit of attention to packaging and “unboxing experiences”, and after spending thousands of dollars on a luxury product that’s perfectly understandable. Obviously the EST50s lack that sort of pricetag, making a more modest collection of accessories acceptable.

I fall into the camp of preferring minimalist packaging that’s less costly to ship so the EST50 ensemble doesn’t bother me, particularly as it lends assurance that as much of the purchase price has been devoted to the earphone as possible. However some might argue the quality of the box & case leave room for improvement.


Sound Impressions​

Upon listening to the EST50s for the first time you’ll be immediately struck by their deep, resonating bass presence. It is more heavily biased towards sub rather than midbass and thus is especially satisfying for electronic music, of which I have a particular fondness.

Having tested them with Spinfit W1 tips via a Cayin N8ii DAP (solid state mode with P+ enabled) using local files stored on a Micron i400 micro-SD card, I found bass is very much north of neutral, and you’ll feel as well as hear that pounding bass slam!

Bass quantity isn’t quite as extreme as FatFreq’s more expensive Maestro SE which remain the most over-the-top set of IEM bass cannons I’ve heard, but it isn’t too far away either. There is ample rumble, slam and impact down low, which will serve any bass-dominant album or genre extremely well. Bass texture could be improved, but remains satisfying.

The really good news is the EST50s have been tuned extremely tastefully, demonstrating a controlled aggressiveness that generates plenty of excitement without excessive fatigue. You’ll hear all that bass without it overpowering the midrange, nor is this the kind of slow or bloated bass we can experience with budget DD IEMs.

In fact the EST50s’ dynamic driver is responsive enough to do fast-paced music with busy passages justice, without ever creating coherency issues with those faster BAs & ESTs. Indeed coherency is one of the EST50’s great strengths, with all five drivers combining harmoniously.

There’s enough bass & treble to qualify the tuning as tastefully V-shaped, with the midrange avoiding any recession or dryness common to poorly tuned V-shape IEMs. Both female & male vocals demonstrate plenty of presence, but may not quite convey the refinement we see from IEMs worth thousands of dollars. To be fair, that sort of smoothness would probably impede the visceral rawness that makes the EST50s such fun in the first place.

Treble performance is excellent thanks to the presence of those two ESTs, with plenty of sparkle and commendable resolution without the need to hunt for detail. I did feel nuances were presented slightly more effortlessly by IEMs with vastly higher pricetags, but the relative difference was quite small. Indeed the EST50’s treble prominence has proven to be fantastic for classical music, not something I expected from IEMs with basshead DNA.

Technical Performance​

With regard to technicalities the EST50s are capable, but perhaps not exceptional beyond the constraints of their cost. Dynamics are superb, perhaps aided by their superb coherency. Soundstage is wide but not spectacularly so, but isn’t the deepest with layering a notch down from multi-thousand dollar IEMs, and imaging is solid without calling attention to itself. This is where swapping to a more expensive cable helps.

Resolution is well above that of budget IEMs, perhaps only a very small step below earphones worth thousands of dollars, and this difference rarely asserts itself without actively straining to pick up minute changes.

Overall the EST50s straddle a wonderful line between being brash enough to evoke a feeling of raucousness, without being so raw they fail to perform well with most genres. In terms of nitpicks, I wouldn’t call them cold or sterile but a touch more lower midrange warmth would occasionally be nice for vocals, and if you listen at high volumes you may find their treble prominence excessive. I’d also love an even wider & deeper soundstage without having to pay more for an upgraded cable.


IEM Comparisons​

Penon 10th Anniversary 2xDD, 2xBA, 2xEST (USD $499)

It’s only natural to start here given my recent 10th Anniversary review.

Unquestionably the best IEM all-rounders I’ve heard under $1000, the 10th Anniversaries are more relaxed & refined than the EST50s, with a more polite presentation that’s less bombastic and excitable. Physically they’re slightly larger and not quite as comfortable, though the difference in comfort wouldn’t discourage me from using them.

10th Anniversary bass is certainly enough when called for but lacks the over-the-top quantity & slam of the EST50s, and is biased towards midbass rather than sub instead. 10th Anniversary treble is also not as prominent, resulting in them possessing a much milder V-shaped signature. They also have a significantly richer, smoother midrange, but I find the EST50s to have slightly better coherency.

The EST50s are significantly more upfront with a feeling of being closer to the performers, and this gives the 10th Anniversary the impression of having a wider soundstage though perhaps not quite as deep.

The 10th Anniversary remain the better all-rounder choice, but simply aren’t as fun or exciting as the EST50s, particularly for bass-dominant genres like electronic music.


Dunu SA6 MK2 – 6x BA (USD $579)

I was loaned the SA6 MK2 by my friend Neweymatt and was surprised to find they’re much larger than the EST50s despite containing only 6 BA drivers. They certainly stick out quite far but are comfortable regardless, being very sculpted to the ear like the EST50s, and thanks to their larger shells isolate even better.

Being BA-only, the SA6 MK2s bass is something of a surprise being extremely impressive by BA standards… but lacking the added texture, slam & punch of the EST50s. The SA6 MK2s midrange is little dry, and although they demonstrate the pleasurable sensation of speed & precision achieved by omitting a DD, that slightly plasticky BA texture is present. Nor can the SA6 MK2s emulate the EST50s effortless resolution, perhaps due to the lack of EST drivers. Dynamics are also poorer.

The SA6 MK2s do possess a wider stage than the EST50s, but it is not as deep. They’re more easy listening IEMs that are very well balanced, and it’s unfortunate a comparison to the EST50s paints them as a poor choice because they’re actually quite good if you accept those BA-only shortcomings.


Kiwi Ears Quartet – 2xDD, 2xBA (USD $109)

The Quartets are surprisingly large for their driver count, but very sculpted & comfortable with build quality rarely seen at this price. They contain a pair of tuning switches, which I leave in the OFF position for pleasing results.

Most immediately apparent is how much of a step down their bass is from the EST50s, both in terms of quantity and quality. With less lower midrange emphasis they produce a dryer sound, that is tonally much flatter & more subdued, not helped by poorer dynamics. Their treble is also whispy, lacking body.

The Quartets’ resolution is very disappointing, but their one advantage is a slightly wider soundstage than the EST50s, although it has almost no depth to speak of. Essentially the Quartets are outclassed rather badly.


7hz Legato – 2x DD (USD $109)

My friend o0genesis0o loaned me the Legatos which are certainly unique in their aluminium construction, being quite possibly the most slippery IEMs I’ve ever struggled to handle without dropping. They’re also physically large & heavy, but lack the ear-hugging contours of the SA6 MK2s or Quartets.

With their double DD’s the Legatos have also been touted as basshed IEMs, and indeed their bass quantity is north of neutral – greater than that of the Quartets, but lacking the quality of slam & impact of the EST50s, nor is bass quantity as high. Overall the Legatos are less V-shaped, being more polite and smooth but less exciting as a result.

Unfortunately the Legatos also suffer from poor dynamics, inferior resolution & soundstage depth compared with the EST50s, and though their treble is more substantial than the Quartets’ they lack the sheen & shimmer of the EST50s’ EST drivers.

Truthear x Crinacle Zero – 2x DD (USD $49)

As you might expect from a double DD IEM the Truthear Zeros are quite large, but very light. Their shells aren’t sculpted to ear geometry at all, so eartip choice is crucial for a comfortable fit. Physically they’re reminiscent of Fir Audio’s Frontier Series containing the XE6 – not uncomfortable, but perhaps lacking the rounded contours of other IEMs.

Requiring a humungous amount of power – almost double that of the EST50s to reach similar volume, the Zeros feature a very wide but flat stage, a somewhat thin & recessed midrange with fairly neutral bass biased towards sub. This creates the feeling of being seated a long way back from the performers, with a somewhat uninvolving sound.

The Zeros have a very flat treble presentation that sounds one-note in its’ simplicity, with a lack of weight behind those higher notes. Though the stage is very large, it feels artificially stretched in much the same way Sennheiser’s IE900 does to me. The Zeros are a relaxed & laidback IEM, the very antithesis of the EST50s.


Cable Comparisons​

Do cables make a difference? Of course they do, but I’m sure you knew that already.

There’s absolutely nothing wrong with the EST50 stock cable, in fact the ISN S8 is excellent value for what it is. However there’s distinct advantages to opting for something different, and I’ve never been one to pass up an excuse to roll cables so let’s give it a try and see where it leads us!

ISN S8 (USD $32.50)

The EST50 stock cable uses 8 wires of silver-plated OCC and is quite bright, accentuating treble and imaging. It’s also extremely light & comfortable, even by 4 wire standards.

The S8 doesn’t enhance stage dimensions quite as much as other cables, and its’ added treble sparkle & upper midrange accentuation contributes to the EST50s exciting presentation. This could potentially lead to fatigue if you’re very treble sensitive, in which case a copper cable may prove be a better choice.

Penon CS819 (USD $49)

The 10th Anniversary stock cable is similar to the ISN S8, with 4 of its’ 8 silver-plated wires replaced with OCC copper instead. Surprisingly on the EST50s this leads to better separation, with more lower midrange presence creating a sense of fullness.

Note weight is also improved, with vocals in particular having more substance behind them. However dynamics & treble sparkle are diminished compared with the ISN S8, but this could potentially result in less fatigue.

NiceHCK BlackSoul (USD $50)

This extremely comfortable 2 wire ‘5 element alloy’ cable creates a wide but flat stage, rolling off treble significantly to create a much smoother sound, but I do find bass is more muted compared with the stock cable and imaging also seems negatively affected.

A good option for anyone who finds the EST50s treble too hot & dynamic, though I don’t care for this pairing as I’d rather not having the EST50s excitement tamed.

Penon Vocal (USD $69)

This 4 wire silver-plated OCC copper & gold foil cable is sure to get you noticed in a crowd, and is a nice visual match for the flame-inspired EST50 faceplates.

As the name suggests Vocal pushes vocals forward and enhances midrange clarity & note weight, balancing out the EST50s natural V-shaped sound. Everything becomes smoother, calming the excitement to create a more mature sounding presentation.

A perfect low-cost pairing to turn the EST50s into more capable all-rounders.

Penon Obsidian (USD $149)

This heavier-than-expected 4 wire OCC copper & gold plated copper cable takes the improved refinement of the Vocal cable & kicks it up a notch. This is a testament to the importance of cable synergy – previously I’d found the Obsidian disappointing on both the Penon Impacts & 10th Anniversary, but it pairs with the EST50s extremely well.

It even manages to widen the EST50s soundstage, something it didn’t seem to accomplish with the Impacts. The lower midrange also feels more crunchy & visceral, with even better separation than the Vocal cable creating a greater feeling of cleanness & control. Bass seems slightly less impactful, but I don’t mind the trade-off.

Penon Leo Plus (USD $249)

The 8 wire gold-silver-palladium alloy Leo Plus again demonstrates it’s ability to accentuate treble, widen the stage, improve resolution & make things like cymbal splashes stand out even more.

However dynamics seem diminished, and bass doesn’t quite hit as hard. Although this creates a sound less likely to fatigue I’m not overly fond of the pairing.

Effect Audio Ares S 8 wire (USD $279)

With 8 thick wires of OCC copper the Ares S boosts the EST50s lower frequencies as it did with the 10thAnniversary, dynamics are also improved as are resolution & imaging.

This is an ideal choice in the unlikely event you fail to find the EST50s visceral & punchy enough, although shifting the focus towards the bottom end even more may leave the EST50s feeling like a blunt instrument on music genres requiring more delicacy.

Liquid Links Martini (USD $349)

Another hefty 8 wire cable, of gold plated copper & palladium plated silver, the Martini boasts the same superb dynamics, soundstage & resolution improvements of the Ares S.

However the Martini emphasises the upper midrange rather than the lower frequencies of the Ares S, leading to slightly improved articulation coupled with a more polite overall signature, tastefully smoothing out the treble in the process.

Liquid Links Venom (USD $1089)

Despite possessing only 2 ‘quinary alloy’ wires, Venom emulates the improvements to soundstage & dynamics of the 8 wire cables previously mentioned, and adds even better resolution, separation and a blacker background.

Though unquestionably the first choice in this cable shootout for improving the EST50s technical performance, Venom’s natural V-shaped inclination towards boosting sub bass & treble emphasises the EST50s existing strengths in a way that doesn’t feel as satisfying as expected – instead inflecting a somewhat clinical tonality.



Returning to the earlier question of how much bass is enough, ISN have provided an answer your ears deserve to hear.

There is ample weight and power to be savoured here without suffocating the rest of the frequency spectrum. Even the midrange, so often an afterthought in V-shaped signatures is instead rendered with commendable weight and presence.

Make no mistake however, the EST50s want you to have a good time. Delivering a fun, bouncy sound is their priority at the expense of refinement, though you’ll still get most of the resolution & technical performance of far more expensive IEMs.

Could ISN have delivered more effortless detail, an even larger soundstage and more pinpoint imaging whilst maintaining the same bass-driven flavour? Perhaps by adding more BA & EST drivers, but then the EST50s would be physically larger as would the price.

Instead they struck an excellent balance – but is that why since arriving simultaneously the EST50s have enjoyed far more of my ear time than Penon’s 10th Anniversary?

I’m not sure being smaller & slightly more coherent explains it – no, there’s something compellingly satisfying about the way the EST50s deliver those glorious bass drops which you’ll understand when you hear them.


Headphoneus Supremus
ISN EST50 a subwoofer experience
Pros: Subwoofer like bass
Clear sound with full body to the low end
Smooth mids and treble without any concerning peaks
Overall detailed while staying fatigue free
Nice design in different colour styles
Above average soundstage
Did I mention bass to die for? While not ruining the rest of the frequencies.
Cons: Big shell
Cable and accessories could have been better for the price
Bass may be to much for some
Treble while detailed might not have enough energy for some
ISN EST50 a subwoofer experience


The EST50 is my second IEM from ISN, I bought it with my own money. All impressions are my own subjective thoughts after using them for over many months, and I have no association with ISN writing this. This is also a very subjective hobby where everything from experience, anatomy or age will affect what we hear. Also keep in mind that it is easy to use bold words when talking about differences, while it may be perceived as a small change for you. I can describe something as natural sounding, while at the same time I believe we can never get 100% close to a live performance.

About me and my gear used for the review

My audio preference is neutral with sub and mid bass boost, mids can be forward but not too much. I can also handle some extra treble if it is not excessive. I am a believer in having different tuned IEMs for different genres or moods instead of chasing the single perfect one.
Main music genres I listen to are Metal, Electronica, Jazz, Indy rock/metal, R&B, Pop. I am a music lover, and can also listen to almost all the genres out there. I have been into music gear since the mid 90s, gifted some big speakers at an early age. Then moved more and more into headphones with the Koss Porta Pro and a Sony Discman and Minidisc.

I have tried playing many instruments over the years from piano to sax and have a feel for what's a natural tone, but not the biggest patience in learning to play. My wife has also played many instruments from string and wind instruments and also piano.

My current standard in Headphones is ZMF Verite and Beyerdynamic T1 G2.

My current standard in IEMs is AüR Audio Neon Pro and Penon Serial. The Neon Pro has 10 BAs, and has a near perfect tonality for me. The Penon Serial also has a near perfect tonality for me, that is more relaxing and organic sounding with its triple DD configuration.
Both of them have sound signatures that I can listen to all types of music with.

Gear used in the main rig is Topping E70 DAC together with the Topping A90 Discrete headphone Amp. I also have a Schiit Lokuis I can swap in if I want to do a little analogue EQ.
I have also used the Feliks Audio Echo, one of the more silent OTL amps.

Portable gear used during the review: Truthear SHIO, Tempotec Sonata HD II , Hiby R6 III, Hiby R3 Pro Saber 2022, Quidelix 5k DAC/AMP.

I have a good range of cables from ISN, DUNU, Penon, NiceHCK, XINHS and some others.


ISN Audio

ISN Audio is a brand under Penon, they have a wide range of both cables and IEMs.
When you read around on the forums about ISN, you will notice that people say that ISN is IEMs with a bold and solid low end. While this has some truth, both the latest H30 and H50 have a more balanced sound.

ISN D01 6mm DLC DD
ISN D02 10mm Carbon Chrystal DD
ISN D10 9mm DD
ISN H30 9.2mm Beryllium Frosted DD Bass + 2 BAs mids and highs
ISN H40 9.2mm DD + 1 BAs Mids + 2 BAs Highs
ISN H50 10mm Composite DD + 2BAs Mids + 2BAs Highs
ISN EST50 10mm DD + 1 BA Mids + 1 BA Highs+ 2 EST Ultra Highs

They also have cables from cheaper models to their top model the ISN Solar.


So what is the ISN EST50

The EST50 is a tribrid, meaning it has 3 different types of driver technologies inside.
The low end is handled by the 10mm Dynamic Driver. Mids are handled by a Sonion BA. Highs is handled by a Knowles BA.

This alone could have been an IEM, but here there are also 2 EST(Electrostatic) Drivers to create some extra upper treble or air as it is called.

They are built with the same resin and form factor as most Penon and ISN models, and you can choose from the normal color or the stabilized Wood Orange as I have.

The shell is quite big and has a nice ergonomic form factor, I can use them for hours without any ear pain. The length of the nozzle is above average, so for me it gives a perfect seal with most tips.

ISN Audio EST50 Flagship 2 EST + 2 BA+ 1 Dynamic Driver Hybrid 2Pin 0.78mm HiFi Audiophile IEMS


Brand:ISN Audio
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
Connector: 2Pin 0.78mm
Plug: 3.5mm audio , 2.5mm balanced , 4.4mm balanced
Cable length: 1.2M

18 months warranty


Package and accessories

The packaging has this blue chrome finish that looks quite nice, the inside has foam keeping the IEMs in place and the overall presentation looks good.

There are not that many accessories, you get 1 set of S, M and L silicon tips together with S and M foam(not sure about the size but the foams are small and not usable for me). The included silicone tips are actually one of my favorite tips, a good balance between openness and giving some tightness in the low end.

The included cable is the ISN S8, this is a cheap but good cable to get you going. It is an OCC cable with silver plating. The included cable does nothing wrong, but I have changed it out for a more premium cable. Soundwise the S8 is ok, but it feels a little cheap compared to the S4 they also sell.

The blue ISN Case is a good one, with a magnetic clip to hold it together. It is not very big and you can maybe fit a small dongle together with ES50 inside it.

There is nothing wrong with what is included, while some extra tips or a better cable would have been appreciated.


How does the EST50 sound like?

First impressions were different from what I hear now, this is one of the sets that has changed the most with burn in for me. At first it was more V shaped than L in its sound signature, the EST drivers did have a certain edge to them.

I would call the EST50 a bold, smooth and fun IEM. The bass is elevated and especially sub bass, mids are more neutral in approach, treble detailed and fairly neutral.
This is a sound signature that is called L-shaped, the star of the show is the bass that is elevated while the mids and treble are in harmony with each other. The mids are neutral in amount, and it increases slowly up into the upper mids so it is never fatiguing for me.

This reminds me of when you have some good non fatiguing speakers paired with a big subwoofer. And the subwoofer is cranked up a little to give some extra low end, it is very addictive and fun.

That is basically what the EST50 is, it is not correct if you ask many. But one thing is for sure, it is very fun.

Music genres are also a thing here, not everything will sound perfect with a sound signature like this. At the same time the EST50 is good at not pushing out bass when it is not supposed to, since the most boosted area is the sub frequencies. It works with most of my music library, while the genre I prefer the most with the EST50 is electronica.

Going to use the ranges here in review:

First off, what is Timbre?
From the Wikipedia:
The Acoustical Society of America (ASA) Acoustical Terminology definition 12.09 of timbre describes it as "that attribute of auditory sensation which enables a listener to judge that two nonidentical sounds, similarly presented and having the same loudness and pitch, are dissimilar", adding, "Timbre depends primarily upon the frequency spectrum, although it also depends upon the sound pressure and the temporal characteristics of the sound"

First minutes of trying a new set of gear, what I always listen to is how natural and musical it sounds. Much of this goes down to how I perceive the Timbre.

The timbre of the EST50 is a little weird. The mids and treble has a timbre that is clean,modern ,fast and also a little relaxed. While the low end has a more organic forward sound. This does melt together well enough so I don't think about it when listening to music. I do believe this is due to the bass being handled by a dynamic driver and the mids and trebles being handled by BAs. Two different technologies. BAs from my testing, are always more modern and clean sounding compared to Dynamic Drivers. But I know there are exceptions out there where it melt better together than with EST50.



Gear and cable synergies

The sense of scaling is clearly here and they deserve a higher end AMP or DAP. While even a small dongle will give you good sound, the amount of finesse with higher end gear does push it higher.

I do prefer a neutral to slightly warm sounding source, the Topping E70 and A90D is one of those combos. Often people just think about numbers when getting Topping gear, this DAC and AMP combo is one of those combos that has a sound that's a very neutral with small hint analogue touch. It is a great combination and pushes the EST50 capabilities over a standard dongle.

As for dongle pairing the Tempotec Sonata HD MKII is more musical sounding compared to the Truthear SHIO. While the SHIO gives out the most detailed and fullest sound with the EST50.

Hiby R6 III does also sound great, I have no need for using the MSEB equalizer.

Also a little mention of pairing with the Feliks Audio Echo OTL amp. The lows goes from being sub bass oriented to having more mid bass, while the mids and treble gets thicker and darker sounding. Quite a fun combo to use for slower metal genres, or to get a more rave-like sound in electronica.

Got recommended the Penon Mix Cable, and I agree on the very good synergies. While I still prefer going for a good Silver Plated Cable, I don't feel the need for the extra treble with the Mix. Even the stock cable ISN S8 does nothing wrong, while a thicker and better cable is well appreciated and deserving of the EST50.

Also I just recently got the Penon Vocal cable, this cable does push forward the mids and perhaps the lower treble. Here we talk about a perfect combination of IEM and cable, this is clearly my favorite combo. Even though I am not a fan of the design.


Details, Soundstage and Imaging

Details on the EST50 are on par with Hybrids or Tribrids around the price, nothing spectacular but nothing wrong either. Imaging is quite spot on and very 3D, where I can pick apart where sounds are appearing with ease. I have also tested playing some First Person Shooter games, very easy to pick up where shots or footsteps are coming from. While the more relaxing treble and increased bass takes away some accuracy for gaming. I would say this is a perfect set for story games, as the sub bass does give you the cinema feel of a subwoofer.

Soundstage is like sitting a few rows back from a performance. Depth is slightly forward out from the head while sounds coming from the sides are above the average width.


Strive by Amber Rubarth

This whole album is a recording that has a wide and large soundstage. Strive is a very nice track to test deltail, imaging and soundstage.

EST50 is larger than most IEMs I have listened to here, the soundstage is more wide sounding than having large depth. Even with my ZMF Verite that has an above average soundstage the stage here is more wide than deep.

Very good layering with good 3D capability of where the sound cues come from. Here I do notice much of the small details, I would have believed it was lost in the EST50 due to relaxed treble nature. The drumming and clapping is quite spectacular with some very nice impact that you truly feel, very fun to turn up the volume on this one.


Thriller by Michael Jackson

Brilliant track to test everything from bass, mids, treble, soundstage, dynamic range and detail.

First thing that happened here is I have my whole body moving, the whole track is a masterpiece on EST50. If the ZMF Verite is the standard here for me, I do lack a little amount of energy in the treble. Looking at the imaging ability, EST50 does it well. The sound cues are all over, you get a good sense of being inside the recording. Michael Jackson's voice appears slightly in front of you instead of directly in the head. While the sound cues to the sides are rather far out.


City Nights by Allan Holdsworth

Jazz Fusion, the electric guitar and drums here is fast and technical. Some sets with too much energy in the Upper Mids can be quite tiresome on this track, while darker sets will sound dull. Again the EST50 hits this just perfect, never fatiguing or boring. It just sounds right. The amount of detail is very impressive, if the mid bass had been elevated to much some of the detail would have been lost here. It just sounds very balanced to my ears, with great detail.


Bass, the star of the show?

I appreciate a punchy low end with good extension, and at times I do want it elevated over what is neutral. I can also enjoy the true bass head experience, but then it comes back to what type of music I listen to and my mood.

The amount of bass here is bold, more in the sub bass range than mid bass. The bass shelf starts in the lowest part of the mids, then rises slowly almost linearly.

I was very curious when getting the EST50 how the bass shelf would look, Tony(Akros) got his set after me. We had a chat and he sent me the measurements, it shows what I heard. The bass just grows upwards until the lowest Sub Bass, while not boosting the mid bass too much. Some well known bass IEMs increase the bass early, then flat out around 100Hz. Making you want more Sub Bass as the “Mid Bass” takes the show. I prefer the EST50 approach as it goes better with more music genres, this also gives less bleed into the mids.


Angel by Massive Attack

Very good track to see how good it handles sub bass slam and how deep the low end goes. This is goosebump material if you like bass, the control and amount is perfect. The whole track is rendered excellent, from the vocal to the distorted guitar. The intensity that builds up at the end feels effortless and never feels congested, and the last bass kicks at the end can rattle your brain.


Something About Us (Love Theme from Interstella) by Daft Punk

Who doesn't like some Daft Punk, could have picked lots of tracks from them. But I am very fond of this in particular, there's a nice drum kick around 50HZ and one at 150Hz making the beat. You are supposed to hear the difference and again the EST50 renders this perfect, the balance between the Sub kick and Bass Kick is in harmony here. Not one sticks out. Nothing to complain about.

So What by Miles Davis

Blasphemy, how can I listen to such a classic jazz piece with a basshead IEM? That's the thing, the overall tuning does not push the low end too much forward when it is not asked for. The double bass is the one thing to listen for here, a lot of nuance is his plucking of the strings. The double bass should never be the main thing as plucking of a double bass will always be less loud than the cymbals, sax and trumpet. Here is what I said before, the bass is there not trying to steal the show. EST50 shows the bass notes, while I could have preferred some more detail in the plucking.



Very often with elevated bass the mids get overshadowed by the low end. Or get a bass bleed for that matter. Since many said on Head-Fi that ISN is more V shaped brand than its brother Penon, I was happy to get the EST50 and hear clear natural mids. Perhaps a little gentle compared to a more forward mid centric sound of Penon Serial.

This approach being more neutral in mid energy makes vocals and instruments never become harsh or too intense. Male voice has some extra fullness due to the bass, something I prefer for male voices.

Going up into the Mid frequency I can hear some slight uneven energy If I listen to a rising tone, still we do not listen to music like that and it is never hearable through music. The upper mid range or lower treble area has some slightly boosted energy compared to the mids before.


Show You The Way by Thundercat

The whole album is a gem, this track is picked due to having a wide range of vocal presentations. As I mentioned before the male voice has some extra fullness, this is a track I personally do not like if you listen to a reference neutral set. I probably had this song on repeat for 10 times while trying to write here, I find the whole presentation close to perfect.

I can find the bass beat to be a little over the top when I increase the volume, but at the same time it's fun and addicting. What impressed me the most is how well the EST50 does the vocals here, if you own the EST50 take a listen and be impressed.


Songs from the North by Swallow The Sun

Swallow the Sun usually makes melodic doom metal, disc 2 on this release is not really Metal. It is focusing more on a relaxed listening with melodic acoustic music. This track has both instruments, male and female voice.

The EST50 makes the drums and guitar sound crisp. Not forward in the mix, well balanced together with both the vocalists. Both the low Mids and Mids are well balanced here, while still having enough energy in the upper mids not making it lifeless. I personally prefer some extra presence in the upper mid range so the EST50 is very close to my preference here.

If I would be very critical, I could have liked the vocals a small amount more forward here.


Mexican Margarita by Jacob Guerevitsch

Introduced to me by my friend Akros.
Jacob is a Danish artist who plays Spanish guitar. Lots of detail, dynamic range and complexity. I prefer to put Mexican Margarita in this part of the review, since most of the sounds here are in the midrange.

Wow, just wow. This is so dynamic and impressive, I prefer this piece on sets with a dynamic driver for its low end. It just makes the drumming sound more real, and the guitar is very crisp with lots of detail.

What impresses most here is how natural and good it all sounds, there is some extra fullness than what I would call a reference sound. But I Like it this way more, it is intoxicating.


Treble and Air

Treble is a little relaxed to me while still keeping itself detailed, there is a nice anti sibilance dip from 5-8KHz. Treble sensitive people should be safe. Unless I can handle brighter signatures better than others, I do love Beyerdynamic headphones after all.

The amount of treble extension is quite good, the presence of the upper harmonics is there. While some may be wanting more when listening to classical music, I am not the perfect judge for classical.

The treble is not meant to be the star of the show with EST50, I bet this is something of the tuning philosophy of the maker for the IEM. It is detailed enough so it does not sound veiled or dark, while also not stealing the show. If the treble were more forward the overall sound would have changed to amore typical V shaped sound. But this does not mean it lacks detail in the treble.


Take Five by The Dave Brubeck Quartet

Perhaps one of the most recognised Jazz pieces out there, even with being recorded back in 1959 it sounds so clear and crisp. Perfect for checking how clean the cymbals and brass is portrayed. There is also some good airyness going on here through the cymbals.

The EST50 portrays more than enough detail while also being relaxing, there some good detail in each cymbal strike. Amount of Air is also clearly present and above what for example the DUNU SA6 can show here.

It is remarkable that the EST50 can be this relaxing while retaining so much detail, I also never feel the bass is overdone ruining the rest.


Humming by Portishead

Another on Head-fi recommended my try this some years ago when I was testing a headphone for how fatiguing the treble is. It has lots of weird elements, and sounds almost trippy. There are lots of unpleasant sounds that are shown if the treble is too forward or harsh.

From testing it on a loop for a long time there is no fatigue, nothing in particular sticks out as a problem area. Also nice hearing how well all the sounds melt together on EST50 without feeling congested.


Towards the Bending of the Light by Yamantaka

Percussion elements here are nice to check how clear and how extended the amount of air is. Again a little above average, well extended but not the sparkle that some are looking for. For me there is no problem as I am not the biggest fan of exaggerated air, at least as long as there is some detail going on.


I do not own any other tribrid for comparison, I will only compare to my reference sets Serial, Neon Pro and the H30.




Penon Serial

The Penon Serial is an IEM with 3 Dynamic Drivers, one for bass, mids and highs. The set is highly recommended by many people. Priced a little lower than EST50, a very musical IEM with great timbre. The Serial is natural, bold and sensual sounding.

If the EST50 are some good speakers with a 12 inch subwoofer that's cranked up, the Serial is more like the big vintage speakers with 12 inch woofers. One clean and modern
sounding with elevated low end, while the other having a more analogue bold sound.

The overall sound and timbre is more modern in EST50, very similar to how it is when comparing a modern Yamaha upright piano to a Kawai. Both are great while one will sound better with some arrangements than the other.

The amount of sub bass is more in quantity with the EST50, the rest of the bass is similar in amount with some extra mid bass in the Serial. As for how the low end resolution is, the EST50 can slightly pick up more nuances in double bass playing. Both have a bass approach that has slower decay compared to for example the Penon FAN 2 or the Dunu SA6.

Mids are more forward in Serial and thicker sounding, vocals are more easy on the ears and relaxing with EST50. Female vocals especially have a more forward and romantic sound with Serial.

Treble detail and resolution is going to the EST50, having also the most treble extension.

Soundstage does seem wider in the EST50, while the Serial wins in how forward it appears. I Do wonder if it is because of the wideness of EST50, making it stand out more than the forward depth.

Both have great timbre, but here I will give it to the Serial as it does sound more true to life.

Can read my whole review over at:


AüR Audio Neon Pro

Neon Pro is a IEM from AüR Audio that has 10 balanced armatures per side, it is my favorite set and my standard in tonality.

When checking a true sub bass track like the Mezzanine you notice some differences here. The amount is more and also looser on the EST50, and it seems to be in more control on Neon Pro. Neon Pro also sounds to me more natural in the decay since EST50 is on the slower side. The upper bass kick hits harder on Neon Pro while the amount is very similar.
The detail in the bass notes is perhaps slightly more detailed on EST50.

The EST50 is more like a stereo speaker setup with a 12 inch open vented subwoofer backing it up that is also turned up some, Neon Pro is more like a high end modern speaker setup with big drivers giving fast and punchy but with elevated low end.

Vocals are very similar, it can appear slightly warmer on EST50 but it is small. When listening to a track with only instruments it is not as easy to differentiate the mids. It is first when entering the upper part of the mids that you notice they are less forward on EST50, this you can also see at FQ measurement of EST50 since it has a gentle Pina Gain. This also makes the EST50 very safe if you're sensitive to upper midrange energy. Neon Pro has a more natural amount of upper mid range and does acoustic music more justice.

Treble is similar in amount, but what's weird is that even with EST50s EST drivers the amount of upper treble is more detailed and forward on Neon Pro. It is also smoother on Neon pro especially in the lower treble. For air I can not really differentiate them, it can be that ISN have not implemented the EST drivers well enough. Or that Neon Pro is just that good.

Overall resolution is good with both, I do put the Neon Pro a good step ahead. I do notice more detail especially in the mids and treble.

Soundstage with the Neon Pro has the same amount of depth to the sides but can also portray more depth in front. Especially on the Amber Rubarth album the sense of space is more vast on Neon Pro, there is more blackness to the background making it seem endless.
There is also very good layering that is above most cheaper sets with both.

Can read my whole review over at:ür-audio-neon-pro.26395/reviews?fbclid=IwAR0d5j87HTND_YR89EdqLIzHIjxXGUvFxHME9jjNo3MsDDx-Uoqfyd_z4to#review-30495



Why the H30, it is also an ISN and the first IEM I got from ISN. It is a hybrid with 1 DD and 2 BAs priced at $129. I use the H30 almost daily at work and it has some similarities to the EST50.

Both have an ergonomic fit with a long nozzle for great isolation and secure fit. The overall shell is much smaller on H30, but I don't think about the size as both are made very ergonomically.

Bass is very well extended on H30, it even rises almost the same. Both increase gradually all the way to the lowest rumble. The big difference here is in the low end, the EST50 has around 12dB increased sub bass while the H30 ends at 5dB. A few at Head-Fi had problems with not hearing the bass with the H30, with a good seal it is very well defined with really good extension. it is just the amount that is on the lean side.

Both have very similar midrange, the H30 vocals and instruments can at times appear slightly more forward and detailed. The mids on EST50 appear smoother and more refined, especially on a few sax or trumpet parts.

Going up into the upper midrange/ lower treble is where it changes. H30 has some extra energy around 5-7k Hz, this can be fatiguing for some depending on how sensitive you are to this range. it is not sibilant, but the energy is clearly forward. EST50 is much more relaxed here in comparison.

Upper treble is well extended on both, the electrostatic drivers do give the EST50 more refinement in the upper range.

Also a note on soundstage. The H30 is really good for its price, but compared to the EST50 it is a step back in size and resolution.



EST50 is a coloured set that is not correct when looking at perfect instrument playback, but a smooth and clean sounding set with a deep subwoofer like experience. It is addictive and makes me smile from ear to ear.

This is not the one IEM to rule them all, but rather the fun set to have in your collection. Not the set for the ones who prefer a neutral amount of bass, if so look somewhere else.

I do recommend it, is it worth its asking price? For me, yes. For others maybe not. If I lost it would I buy it again, without a doubt yes.

Ranking System

1 Very bad or unlistanable
2 Listenable but not good
3 Average
4 Very good
5 Exceptional or having a special sauce

Price can push something up or down half grade.

If I think about electronica music I will give this 4.5 of 5 stars, but for some other genres maybe only 3.5 stars. So in the end 4 star is very adequate.

If you're looking for your audiophile basshead experience, this will maybe be the one for you.

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"Treble while detailed might not have enough energy for some" - sounds like a mission for the Unsilver Silver. Did wonders on the Serials with better prat and better air, extension and sparkle.
Excellent review on this one, on top of the 3 albums as my preferred reference, Brubeck, Massive and Miles...
Good review! I still am not sure how I feel about mine, but I am surprised that we had such different experiences with imaging, it seems really poor at that imo.
Imaging is very personal, heard IEMs that people say is large being small for me. Much if this is due to just our hearing or earcanal being different.

At time of review I rated it pretty good, after tried some really nice staged IEMs now I would have maybe been a little harsher now.


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.


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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
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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!

The SC4 really helped align the whole signature into perfection. I mean it was maybe just me, but I didn’t have such cable when I was writing the review. I view such an addition is crucial in opening up the treble and subduing the bass authority. I obviously liked the EST50 with the stock cable, but somehow it was enhanced further with the SC4 and wide bore tips? So much so that’s it’s now one of my favorites of all time. There was a profound clarity and bounce which opened allowing the true character of the ESTs to shine! IMO


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
I burned mine in past 300 hours before the bass resolved.


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.
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350+ hours on this and I feel now they are burned in. There was a little bit of thickness in the bass note, but it finally resolved....
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Truly excellent review. I'm coming from Aria to OH10 (love) but want a true basshead iem. Damn - I just ordered the Fatfreq Maestro Mini last week and am waiting on it. But the EST50 seems like what I really want. They graph similarly but I think the FFMM has even more bass but lacks the EST drivers and likely won't have the clarity of these. My plan was to get the Empire Ears Bravado mkII next, but the EST50 seems to offer competing overall performance as bass beasts with impressive mids/treble/stage and is over $300 less.

Shame that there's no reviews of the H40, H50 and EST50 on YT. ISN Audio deserve way more attention it seems. I was initially interested in the H50 as I came across them earlier this evening, thanks to a comment on another iem on YT. But I think theres too much upper mids for me there.

This is my first comment and I'm enjoying some of the detailed and passionate reviews here. Looking forward to contributing my thoughts in the future.
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I have the Xenns Up as my bass extension set but was looking for something more.... I have looked at the Fat Freq MM as well as the 7hz Legato this set seems to strike a balance between the two. I do have the Solar cable on my Dethonray Tender's and the AG8 cable on my Serials also the Leo 2 plus on my 7hz Timeless, all of which are excellent cables and enhance the performance of said IEM's. I have been impressed with the quality and value from Penon/ISN so this is looking to be my upgrade on a bass centered set.
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