Testing Methodology: Measured using Arta via IEC 711 coupler to Startech external sound card. 7-9KHz peaks may be artefacts/emphasised due to my measurement setup, less so with deep fit. Measurements besides channel balance are volume matched at 1KHz. Fit depth normalised to my best abilities to reduce coupler resonance. Still, due to these factors, my measurements may not accurately reflect the earphone or measurements taken by others.
The Zen 4 is surely one of the less conventional earphones I’ve tested and this is apparent looking at the FR graph alone. However, it still achieves a pleasant balance and a sound profile that will appeal to a good range of listeners. At face value, the Zen 4 is a roughly L-shaped monitor with a warm bass, dense, laid-back vocal range and organic top-end with uptick of crispness in the lower-treble. It’s a mellow but articulate sound that, nonetheless, avoids too much tonal colouration in the midrange. That is not to say the timbre is perfect, vocals are distinctly full and dense in exchange for openness, definition and clarity. This forms a pleasantly coherent sound if not the most linear or transparent one.
Whether due to the ADEL module or not, the Zen 4 sounds a lot more typical than its FR might suggest. There’s a good sub-bass extension for a BA monitor, not the highest pressure due to those ADEL modules, but a tight, concise slam that’s well above average. The mid-bass and upper-bass, especially, are both moderately forward which provides a full, warm if somewhat tubby bass note. However, this also imbues a pleasant richness and punchiness into the presentation. As there is a 2kHz trough, there’s good separation of the vocal range from the bass, thereby avoiding veil and excessive chestiness.
Bass quality is greatly aided by the Zen 4’s agile note presentation, as one would expect from a good BA setup. Attack is concise and decay is on the quicker side too, helping to retain separation despite the fullness of the low-end. Notes are not the highest definition as a result of the tuning but bass is hardly muddy or poorly detailed. There’s a smoother note texture due to these factors but overall, a tight, tactful note expression with good separation. The Zen 4 isn’t a bassy earphone to reiterate nor is it the most engaging. What it provides is a well-metered quantity and euphonic warmth and fullness with pleasing if not outstanding depth and detail retrieval.
The midrange tuning is a little unorthodox, especially in lieu of the upper-bass forward low-end and moderate lower-midrange bolstering. The 2kHz dip especially, is quite uncharacteristic in earphone tuning. Yet it does help to redeem some bass/midrange separation at the cost of a more laid-back vocal presentation, giving instruments precedence by comparison. Still, vocal clarity and size are retained by 3kHz hump that places vocals just behind the bass presence wise. There’s a subsequent dip at 4kHz for density, compounding upon the Zen 4’s warm and full-bodied voicing with increased density that solidifies a highly coherent midrange expression. Of course, the overall presentation isn’t especially accurate or linear by comparison to a lot of competitors but that is not to say that it doesn’t work in and of itself. The Zen 4 is without a hint of rasp, thinness or plastic timbre, being instead organic and impressively natural in its voicing.
They remain clearly coloured with additional warmth and smoothness. Nonetheless, much like the bass, the presentation isn’t veiled or overly smoothed over and there remains ample clarity and note definition if not representing an outstanding performance in this regard. Surprisingly, the top-end of this monitor is quite articulate; and this was confirmed to me when listening to a sine sweep that revealed an uptick of 6-7kHz presence relative to the midrange. Of note, this wasn’t apparent on the FR graph even after repeat measurements so perhaps it is due to ear canal resonances or the ADEL module – I lack the knowledge to talk in absolutes here. Regardless, this does help to lift the openness and clarity of the presentation. There also isn’t a chance for thinness or sibilance to creep in due to the otherwise full-bodied and dense nature of its voicing. Altogether, the Zen 4 is a little laid-back and quite warm in tone, albeit coherent, smooth and refined with ample texture and top-end clarity working much to the benefit of definition.
As aforementioned, the top-end is defined by its pronounced 6-7kHz region with a very dark and clean background by comparison. This instigates a crisp presentation with good detail presence and retrieval, sitting in-line with the midrange and by extension, just behind the bass to my ears. Treble attack is a touch on the smoother side imbuing a slightly warmer tone into treble instrumentation. It definitely lacks the hard-edged attack that some BA monitors have, however, the Zen offers strong fine detail retrieval as its foreground pops in context of its dark and well-contrasted background. Resultantly, the Zen 4 provides similar levels of detail presence and retrieval without the same sharpness and fatigue.
Instrument body is slightly thin as the presentation is not the most linear here, albeit I am not hearing isolated peaks but a general elevation of the lower-treble that is neither strained nor metallic. Above, the earphones offer a dark, clean background on behalf of a noticeably less present middle and upper-treble. Accordingly, decay is a little truncated so instruments such as cymbals, though possessing good clarity, miss some texture and sparkle is barely present. In return, the Zen 4 offers excellent contrast with a focused delivery of foreground details and a clean background that offers enough resolution to enhance the perception of distance and dimension.
The Zen 4 offers a well-rounded soundstage that expands just beyond the head. Imaging is a highlight, the Zen 4 offering very accurate localization with concise directional cues and a generally balanced albeit, not the most linear signature. It offers good layering with its enhanced foreground/background contrast, the clean background especially making small details and cues pop a little more than most. Due to its fuller voicing, the Zen 4 offers a very coherent presentation with plump, wholly resolved notes albeit with enough attack and balance to uphold a good level of separation. The midrange likely suffers most in this regard, being both full and dense, vocals can struggle for air on certain tracks. Still, the appeal of the Zen 4 lies in its very stable and grounded presentation that offers great multi-dimensionality.
The Zen 4 offers a standard 28-ohm impedance and a high 113 dB sensitivity. I found it required a little more power than most in-ears of similar sensitivity due to the slightly higher impedance. However, in turn, they didn’t pick up as much background noise.
To analyse the effect of output impedance, I connected the Zen 4 to an inline switcher connected to the THX789 (1-ohm) and Hiby R6 (10-ohms). Despite their higher impedance, I noticed a pronounced difference between the two sources. The THX 789 provided noticeably more bass extension and presence. In turn, its midrange was larger and more forward, the higher output impedance producing a distinctly brighter and more treble focused sound. As such, a low output impedance is imperative, even if you prefer a cleaner sound, it is at the loss of too much bass extension.
The Zen 4 requires quite a bit of volume, more than a lot of BA in-ears despite its high sensitivity. On my THX 789, I usually hover around 20% of the volume dial but found myself turning it up closer to 40% for the Zen 4. However, despite requiring more volume than most, the Zen 4 isn’t otherwise difficult to drive. It sounded pretty similar to the desktop stack on the Cozoy Takt-C. Of course, the quality of the source will also come through such as the wider soundstage on the THX amplifier.
Suggested Pair Ups
As seen above, the Zen 4 works best with a low-impedance source and one with a slightly higher power output. This is since noise will creep in if you’re maxing out the volume of your source so keeping some headroom always helps to deliver a cleaner signal. In turn, the Zen 4 doesn’t pick up noise too easily. In terms of sound, the Zen 4 is quite flexible. As its warmth stems mostly from the upper-bass rather than mid-bass, I found that warmer sources like the Shanling M2X were still quite a good match. Similarly, the top-end is quite dark so brighter sources don’t introduce any glare. I personally prefer a cleaner source since it helps to retain separation as the Zen 4 can sound a bit too full otherwise.
Campfire Audio Polaris II ($499): The Polaris II offers a much bassier and more aggressive V-shaped sound. Its bass is substantially more prominent, especially in the sub and mid-bass. It digs deeper with its dynamic driver and provides greater slam and rumble in turn. Its notes are a lot fuller and warmer, also distinctly tubbier in timbre. The Zen 4 offers a more quickly decaying and balanced presentation here with higher definition while the Polaris II is more engaging and textured. The midrange is a bit more laid-back on the Polaris II, despite its much larger bass and treble, it has a more forward upper and centre midrange.
The Zen 4 sounds more natural and coherent, the Polaris II being a bit warmer in its voicing albeit not too much fuller due to a large lower-midrange dip. The Polaris II has a bit more top-end clarity. The Polaris II has a more aggressive lower-treble. It has thinner instrumentation but a bit more crunch and texture than the smoother Zen 4. Meanwhile, the Zen 4 offers a bit more fine detail retrieval. The Polaris II has a larger soundstage in both width and depth while the Zen 4 has more accurate localization and imaging.
Oriveti OH500 ($499): The OH500 offers a more W-shaped sound with slightly better overall balance. The OH500 has better sub-bass extension and more sub-bass presence, delivering a bolder bass note. However, it is much cleaner in the mid and upper-bass, sounding more tonally neutral. The Zen 4 is quicker but also fuller so both come across with similar definition, a hair more on the Zen. The midrange is more forward on the OH500, mitigated by a smoother articulation. The OH500 also has a more accurate vocal body and a more neutral midrange tone, the Zen 4 being warmer and fuller.
The OH500 has better clarity due to its greater upper-midrange extension while the Zen 4 is denser and smoother with more laid-back vocals. Both are smoother overall, the OH500 just being more on the defined and revealing side, the Zen4 on the laid-back and organic end. Both have similar levels of detail presence, the OH500 being a touch brighter. The Zen 4 offers slightly more lower-treble detail retrieval while the OH500 has a bit more resolution and headroom at the very top. The Zen 4 has a larger soundstage while the OH500 has much better separation.
Fiio FA9 ($599) Stock Switch Settings: The FA9 is a similarly tuned earphone but more balanced. It has slightly better bass extension with more sub-bass slam. Both are warm and similar in quantity, the Zen 4 being a touch bassier. The Zen 4 has better sub-bass definition while the FA9 is a bit cleaner in the upper-bass having more defined notes higher up. The FA9 also has a slightly laid-back and smooth and full in their expression. However, the FA9’s bass being a little cleaner offers a slightly higher definition in the midrange.
Meanwhile, the voicing of the Zen 4 is a little more natural than the FA9. It has slightly more accurate vocal size too. The FA9 has a hair more openness at the top. It has a crisper lower-treble with a warmer tone, the Zen 4 has sligthly sharper attack and greater fine detail retrieval here. Meanwhile, the FA9 offers stronger extension and noticeably greater headroom. It has a larger soundstage, especially width and sharper imaging. Meanwhile, the Zen 4 offers a slightly better portrayal of distance, making it slightly more multi-dimensional.
Custom Art Fibae 2 (475 EUR): The Fibae 2 offers a cleaner and generally more traditional tuning. Its bass is not as extended but is similarly warmer leaning. The Zen 4 has slightly more bass quantity overall in addition to greater sub-bass presence, delivering more defined rumble and a more solid slam. The Fibae 2 has slightly better definition and speed. The Fibae 2 also has a more accurate midrange, its vocal positioning is just a touch forward and the tone is cleaner. It remains lightly warm but is mostly accurate in vocal body, generally well-balanced.
The Fibae 2 is just a hint over-articulated, the Zen 4 is a bit more laid-back but also richer and smoother in its presentation. The Fibae 2 offers a crisper lower-treble with sharper attack. The Zen 4 meanwhile is noticeably smoother in its expression with a cleaner transient response that makes it a little more detailed to my ears. The Zen 4 has slightly better top-end extension and greater resolution, in turn. Both offer similar soundstage expansion, the Zen 4 being a touch more spacious. The Fibae 2 has sharper directional cues while the Zen 4 has a slight edge on localization and layering.
Craft Ears Craft Four (550 EUR): The Craft Four is a more W-shaped monitor. It offers better bass extension and similar bass presence overall, but is a bit cleaner in the upper-bass. It also has some mid-bass emphasis, but comes across as a bit more balanced and defined. The Zen 4 offers a more organic voicing but sounds a bit woollier in turn. The midrange on the Craft Four sits in better balance with its bass, the Zen 4 having a more laid-back vocal range. The Craft Four has more accurate vocal body and tone. It is lightly warm but also offers better vocal extension through the upper-midrange.
Both have a smoother articulation; the Zen 4 is fuller and smoother yet which makes it a bit more coherent and rich sounding. The Craft Four sounds more transparent while retaining some musicality. The Craft Four has a crisper treble with a sharper transient response. Both sound very clean, the Zen 4 is a bit more laid-back here, the Craft once again more balanced. The Craft Four offers noticeably better fine detail retrieval while the Zen 4 is smoother and a tad more organised on busy tracks. The Zen 4 has a larger soundstage all around while the Craft Four has sharper imaging.
The Zen 4 is a ghostly earphone, its super slim design and lack of wearing pressure enabling it to disappear in the ear. Similarly, the sound is dark, smooth and unassuming with quick focused transients set to a jet black background. Bass also impresses with its extension and kick while the midrange upholds a natural voicing yet with a presence region that pops with its strong focused presentation of details. The timbre is not perfect, being distinctly warm and full, in turn, not the most revealing, open or defined. Those wanting the most balanced, accurate and high-definition sound surely will want to investigate other options. However, if you’re looking for an earphone with class-leading comfort and a sound that won’t fatigue for hours on end, the Zen 4 is a good contender.
The Zen 4 is available from Inearz (International) for $599 USD at the time of writing. I am not affiliated with Inearz and receive no earnings from purchases through this link.
Track List –
Bob Segar – Night Moves
brb. – relationshit
Crush – Digital Lover
Gorillaz – Plastic Beach
Kansas – Audio-Visions
Mac DeMarco – 2
MAMAMOO – reality in BLACK
MGMT – Congratulations
Radiohead – Pablo Honey
Rich Brian – 1999
Seal – Seal
Spoon – Ga Ga Ga Ga Ga
Stephen Speaks – No More Doubt
TAEYON – Purpose