Knowledge Zenith (KZ) ESX

After reading all the hype and seeing some graphs, i bought an ESX expecting them to be the best KZ yet.



NOPE, major disappointment. mids sound unnatural, treble is mediocre, bass is fun and that's about it.

These are arguably just a worse DQ6S, both have a similar sound signature only ESX is more V shape, DQ6S is more balanced, without the upper mids peaks.

I see absolutely NO reason to buy this when the CRA and DQ6S exist. The CRA has better treble details and similarly deep-bass.

One thing that really concerns me is the appearant differences between the KZ ESX samples sent directly to reviewers, and the ESX units you get from retail.

Those reviewers got an ESX with a much more balanced sound signature, without the huge upper mids spike. The red graph below is Pualwasabii's review sample and the green graph is a retail unit.



Me and Paul use the same mic, our other measurements are consistent with each other (Chu for example)


HBB got his ESX from Linsoul, instead of directly from KZ. His unit matches my ESX unit and like me, he wasn't too impressed.


I spoke with KZ on this matter and was thoroughly assured that my unit was NOT defective, and considering that the channel matching is good on my pair i also didn't think my pair was defective, so why is there so much variance between units?

Has KZ already made a revision? They've done it before. They have changed nozzle filters on the ATE and ZS3, They changed the BAs in the ZS5 after release which then received criticism for sounding too harsh. KZ revisions aren't just numerous, they often make the iem significantly worse than the first batch.

If that isn't the case, could this be just poor QC? and i simply got the unlucky end of the ESX stick? Some people have told me that their ESX purchase was a similarly disappointing experience, but there are others that say ESX is the best KZ ever.

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Before you read this review
Change the eartips to widebores when using newer KZ releases, just please, as stock eartips make the sound boomy and more v-shaped, degrading the sound quality by a lot. Throughout this review I will use Kbear07 as my main eartips, stock eartips are disregarded.


Summary
Most refined KZ so far, fun, safe, detailed, grand, open, dynamic, and organic sounding, a very suitable all-rounder IEM that will suit most music lovers’ taste (except neutral heads). Sound signature is leaning towards a U-Shaped presentation with significant hump around 250 Hz. Making ESX to dig subbass really well while also hitting the listener with slam, texture, weight and punch. Midrange is also excellently tuned, both male and female vocals are properly forward on the soundscape and exhibit accurate tone and lushness (however there are some tracks where the vocals will be 1 step back from the instruments, mainly occurs in heavy bass tracks). Lower treble is excellently tuned, guitars and violins have enough clarity but aren’t artificially sharp like the OG CRA. Upper treble has a dip (yeeessss~) which contributes to its wide soundscape, 3D feel and organic replay. Overtones also aren’t always forced to the listener, and all instruments are always perceived with proper distance on the soundscape (in short, it has a very good imaging/staging). Talking about imaging, soundstage has above average width, average height and above average depth. Speed and dynamics are also excellent and the sound will literally attack you with force whenever the tracks need that grandness and big presence on the soundscape. ESX mainly excels with all western tracks and selected Japanese music.

Disclaimer

• Take my review with a large scoop of salt and always cross reference.
• I like to thank papa KZ/CCA for providing me a review unit of the KZ ESX
• I will analyze the KZ ESX with references to my Dynamic Realist (EDA Blanced) and my most expensive set that I’ve tried so far (Yume Midnight)
• This review will somehow be biased towards my taste in music and my target sound signature.
• As always, since our ears have different shapes and resonances, your mileage may always vary.

Preliminary

• I’ve used the KZ ESX for over 3 weeks with different sources and tips, played different tracks ranging from pop to bossa nova.
• Before listening to ESX, I have taken a half day break of listening to IEMs, this is to make sure that ESX’s sound signature will be fresh and new to my ears.

Equipment

• CX-31993
• Avani (ALC-5686)
• Abigail (CX-31993) “Main Source”
• LG V20
• Xiaomi Mi 4

Thy Frequency Spectrum
Yeap, like Practiphile said ESX is the king of macrodynamics, all notes carry this very thick weight (presence) that makes the instruments exhibit this grand presence on the soundscape, its literally enticing the listener to jam with the music and ignore the microdetails in the music.

Bass: 9.8/10
Subbass digs really really deep (e.g Fresh Static Snow by Porter Robinson, ESX will literally guide you towards the deepest bass part of that track, just indulge and relax, it also rumbles very cleanly throughout the soundscape). There is also this significant presence of the lower pitched instruments on the soundscape, drum kicks and bass guitars feel very physical and real and I can somehow feel them beside me, it’s a bizzare yet a very indulging experience really, I can't explain how I love the bass presentation of ESX. Yes it bleeds in the midrange, but man the presentation is grand, theatre like, tight and textured..I don't know how to explain it anymore please helpm..if I have to really nitpick, bass lacks the snap and it doesn't decay that fast like the EDA Balanced. But overall man..deserve the 9.8, it’s just amazing.

Midrange: 7.5/10
Recessed depending on the track, if the track is somehow bass heavy the mids will be perceived as recessed otherwise it’s pretty forward in most of my tracks. Both male and female vocals are accurate and I can't detect any honk or boxiness to them. However, male vocals are more forward on the soundscape and exhibit more lushness/raspiness compared to female vocals. Female vocals also do not have this lovable sparkol/brightness/cleanliness that DR has so take that into consideration, to be honest it’s kinda like the Tanya vocal presentation but a bit tamed and laid back. Instrument fundamentals has a bit of warm tint to them and isn't as organic sounding like the Tanya, midrange has this warm coloration giving this thick note weight to all instruments where the fundamentals lie between 200-1kHz.

Treble: 9/10
Safe, palatable and harshless, yet isn't dark sounding at all. Treble does not have the edge (which some of KZ IEMs exhibit, e.g EDXU, CRA+, EDA Hires) and sounds very easy to the ears, piano, wind instruments, strings have enough clarity, notes are well nuanced and articulated on the soundscape. The treble presentation lacks the sparkle (gentle upper treble glide like the DR) but it has proper staging and frontal projection of instruments due to the dip at 12 kHz. Making the instruments to be placed 360 degrees around my headspace. Additionally, the dip at 12kHz, also contributes to the lack of bass snap and overtones might not be audible in some tracks (death of cymbals are hard to catch in some tracks). But overall, even if ESX doesn't have the satisfying treble sparkle and clarity that DR has, it still feels complete and not lacking at all like the Tanya which is straight up butchered in the upper treble.

Technicalities

• Driver quality and speed is the same as the EDA Balanced, but unlike EDA Balanced all notes are carried with significant weight and you can somehow feel that some instruments especially bass guitars are in your front (it feels very 3D). Attack is a bit slow compared to EDA Balanced, but decay is almost the same and the drums sticking and changing of rhythm of kickdrums can be heard easily. It isn’t smudging or blurred in any way.
• Soundstage has an excellent width and height, above average depth (wider and taller than Yume, has better depth than Yume Midnight), it’s like you are in a large studio room and the instruments are placed 360 degress within your headspace. It isn’t like the EDA Balanced where you are in a hall (EDA Bal renders reverb and echoes on the soundscape amazingly tbh), but the presentation is much physical/real and there will be sometimes where you will be shocked at how real some lower pitched instruments sound, it’s like the Tanya presentation but on steroids.
• Imaging and staging are excellent, and almost the same as how Yume stages instruments.
• Separation is above average, but it isn’t that well separated like the EDA Balanced, it is much smoother sounding, more cohesive and relaxed sounding. It will make you ignore the details and just enjoy the music “ESX literally embodies the quote written on the box”.
• Microdetails are below average, and reverb and echoes may be missed at times, dynamics are a bit better than EDA Balanced, overall timbre is accurate and true to life.
• Macrodynamics, how the ESX takes in the larger picture of volume and moves it around and over the whole soundscape of the song? Yeah, no question, it’s amazeballs with that.

Music Analysis

While writing this section, I am listening thoroughly to the tracks that are mentioned, there will be sometimes where I will say coped statements and will be too lazy to explain anything, but yeah, this is the part I enjoy the most so let me indulge just a bit.

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1. Hamu Test “Multiple tracks arranged by Hamu” (Played in HibyMusic)

The tracks in this section, will test the IEM ability to naturally replay and stage musical instruments like piano, guitar, violin and drums. This section will also test imaging, detail retrieval and separation. Most of the tracks here also hates V-shaped IEMs.

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Maaan the tracks in this section are very dynamic, full of energy, organic, 3D-like and wide sounding. All instruments are presented with physicality and very big presence on the soundscape, like at the start of track サクラモチ, it literally sounds like I’m in a sunny sidewalk and there is a musician jamming with his guitar and triangle and some people are walking behind me, I can literally imagine myself at the front of the musician. Instruments are placed in the front, back and sides and the hitting of drums, strumming of guitars and that trumphet..arrrghhh.. so nuanced, heavy and articulated, so good. Additionally, listening to track 流星をくぐって, I can hear how the sound of the waves of the ocean go back and forth at the front and back of my head, while the drums start to jam at the start. Also the bass notes after that….just… starts to pound the soundscape, then decays very cleanly like nothing even happens, like what, what the fudge is even happening, maan..why is the bass flexing like that, its making me love the track even more like whth…. I can’t explain how I love the replay of this song with ESX, I just want to enjoy it damn it!!! Arrrghhh~~

Replay Rating: Beautiful

2. Betelgeuse by Go-qualia (Played in HibyMusic)

Female Vocals, Driver Resolvability, Soundstage, Midrange Nuances, Separation

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Bruh, wth is even happening, this track sounds amazing with EDA Balanced, and ESX turns up the dynamics and fun factor to 11, the overall sound is authoritative and all instruments has this big presence on the soundscape….Maaan.. the bass drop at 01:23 and how Illya voice actor starts to speak, it’s just so well done, the transition and how the bass attacks on the soundscape and how it decays very cleanly, like bruh it sounds soo goood, like what the fudge is ESX even doing with this track. The sense of space is very open, background voices are also articulated in the whole soundscape. However even if the main voice at the foreground is well weighted and tonally correct, it does not have the brightish and clean replay like the EDA Balanced (with EDA you can hear the echo on the voices, yes, all voices, even the background voices.), but maan the presentation of the sound scape is just..just making me ignore the microdetails in the music, and just focus on the fundamentals of the instruments..bruh its just so grand and theatre-like … As Nagi takes the stage at 04:09, she sounds so powerful and her voice is just so luuush…I don’t know what to say anymore, please if you love this track, just..just buy the ESX or even EDA Balanced if you like more details.

Replay Rating: Beautiful

3. All Ed Sheeran Tracks (Played in HibyMusic)

Guitars, Male Vocals, Soundstage, Separation, Staging

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Ahmm. Do I even need to explain the replay of Ed Sheeran tracks with ESX..
To be honest I just want to enjoy his tracks and ignore the little nitbits, I’ll just summarize it with 3 words. hehe
Theaterical, Grand, Lush.

No comment really, if you like Ed Sheeran, ESX is a no brainer.

Replay Rating: Beautiful

4. Machigai Sagashi by Kenshin Yonezu (Played in HibyMusic)

Male Vocals, Midrange Resolvability, Guitars, Separation

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Another majestic track with ESX, just plain beautiful. How the ESX extract the wideness and atmosphere of this song, is just so immersive, mind you this is still the start of the track. As Kenshi takes the stage, the atmosphere retains its wideness, while Kenshi’s lush voice dominate my center space. This track is a bit cleaner with EDA Balanced, however with ESX the instruments are more spread out throughout the soundstage, and there’s a hint of warmth to the overall sound, many will correlate it to being natural sounding. The niche thing here is at 01:01, even with the significant bass drop, the midrange retains its quality and transparency. Plus the contrabass at 02:01, I can imagine them at the furthest right at the back of my head, and I can hear how the strings are being plucked beautifully. If you are an avid Kenshi Yonezu listener you will love the ESX. Cause truth to be told, all of Kenshi tracks are amazingly rendered with ESX, you can feel the weight of notes, the lushness of Kenshi voice, appreciate how Kenshi master his tracks and plays with spatial cues..

Replay Rating: Beautiful

5. Prism from Polyomino Disc 2 by Nagi Yanagi (Played in HibyMusic)

Female Vocals, Midrange Forwardness, Detail Retrieval, Separation, Soundstage

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One of the weaknesses of ESX, to render female vocals with sparkle and render microdetails and echoes on the soundscape. This track is lacking resolution with ESX, the bass is somehow veiling the midrange and instruments feels like one noted. With EDA Balanced this track is clean, transparent and free from any veil or mud, microdetails and reverbs are just retrieved wonderfully and you can feel the atmosphere of the song. With ESX its just not there, it feels like the instruments are fighting for loudness on the soundstage add the enthusiastic bass that doesn’t want to get overtaken. It sounds messy.

Replay Rating: Meh

Frequency Response Analysis


Comparison

This comparative analysis is highly biased on my library, so please don’t take this as a unified guide on what should you buy or not.

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ESX vs CRA+
Think of CRA+ but without the metallic/artificial treble and vocals, and has this wider, deeper, and taller soundstage, that’s how the ESX sounds like. But even with the grander sound of ESX, there will be sometimes where people will still crave for those details in the upper treble that the CRA+ has, in which the ESX trades off with a more organic and immersive signature. For my library, no doubt ESX wins. But if you already have the CRA+ I don’t see any reasons upgrading to ESX, maybe if you like a more open soundstage while retaining the signature of CRA+, then yes upgrade to it.

ESX vs Oppoty (BL-03)
Its like I’m comparing a bicycle here with a motorcycle. ESX is the motorcycle by the way. ESX has better bass control, better soundstage, more accurate imaging, better vocals, even better accessories. I don’t know what BL03 is holding really, timbre? You can get 90% of that with ESX, soft bass that sounds bad with most of my tracks? Yeah nope. ESX wins

ESX vs EDA Balanced
EDA Balanced has better microdetails, sounds more in your face, has better soundstage presentation, has better faster bass response, has better treble extension, has better female vocals rendition, sounds more linear. ESX sounds grander, bigger, authoritative, also has a deeper soundstage, a more analog replay, sounds more dynamic, fun and laid back. I can’t choose helpm…. Tie

ESX vs EDX Ultra
Do I really need to do this? I really despise EDX Ultra upper treble, maybe just for reference, think of EDX Ultra but without the headache inducing upper treble, has better soundstage and is more dynamic and natural sounding, that’s how ESX sounds. ESX wins.

ESX vs Tanya Max (Using Avani)
Yeap, no competition, lol, ESX is just a grander, theatrical and, technical version of Tanya. Like don’t even at me. ESX wins

Mods

ESX sounds bloated and too bassy with stock tips, please and oh please change the tips to widebore (I highly recommend Kbear07 or BGVP W01) if you really want to enjoy them. And please KZ if you are seeing this, your eartips are ruining the sound of your current IEMs.

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1. Kbear KB07
Yes! Recommended (please always include these tips in your KZ purchase cause this IEM makes wonders on their recent IEMs), improves the soundstage and imaging. Also adds more texture to the bass, and make the midrange cleaner, adds dimensionality to the sound and makes the vocals more forward than stock tips.

2. Stock Starline Tips
STAPPPH, No.

3. Radius Deep Mounts
Yeap recommended also, but it cuts the openness of the soundstage of the ESX. Makes the vocals more forward and intimate than Kbear07.

4. KZ Reversed Starlines
Also cuts the bass to a significant degree, makes the midrange and treble pop out more. Adds more width to the soundstage, but reduces the depth and tallness. Vocals may appear may laid back. But still acceptable compared to the stock tips.

5. Spinfits CP145/CP100
Also cuts the bass to a significant degree, makes the midrange pop out more. But also diminishes the depth of the soundstage so yeah. Recommended if you think that ESX is too bassy even with Kbear07.

6. Generic Foam Tips
Almost the same as Kbear07 but less bass texture. Makes the vocals more laid back too than Kbear07.

7. BGVP W01
Kbear07 with lesser bass and wider soundstage, cleaner vocals too.

Equalization
No, it doesn’t need it . Just enjoy its sound.

Tested Synergies
Zenith’s Refined Synergy
(ESX, Kbear07, Abigail)
Smoothest and most dynamic synergy, Abigail will make sure that the bass mud is kept to a minimum while improving the soundstage depth and making sure that the midrange will pop out more. Kbear07 will tighten the bass and provide more room for midrange to shine. Microdetails are also more apparent with this synergy. Also, excellent set for fun, dynamic and fatigue free listening.

It’s All About the Fundamentals
(ESX, Kbear 07, Avani)
You want the super thick instrument fundamentals to slap you with force on the soundscape? Then yes this is a synergy to go for, however microdetails aren’t that audible in this synergy and other may find it too bassy or too heavy. This synergy is more suitable for jamming and losing yourself with the music rather than a critical listen. If you somehow achieved this synergy, try to play some energetic pop songs, and hear what I’m trying to say here.

Recommend Tracks/Genres:
Almost all genres, especially Western/OPM Tracks.

“Not that good” Tracks:
Not really a deal breaker for me, but some Japanese tracks might be too bassy to some. Female vocal centric tracks might also be unsatisfactory.

Shop Links:
https://www.kztws.com/products/kz-esx

Overall Rating
S- (Yes, S-, you reading that right)
Highly Recommended
(Current Top 1 due to the macrodynamics and its overall-theatre like staging, it also has the characteristic of an S-ranker in my list.)
My Ranking Listo!
Asterhythmist

Final Words

Super late to review this..sorry? And also thank you very much for reading my review. hehe
Talking off topic. It seems that there are reported issues with unit variance with some people, I’ve already talked to one of the KZ rep and it seems that it isn’t a batch issue, and just a typical case of Chi-fi unit variance. So take that into consideration if you are considering the ESX.. Also how many times do I need to repeat this…change da tipss ples~~

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This review will be a second tribute on KZ/Knowledge Zenith's 10th year anniversary of its establishment on how they became the game-changer and shifting the paradigm of audio industry. My first KZ product was an IEM with a non-detachable cable and it has a single DD set-up, the model is called KZ ATE. I bought it around late 2016 as I'm really curious about a good sounding earphone with the sound quality of a headphone in a smaller form. After the purchase of ATE, I bought more products from KZ until that I switched to other brands due to lack of progress in tuning. I still value KZ ED16 as one of KZ's best products.




What I have here right now is their decade anniversary product, The KZ ESX. Knowledge Zenith is now refining their single DD line up since the release of KZ EDX as it shows its capabilities in tuning and at least we should appreciate it, to give credit where credit is due on behalf of them.




KZ ESX is a single DD set-up encapsulated in a shell made of hybrid materials such as polycarbonate and aluminium alloy. The transducer of KZ ESX is a 12mm dynamic driver which offer better bass response and better resolution retrieval. This is not the first implementation of 12mm DD as it was previously applied on KZ ZES albeit the ZES was a hybrid driver set up which also includes a magnetostatic driver.




The proportion of shell of this unit is in average size and its faceplate is an aluminium alloy with an aesthetic cue reminds me of an abstract pattern art or a Neo-Picasso, industrial look. Like most KZ's line-up products, it still uses a QDC-type 2 pin connector which I still have some qualms about. As for fitting, it has adequate insertion in my lug holes if I rate it as comfortable enough but the sound isolation is just average as I still hear some noises from outside surroundings.




Packaging of KZ ESX is as usual to all KZ entry-level products, too barebone as included accessories are sparsely basic for its cheaper price offering. It has a small packaging box with illustration of ESX at the front and basic specification infos at the rear.


Its contents inside the box are the ff:

• A pair of KZ ESX IEMs.
• A parallel, flat 4-core stock cable with a L-shape 3.5mm termination plug (with mic version).
• Extra ear tips of different standard sizes (small and large)m
• Instruction manual.
• A KZ 10th year anniversary commemorative token.

The driveable and amplification aspect on this unit is laudable as they scales well to all audio sources even to decent ones like smartphones, tablets and laptops. DAPs that has amplification stages gives even more potential on ESX to improve its dynamics and quality volume output.




When it comes to its tonality, It has that usual V-shape sound signature that we are all familiar with KZ's in-house tuning. Elevated bass and treble with recessed midrange to sound more appealing and relatable to most listeners especially to casual ones.


I'll be describing its sound characteristics from each part of the audio frequency range spectrum based on what I perceived on my observation in this unit.


LOWS/BASS:


This is the eminently part of the ESX and it is its bass quality. It is punchy, robust and thump so that bass heads will be satisfied with its quantity. Sub bass has a good depth reach as I perceive a notable grumble.


Mid bass has a sufficient texture to give a good body on bass instruments. Bass guitars has that growl and weighty sound from each plucking either from slapping to fretless, a good thudding and full pounding on bass kick and a mighty and sonorous sound of bas baritone vocals. Midbass is somehow controlled as it rarely does some smudges that might ruin the midrange part.


In general, KZ manage to deliver a very good bass response on this set that bass heads will truly appreciate this one.




MIDRANGE:


As expected for a typical KZ in-house tuning, Mids are indeed recessed in this one. Despite of that dipped midrange. It is somehow a consistency of its texture to have a sufficient warmth and mellow.


Male vocals certainly benefited on texture as it give an adequate guttural and thicker voice quality. Female vocals are a bit smoothen out and less energetic in my liking on this one as a midcentric, the quality it's tad subdued, soft and compressed. Despite of those qualms that I mentioned, it remains to be melodic and soothing.


As for instruments, strings like guitar and violin don't have the crisp and vibrant sound rather than being muted and austere. The piano's sound is warm and somehow rounded in my liking. Saxs are more warm sounding and sometimes nasally and some brass instruments has that warm dark tuning registry either from bass trumpets to horns. And lastly, snares drums has the dry and less penetrating strikes.


Midcentrics will surely have a diverse impressions on the quality of its midrange especially if they want a more forward vocals and a detailed and precise sound on its instruments.


HIGHS/TREBLE:


This is what I'm bit surprised on how was the treble registry of KZ ESX. I certainly affirm its improvement on treble aspects compare to KZ's previous product offering in single DD segment, it has indeed a smooth, more balanced and less offensive upper mids to presence treble.


Due to smoothen upper mids peaks, it has very minimal amount of sibilance as I still discerningly occasionally hear them more on some sibilant-laden tracks as I still view it as a well-controlled one. KZ even manages to minimize the stridency and harshness cause by some peaks between upper mids to presence. With all these effort to tame down those peaks, there are some caveats which I will explain later.


Cymbals' sound has less shimmer and its sizzle is muted as its extension is fading fast as it has somewhat comparable to a a shorted chick sound of hi-hats which I find unnatural in my perception. The range of treble extension is just average as it has a lack of sparkle and airiness is simply flat and inadequate.



SOUNDSTAGE, IMAGING AND OTHER TECHNICALITIES:


For a KZ product, it is now the widest soundstage among its products. The previously KZ product that I've tested with sufficiently spacious staging was the KZ ED16 and KZ ED16 was a hybrid driver set-up. But if I compare it to other IEMs that I have, KZ ESX has an above average width which I gave it a good mark. As depth and height, that perceived depth is merely average as it isnt that immersive and the sense of ceiling is somehow decently tall. It is has a good proportion and dimensions on all sides of sound field.


Imaging is tad blurry as it does not pinpoint accurately the placements of singers and instruments, separation and layering are more on average as it has enough spacing but it doesn't defined well and a bit muddied on perceived textured on stacking rows of frequency range especially when I play a more complex instrumental tracks.


Due to its newly-developed 12mm dynamic driver. The coherency of its drivers performs excellently. It is fast that it give a better transient and responsiveness to execute a homogeneous sound. Tonal colour is more on a warmer with a tad smoother definition.


As for resolution capability, it's more concentrated on macro details rather than micro details as it has insufficiencies on sharpness, vividness and definition on resolving on such amount of details on harmonics.




PEER COMPARISONS:


KBEAR KS1:

• KZ ESX shell is bit larger and has better design has it has a cubism-inspired aesthetics compare to a more plain and spartan-looking shell housing of KS1.
• Both have similar sound signature, V-shape. Bass is more tactile and impactful on KS1 but ESX has better control on bass bleed and some more balanced, ESX has better mids texture as KS1 is a bit leaner, treble quantity is somehow similar as both of them have average airiness on treble.
• As for technicalities, KZ ESX has better soundstage width than KBear KS1 but terms of imaging, separation and layering, they are very similar.

BLON-03

• KZ ESX is more logical when it comes to an ergonomic shell design than BLON-03's quirk and peculiar one as I still remember my struggles on putting it in my lug holes just to have a good fitting on it.
• Bass is cleaner and more solid on ESX as BLON 03 has that bass bloat that keeps smudging the mids which is very annoying.
• Technicalities wise, KZ ESX edges out the BLON 03 in any category from soundstage to coherency. Wider soumdstage, better separation and driver performance.

KZ EDA (Balanced)

• Bass is more prominent on ESX as it has more thudding and has an impact compared to a more balanced, less haptic EDA.
• Mids are similar, male vocals performance is a bit better on ESX but EDA is more balanced and transparent as it is more versatile on both male and female ones.
• Both treble quality are similar, both exhibit on a smoother and sufficient treble but sibilance is more noticeable on EDA. Technicalities-wise, both are analogous but in soundstage, ESX is wider and feels more spacious than EDA.

As I conclude my assessment on KZ ESX, this unit definitely follows a more familiar KZ in-house tuning, with some improvements of tuning and materials to be more palatable in the even more competitive entry-level of portable audio market. I also expected some sort of change on the packaging of KZ ESX like new included accessories like an improved cable and better eartips since this is their decade anniversary product but it seems that it has the same barebone accessories that we are very familiar with and a decade anniversary token of Knowledge Zenith.


Anyway, KZ ESX is tuned for listeners who are leaning more on musicality and fun tuning rather than being more analytical and "audiophiliac". And in any event, Knowledge Zenith will continue to garner more newer audio enthusiasts who have just started their audiophile journey.


Checkout my other reviews from KZ products for reference and comparisons:

• KZ EDX
• KZ EDC
• KZ EDA
• KZ ZEX
• KZ ZEX PRO
• KZ DQ6S
• KZ ZES

KZ ESX is now available in all known e-commerce sites and currently priced around US$19/ £16.





SPECIFICATION:

MODEL: KZ ESX

IMPEDANCE: 22Ω

SENSITIVITY: 122dB

FREQUENCY RESPONSE: 20Hz – 40KHz

CABLE LENGTH: 1.25M

PIN TYPE: 2-PIN QDC-TYPE CONNECTOR

PLUG TYPE: 3.5mm

DRIVER UNIT(S): (1) DYNAMIC DRIVER


Some Tracks Tested: ( * = 16-bit FLAC, ** = 24-bit FLAC, *'* = MQA, '*' = DSD, *'= .WAV)

Alison Krauss -When You Say Nothing At All *
Jade Wiedlin - Blue Kiss**
Led Zeppelin - When The Levee Breaks **
Mountain - Mississippi Queen *
Queen - Killer Queen **
Guns N' Roses - Patience *'*
Eric Clapton - Tears in Heaven '*'
Sergio Mendes- Never Gonna Let You Go '*'
Pearl Jam - Daughter **
Roselia - Hidamari Rhodonite *
Assassin - Fight (To Stop The Tyranny)*
Celtic Frost- Visual Aggression *
New Order - Blue Monday *
The Corrs- What Can I do (unplugged version) *
Jimi Hendrix Experience - Voodoo Child *
The Madness- Buggy Trousers *
Metallica - Motorbreath **
Mariah Carey- Always Be My Baby *
Destiny's Child - Say My Name *
Malice Mizer- Au Revoir *
Mozart - Lacrimosa *
New York Philharmonic Orchestra - Dvorak- Symphony 9 " From the New World." *
Eva Cassidy - Fields of Gold (Sting cover)*
Michael Jackson - Give In To Me *
Exciter - Violence and Force *
Diana Krall - Stop This World **
Debbie Gibson - Foolish Beat *'*
Lucretia my Reflection – The Sisters of Mercy **
Suzanne Vega – Luka **



P.S.

I am not affiliated to KNOWLEDGE ZENITH(KZ) nor receive monetary incentives and financial gains as they provide me a review unit for an exchange of factual and sincere feedback from yours truly.



Once again, I would like to thank Tyvan Lam for providing this review unit, I truly appreciate on his generosity towards me and other reviewers.

If you are interested for more infos, just click the link below:

https://www.kztws.com/collections/all-products/products/kz-esx

FOREWORD​

• This unit was provided by Knowledge Zenith (KZ) for review purposes
• My ESX has undergone over at least 150 hours of playtime
• I don't do measurements, I just describe what I hear, from my own POV
• I don't use EQ
• The entirety of my impressions was done with my own Foam Tips
• Ultimately, my reviews are purely subjective and biased to my personal preference in sound

EQUIPMENT USED

• CEntrance DACport HD
• Cayin RU6
• Audirect BEAM 3S
• VE MEGATRON + RAP5
• NotByVE Avani
• Xiaomi Mi9T
• HiBy Music Player (USB Exclusive Mode)
• FLAC Lossless Files

The Build


For a 10th anniversary IEM, KZ ESX came in the usual package like most other KZ offerings. Simple boxed set with minimal choices of Silicone tips (of which not one of them usable to my ears). Luckily KZ was kind to send a separate pair of Foam tips which would be a bit more useful for my usage. The stock cable is the newer gen SPC, in my case a unit that comes with inline Mic. About the only thing different from the norm would be the inclusion of a "gold" coin to signify this as a special 10th anniversary unit.

At 22 Ohm and 122db of sensitivity, this single driver ESX is bound to be super efficient and easy to drive, the only other KZ that would probably be as efficient is the CCA CA16Pro.

Now, after spending substantial time with my own ESX, I ended up pairing it with TACables Amber and Misodiko MIX460 tips. I personally find that the stock tips (including the extra Foamies) and stock SPC cables just not working sonically for my preferences. I will just simply say that the stock setup lacked sparkle and resolution.

Sound Impressions​

The entirety of my sound impressions were done with TACables Amber and Misodiko MIX460 Tips.

Click to expand...

Sound Impressions​

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DYNAMICS, TONE & TIMBRE​

KZ ESX definitely is a V curved sounding unit. This is not a surprise at all since KZ has been known to favor this vibrant and fun tuning for the majority of its releases. There's strong emphasis on the lower frequencies with mild elevation of Treble region after Midrange area - of which the Mids itself would appear reined in (as how all V curved devices are).

Timbral balance is organic and warm-ish. It is generally smooth with proper aggression level - not too euphonic, just enough to sound fun and engaging. ESX must be praised for sounding big, I can feel that the overall body of sound is big and expansive. There's no dryness to the Timbre, as per expected of a Dynamic drivers.

MIDS​

Recessed and reined in, the Mids is probably the least appealing feature of ESX. Playing Jazz, Bluegrass and Vocals on ESX will just not work for me. I am hearing the vocals of Diana Krall, Sinne Eeg and Alison Krauss appearing subdued, as if they have taken a few steps back further - almost distant. What does remain admirable, the organic timbre of Mids are present. There's smooth realistic touch to tonality, vocals, note attack and decays for instruments. Piano, violins, percussions Midrange presentation sounding organic and believable - with the caveat that they may appear slightly recessed with forwardness. For non Mids focused music, something like Rock/Indie/Metal, the ESX will then sounded a bit more at home with the general mastering of those recordings. The overall smoothness of ESX Mids can sometimes mask the underlying textures and details.

TREBLE​

ESX Treble is very well controlled to not present itself with unnatural brightness or shimmer. Just like the Mids, it is smooth and well rounded. However I must say that when subjected to high power and aggressive Treble attack, I can hear that the extended region where Treble decays occurs, the trailing end becomes grainy edged with less than graceful dispersal. At times the decays itself would sound somewhat plasticky and non realistic. This is evident when I was sifting through my regular playlist of Black Metal and Instrumental music, which contains lots of cymbals and hi-hats. Otherwise for more relaxed music, the anomalies are less evident. The general theme of ESX Treble being smooth and non offensive. There's ample details and texture to be had within the limit of Treble extension.

BASS​

Perhaps the most prominent feature of ESX, Bass is in abundance. I would even say that ESX is a Basshead IEM for the amount and density offered. ESX Bass reminded me of the other KZ that I liked so much, the HBB DQ6s. Admirably, despite the larger than neutral Bass responses, it is disciplined enough to not bloat all over the place. It has enough speed to not sound sluggish. Mid-Bass offers commanding rumble, kick and punch, with Sub-Bass boasting vibrant seismic sense - absolutely fitting for Electronic and Dance music. I was having some serious fun listening to Controlled Bleeding, KRAFTWERK, Depeche Mode etc. with ESX. Worth to mention that both Mid-Bass and Sub-Bass remained respectful of each other spaces, thus preventing the tendency to muck things up in a mess. I must also commend for the amount of smooth texture of Bass in general.

TECHNICALITIES​

ESX offers big open sound, the soundstage is admirably wide and spacious, lots of air. Spatial positioning being holographic and immersive. However I would describe the overall resolution and imaging being a little fuzzy. Body definition seemingly lacking sharpness - perhaps as a result of over-smoothing. There's details here and there, but again the overall smoothed out resolution may hinder some micro details presentation.
Speed wise, ESX is quite respectable. It does not crumble when subjected to outright speed and complexities. Despite the less than surgical separation lines, I can still track individual notes which remained stable even when the passages gets really busy.

SCALABILITY & SYNERGY​

Being super efficient, ESX is best served to pair with equally lower powered sources. 1 Vrms dongles is more than enough. Subjecting it to 2-4 Vrms dongles may exhibit some tendencies for ESX to become grainy edged as noted with my impressions on the Treble segment.



Final Thoughts
Frankly, I expected more of this ESX. Perhaps the 10th anniversary moniker have asserted higher expectations on my end. Among the many KZ IEMs I have ever used, I will openly say that KZ HBB DQ6s and modded KZ ZEX (Non Pro) remain the ones that I like the most. KZ ESX does not bring anything new to what is a known KZ house sound (of which DQ6s does it better). Perhaps the best appeal of ESX is that, this is a special anniversary IEM that will serve great as a collectible unit. I can only rate an IEM based on what I am hearing, and I find it hard to rate this ESX higher - but this can be purely subjective to my taste and preferences. Nonetheless, I hope that KZ will continue to make great budget oriented IEMs and the learning curve for them will only gets better with time.

Disclaimer:

• KZ sent this unit to me in an exchange for an honest, unbiased review. Rest assured that this review will try its best to deviate from any bias/es.
• The following remarks and observations shall be made and owned only by me.
• No monetary compensation is/was involved before, during, and after the period of creation of this review.
• Your mileage may (and always, will) vary.

Burn-in time: 5-10 hours per day, 5 days.


Source/s used:

• Hidizs AP80
• VE MEGATRON USB DAC
• Zishan U1 USB DAC (AKM Variant)
• Cyberdrive Feather DAC
• Non-HiFi smartphone (realme 5i, Samsung Galaxy On7)
• Local Files via Foobar and Roon, YouTube Music, Deezer, and Qobuz with UAPP.

IEM/Earbud/Setup configuration: Stock white medium eartips, KBEAR 07 eartips, stock cable, any form of EQ or MSEB off, 40-60% volume, both high and low gain, with and without extra amplification.

Sound signature:

• U-shaped sound signature that leans to the bassier and warmer side of the spectrum. On smartphones, it will sound v-shaped. Basically this shares the same sound as what the KZ EDA Balanced have, with added bass quantity and quality while keeping the EDA’s excellent technical performance among all KZ IEMs.

Lows:

• The lows are elevated here in the KZ ESX. Despite being elevated, this is tight, impactful, and punchy. Subbass is a bit elevated here over the midbass and it reaches deeper levels when the track needs it. Decay leans to the faster side of the spectrum while keeping the texture decently. Bassheads on a budget might want to check this as this delivers that engaging bass for their EDM and bass heavy tracks.

Mids:

• The mids here are slightly recessed but has the same levels of presence as what the EDA has. It never got drowned or sounded muffled during my observations. Lower notes has decent thickness and depth to it. Upper mids are elevated with a very good amount of clarity, air, and presence. Higher than usual volumes may make the upper mids “hot” but far from being harsh or sibilant. Overall, the ESX retained the EDA’s presentation and quality of the mids - it’s just that the mids of the ESX is not at thick but it is as smooth as the EDA. But still, their differences in terms of quality isn’t that too far - both still sound very good for a budget or even an IEM under 40USD.

Highs:

• The treble on the KZ ESX is elevated but not as elevated compared to the lows. The treble is well-extended here and is airy with no instances of harshness or piercing observed. Cymbal crashes and splashes here are crispy and well-presented. Detail retrieval is above average and can present microdetails very easy. This is one of those IEMs that can pick up small nuances in Joji’s Ballads 1 album with ease.

Soundstage, Imaging, and separation:

• The soundstage of the KZ ESX is wide. It somewhat retains the soundstage of the EDX Ultra with the KZ EDA’s layering quality. It is wide with above average levels of expansion depending on the track played. It is still wider than deep with a very good amount of height. Separation here is what I would call “excellent” for this price point since it did not struggle too much on very busy tracks compared to its sibling IEMs like the KZ EDX and EDX Pro, ZEX and the ZEX Pro, and the DQ6s. It will manage very busy tracks decently. Imaging here is also precise as I can here the vocal and instrument presentations clearly with a sense of spaces between them, particularly on live performances.

Pros:

• One of their “best” KZs so far.
• Non-harsh, crisp sound.
• All rounder, u-shaped sound signature.
• Has the KZ EDA Balanced technical performance.
• Elevated, controlled bass.
• Open-sounding mids
• Airy treble
• Excellent detail retrieval for a KZ IEM.
• Easy to be driven properly.
• Design is a quite beautiful (subjective)
• One of the best IEMs under 20USD in my book as of today.

Cons:

• On higher than usual volumes, upper mids may get a bit “hot” but far from being sibilant.
• Nozzles are a bit longer than usual and may wobble on most ears.
• Stock eartips degrade the IEM’s sound quality.
• Packaging and accessories aren’t that “special” for this IEM, given that this is a 10th anniversary edition IEM.
• A cable winder would be a treat for everybody (my nitpick).

Pairing recommendation/s:

• Source: The KZ ESX is very easy to be driven fully with a smartphone. However, USB DAC will help to bring the mids a bit forward.
• Eartips: The stock eartips did not fit me well and it degrades the sound. I recommend using KB Ear 07 Eartips or a wider bore eartips.

Thank you for reading!
Product link! (Non-affiliated): https://shopee.ph/KZ-ESX-Special-Ed...anceling-HIFI-headset-i.345922933.15485591735

Additional Photos:

My thanks to KZ for this sample, as always nothing influences my opinion but the music.
Specs.
Headphone type: 12mm LCP Dynamic drivers
Pin Type: 0.75mm
Cable Length: 120±5cm
Plug Type: 3.5mm
Frequency: 20-40000Hz
Impedance: 22Ω
Sensitivity: 111.59±3dB

The package is similar in size to the typical KZ but much more extensive graphics, this is an anniversary edition as they been making IEM for ten years. Inside is the ESX, tips in three different sizes, a decent cable and a commemorative coin. The build is great resin on back and a pretty design on the metal faceplate. The isolation was above average and improved with a tip change. They are comfortable even in bed they worked well.

Sound:

Bass is very controlled with a good presence in the Sub-Bass it's got good texture, speed and details. Mid-Bass is punchy and does bleed a little into the MIds.

Mids are clear with a rich natural presentation, there is a little recession as with most V-shapes and lower Mids have a pleasant warmth. They are forward and both female and male vocals sound natural and full.

Treble: Is airy and controlled well enough there are some peaks, but it rarely gets harsh. treble has good details and sparkle but smooth in its presentation.

Soundstage: Is wide as it is deep having excellent separation and layering. The imaging has accurate placement, and I would recommend this one for gaming.

Conclusion: KZ has done a great job with this one, while it has some quirks it is by far an improvement over others I've used. I think with some mods this could be a favorite.