"Smooth like Butter": Ryan Soo Reviews the Apos Caspian

Note: This article is based on the article "Apos Caspian Review – Smooth like Butter" written by Ryan Soo on his website and is printed here in partnership with Ryan Soo. The review was originally posted on September 28th, 2022. It was also published on The Headphone List on October 3rd, 2022. Edits have been made for clarity and length. You can purchase the Apos Caspian on Apos Audio

Pros –

Solid construction, Appealing design, Class-leading bass slam and tightness, Non-fatiguing and natural voicing, Very easy to drive

Cons –

Recessed vocals, Treble extension leaves to be desired, Pads could be deeper, No balanced cable, Headband could be wider

Verdict –

This headphone never once feigns balance but delivers excellent bass performance from a snappy driver that allows it to achieve surprising genre flexibility

Introduction –

Apos Audio is best known as a retailer renowned for their frequent sales and after-sale support. However, the company surprised many with the release of their own products in the form of the Flow headphone cables that were perhaps testing the waters for something much bigger. Such has finally been realized in the form of the Caspian, a fully-fledged Apos-original headphone designed and built in conjunction with highly-esteemed Kennerton and tuned by experienced reviewer Sandu Vitalie of Soundnews fame. The Caspian enjoyed a lengthy design process and is a clear passion project for all parties involved. It is of personal belief that the $500 price range is fairly sparse of all-rounder headphones albeit representing one of the most diverse range of offerings that isn’t seen either above nor below this price range. The Caspian joins the movement as a headphone that was designed to be coloured and stylized to the creator’s liking; something easy to drive with a timeless styling, forgiving and personable.

The Caspian just launched for $499 USD. You can read all about it and treat yourself to a unit on Apos Audio!

Disclaimer –

I would like to thank John from Apos very much for his quick communication and for reaching out to organise a review of the Caspian. All words are my own and there is no monetary incentive for a positive review. Despite receiving the headphones free of cost, I will attempt to be as objective as possible in my evaluation.

Contents –

  • Page 1: Intro, Unboxing, Design
  • Page 2: Sound Breakdown
  • Page 3: Comparisons & Verdict

Specifications –

  • Driver: 50mm Graphene-Coated Multi-layer Dynamic Driver
  • Frequency response: 5 Hz – 45 kHz
  • Impedance: 33 Ohms
  • Sensitivity: 115 dB
  • Weight: 378g

Behind the Design –


Apos delves much deeper into the design process on their blog here. Apos eludes to the fact that the Caspian is a close relative of the Kennerton Vali in terms of design but mention little of the similarities between their respective 50mm drivers. They are of Kennerton origin and sport an extremely low-mass multi-layer composite diaphragm in addition to being mechanically de-coupled from the housing. The company claims this provides a more responsive, lower distortion sound. In addition, the diaphragm is fortified by a graphene layer that improves rigidity and with it, speed and decay. It was then custom-tuned for Sandu and Apos.

Easy to Drive

A large goal of the Caspian was to make a coloured headphone that would be easy to enjoy for the average audiophile in addition to being non-demanding on other parts of their setup. This means the headphone must be easy to drive and Apos posit that its high 115dB sensitivity mean it can even be enjoyed from the integrated audio solutions in phones and laptops.


The Caspian isn’t a cheap headphone but justifies its asking price with a premium BOM – Apos has a post all about the process here. This starts with handmade oak earcups sources from the Caucasus mountains that has excellent acoustic properties and a crack-resistant grain. The company spent additional effort balancing the two earcups for each headphone both acoustically and visually, and this shows in the final product. The earpads have an inch of acoustic memory foam and are wrapped in hand-stitched sheepskin leather. The headband shares a natural leather construction atop a tough stainless-steel frame.

Unboxing –

The Caspian comes in a large box that flaunts Apos branding alongside model designation. Opening up the box reveals a small but quality set of accessories. The star of the show is undoubtedly the leather carrying case which offers protection during shipping but also excellent portability with the addition of a shoulder strap and hand hold. It has a lovely uninterrupted grain and a supple feel. There is plenty of space for the headphones which means the pads don’t get compressed nor do the sliders have to be retracted before storage, something that irks on many competitors. In addition, Apos includes a standard fabric-sheathed cable with a single-ended termination and an in-built albeit non-removable leather fastener.

Design –

The Caspian lacks the complex mechanisms and flourishes of some in favour of simple, solid fundamentals. Their streamlined styling gives them a timeless appeal, aided by lovely oak cups that are beautifully complemented by a matte black frame. This lends an almost murdered-out aesthetic that perfectly pairs with their darker sound tuning. I admire the effort put into matching the two sides with woodgrain running in similar directions and a distinct lack of imperfections or fillers. While I am not a huge fan of lacquered wood personally as I do prefer the texture of unfinished wood, finished woods do tend to wear better over time which was a goal of the design. They also don’t feel over-finished as some cheaper wooden headphones do. The alloy grills similarly inspire with nigh flawless machining and a tactile texture. The tolerances overall are very tight reinforcing the sense of quality despite its simplistic design relative to many competitors.

Speaking of which there are really no unique design features to note besides a good old-fashioned padded headband, slider and single-axis earcup adjustment. This headphone is surely a reminder that more isn’t better as they never left me wanting in terms of fit or feel. Mini-XLR connectors leave at an angle from both earcups, and the connectors feel tight and reliable. The included cable is a 6.3mm single-ended unit with a fabric sheath and uniform chromed connectors. I appreciate the rubber strain relief on the mini-XLR connectors and the cable is surprisingly supple and free of memory despite its thickness. Microphonic noise also isn’t an issue despite the tight fabric sheath as the cable above the Y-split is quite short, preventing rubbing. Still, given the Apos make their own balanced Flow cables, the inclusion of one for the asking price may have been justified.

Fit & Comfort –

Over the years I’ve tested a plethora of headphones some from experienced companies and many from aspiring ones. Of those, you do get a sense that it is extraordinarily difficult to produce a headphone that both feels solid during handling but also conforms comfortably to the head during wear. While it doesn’t balance these qualities to the extent of Meze’s pricier designs, for instance, the Caspian manages both with better success than many likely owing to the experience carried by the staff at Kennerton. This starts with the headband assembly that Apos boasts is derived from Beyerdynamic’s OEM. It’s a traditional padded design which was a little thin for my liking but more comfortable than most. I did notice the headphones would wear on the top of my head after several hours of listening but it wasn’t unbearable. The frame otherwise impresses with its solidity and smooth finish devoid of sharp edges. The joints and slider mechanism all offer even tension throughout the adjustment range and between the two sides, further enhancing the sense of quality on offer. That said, there is only a single axis of earcup adjustment, up and down, with no pivot.

This means they don’t perfectly conform to the head but this impression will vary based on individual head shape. In my case, I found that fitting the headphones so that my ears were as far back in the pads as possible produced the best comfort. This was especially so as the driver waveguide is slightly convex leaving a little more room on the edges than the centre – take note if you’re experiencing hotspots.  On the flipside, the lack of wobble lends the headphone an even more solid feel. What leaves to be desired is the slider mechanism whose distinct lack of feedback makes reliable adjustment a little more difficult than most. In addition, the hanger hinges and slider covers are both plastic with a rubberized coating that will not wear as well as the remainder of the headphone. Even after just a few weeks, the coating was already pealing from one of the hangers.

I am more enamoured with the hand-stitched sheepskin earpads that offer a supple feel and an inviting scent. While they aren’t quite as soft as the lambskin used on many high-end headphones, they do appear more hard-wearing. In addition, the padding offers a great seal with thick, high-density memory foam stuffing. The dense nature means that, even when softened due to body heat, the foam never becomes overly compressed. This prevents the drivers from contacting the ears over longer listening sessions. I do think they could do with a little more width, as my average-sized ears were just barely accommodated. However, as above, I didn’t experience hotspot formation over time from the pads themselves.

Sound –

Tonality –

I was expecting a reasonably warm and laid-back sound given the sound descriptors at play in addition to the initial graphs showcased in Apos’ blog posts. This is pretty much what has been delivered, a warm, bass-centric sound with mids and highs sitting in near equal proportion above. Vocals sound clear albeit laid-back whilst the top-end is crisp with some lower-treble sustain that tapers off into relative darkness above. I have found that headphones around this price range tend to excel in one particular area with more rounded performance coming in at a higher price or to the detriment of technical ability. This resonates on the Caspian with regards to its bass performance which is outstanding within this price range and a generally fun and engaging performer. If you enjoy a bassy sound that doesn’t neglect the remaining frequency ranges but retains them in a clean and non-fatiguing manner, the Caspian strikes me as a strong performer with a very focused and clear-cut character. It’s certainly not a groundbreaking style of tuning but one of thoughtful execution and with pleasing driver qualities to complement.

Bass –

The highlight of the sound in terms of both quantity and quality, the low-end sits at the forefront of the Caspian’s sound but doesn’t overwhelm it. It’s a very progressive boost meaning the timbre comes across as quite honest despite sitting forward. There’s a medium deep-bass boost giving bass a bolder character, however, the mid and upper-bass showcase sound linearity resulting in minimal bloat and bloom. This produces a powerful sounding low-end with good structure and surprising separation given the level of emphasis. While I don’t want to paint the Caspian as a bass-head headphone, it is definitely bass-forward, especially evident on tracks with male vocals that tend to be quite laid-back.

Thankfully, the driver quality is an inspiring performer, especially considering their asking price. Extension is excellent, delivering a more palpable slam than competing planar models that gives the low-end a sense of dynamism and physicality. In addition, note definition performs at a high level and notes decay naturally contributing to the natural note timbre on display. While bass isn’t what I would consider pacey, it offers a very tight impact and never drones or smooths over fine details. Notes are highly textured and presented with a larger-than-life character imbuing a sense of scale and grandness. With minimal bloat or smear, the low-end is characterized by a fun, dynamic yet discerning nature. 

Mids –

If there’s one thing that is neglected in this price range, it would be the midrange and, unfortunately, the Caspian doesn’t go too far against the grain here. Many competitors simply suffer from wonkiness in their frequency response but the Caspian’s main issue is its vocal-recessed nature. The actual voicing is mostly natural through its lower and centre-midrange but with a sizeable dip in the 3kHz region, vocals have a notably dense and laid-back character. Some may enjoy the organic and coherent voicing this permits, and both clarity and vocal size remain ample on behalf of a small 4kHz rise. In addition, the headphones pick up somewhat in the lower-treble region retaining a good sense of articulation and extension. This is a headphone that has intentionally been tuned this way, but it is important to note that it still won’t be to many listeners’ preference. The headphones don’t strike me as veiled, especially after a brief adjustment period, but they won’t win any awards on vocal clarity either.

This is most evident on male vocals that are quite recessed with female vocals sounding slightly more transparent and present due to the upper-mid rise if still not especially immediate. The lack of bass to midrange contrast also gives the midrange a very full-bodied character meaning vocal definition is lacking. Still, I do keep coming back to the sense of grandness I enjoyed in the bass. The same character is maintained in the midrange which benefits from a rich and full-bodied portrayal of instruments. Though vocals rarely take the spotlight and just suffice in terms of quality and timbre, the midrange instrument portrayal is subjectively more enjoyable. The Caspian is ultimately a clearly coloured affair and does make some concession in midrange voicing in favour of a more vibrant bass performance. While the midrange doesn’t inspire, it has an easygoing quality that also lacks the glaring faults that plague many competing bass-centric headphones.

Highs –

Typical to many bass-boosted headphones, treble has a small rise to help balance out the overall sound profile. However, I would say it is in very good taste here, neither sounding blunted or closed-off nor overbearing by comparison to the laid-back midrange. It sits roughly on par with the upper midrange and sustains linearly throughout the lower treble before rolling off progressively thereafter. The even nature of the treble response means the headphone has a good sense of foreground detail presentation in addition to the driver offering above-average resolving power. The leading edge of notes is crisp and not the slightest bit over-sharpened. Foreground treble instruments such as strings and cymbals benefit from a well-textured and clear expression. At the same time, they never overstep or fatigue due to their slightly laid-back positioning. If there’s one notable quirk of this headphone’s treble response it would be the middle treble. As emphasis falls off around 8kHz, air and openness are reduced.

Notes strike with accurate clarity and notes are well-bodied. However, the subsequent decay is truncated leading to an overly damped sounding treble. It does sap some liveliness and shimmer from the sound though as the lower treble upholds good clarity, I didn’t find this to hamper listening enjoyment. Just don’t expect an especially airy, open sound here. In addition, background and micro-detail retrieval are just average performers, not aided by recession through the responsible frequency ranges, and these qualities are easily bested by most similarly priced planar models. Unsurprisingly, this style of tuning rewards in the form of a dark, clean background with zero glare and fatigue over time. You can enjoy these headphones all day and even turn up the volume a little higher without issue. All the while, they maintain a clear and well-detailed lower-treble presentation.

Soundstage –

The Caspian isn’t an especially spacious sounding headphone but provides sound expansion that prevents its warm and dense voicing from becoming claustrophobic or congested. Width is just enough, it never stands out as a strength but isn’t lacking either though you will find no shortage of open-back headphones that will best the Caspian in this regard. Where the Caspian does well is with regards to depth, achieved with its grand sound tuning combined with its laid-back yet well-centred vocals. Imaging performs at a decent level lacking both outstanding speed and balance. Layering is average but the stage is well organized and offers good stereo positioning. Separation leaves a similar impression and isn’t helped by the style of tuning. With that said, it is a respectable performance considering due to the well-controlled driver.

Drivability –

The Caspian was designed to be easy to drive with a high 115dB sensitivity and a low 33 Ohm impedance.

Output Impedance

Testing the Caspian with and without a 20-Ohm adaptor produced a similar tonality suggesting that the Caspian has a flat impedance curve. This means it can be enjoyed from tube amplifiers or other high output impedance sources without huge tonal deviation.

Driving Power

The Caspian, true to its design, is not a difficult headphone to drive in terms of volume or current demands. Even portable sources do a fine job and deliver a similar tonality with minimal loss to bass power. There is a tighter slam on a good desktop amplifier in addition to a more physical sub-bass slam, however, besides this I found there was impressive parity.

Suggested Pair Ups

To me, the warm, smooth Caspian is best paired with a neutral-leaning amplifier that aids transparency. The THX789 was a fine choice in my testing, adding a bit of definition to the treble and further tightening up the bass, it also makes sense from a budgetary standpoint. If you lack the budget for a dedicated source, a strong advantage of the Caspian is that is is easily driven by integrated audio solutions, dongles and portable players which still isn’t completely common in the headphone scene.

Comparisons –

Hifiman Sundara ($299): The Sundara is a very well-rounded offering that isn’t a giant killer by any means but is surprisingly versatile especially considering its increasingly lowering cost. The Caspian has it beat in terms of build quality with a better cable and more solid frame, it also has slightly deeper albeit small pads for those with wide ears. Sonically, the Sundara is immediately the more balanced option making it more genre versatile. The Caspian is more bass focused and this is its main advantage over the Sundara. The Sundara has a light warm mid-bass and good definition, but the Caspian blows it out of the water in terms of extension, dynamics and tightness. The low-end is far better developed on the Caspian in addition to being more forward. The Sundara is cleaner and more balanced, boasting better separation but also lacking the same impact.

The midrange isn’t perfectly balanced on the Sundara but is a pleasing performer. It has a more balanced presence with just slightly warm and laid-back vocals. Both are naturally voiced, but the Caspian is further recessed and full-bodied albeit, not to the extent of veil even in direct comparison. The Sundara has a more prominent top-end giving it a u-shaped character. It has more mid-treble meaning its notes are thinner but also clearer and airier. The Caspian doesn’t have quite the same extension and background detail retrieval but a more linear lower treble with a more accurate timbre. It is more laid-back but similarly detailed in this area. The soundstage is wider on the Sundara but deeper on the Caspian. I perceive the imaging as being superior on the Sundara as is separation.

Sendy Audio Apollo ($499): The Apollo, like many other competing offerings at this price, offers a planar driver. It also shares a wooden design. The Apollo is a dark, almost v-shaped headphone. It has less bass focus than the Caspian but a similar sense of recession in the midrange. The bass is fast and mid-bass focused to some degree but also lacks in the dynamics department. This contrasts to the Caspian which offers awesome sub-bass extension and kick alongside a thicker note structure in general. While the Apollo has better separation, the Caspian sounds similarly defined. The midrange is much thinner on the Apollo giving it a clearer expression.

The Caspian is warmer yet but has a more natural voicing with more accurate vocal size and a bit more presence. The Apollo is less consistent track to track due to its roomier nature and wonkier midrange tuning in general. The treble is where the Apollo makes more of a case for itself. The Apollo is quite evenly tuned as well but has superior extension giving it a more vibrant, spacious feel. The Caspian is darker, cleaner but also more closed in. The Apollo also has a slightly cleaner transient response with a noticeable bump in fine detail retrieval. It also has a slightly wider stage though the Caspian has better imaging and depth.

Ovidius TX-901 ($499): The Ovidius is a newcomer to the market, offering a planar driver and metal build for a similar cost. Despite being heavier and almost entirely metal, it has some wobbles and loose joints that give it a cheaper feel. On the flipside, I do feel its deeper pads and suspension headband offer slightly better long-term comfort. The Ovidius is more balanced through the bass and treble but has odd, recessed vocals that mire its performance. The low-end is stronger and bolder on the Caspian. It extends deeper offering thicker, more weighted notes and a more concise slam. The TX-901 is cleaner and more linear with better separation. Despite this, both have similar separation. The TX-901 decays a bit quicker but lacks the same texture and dynamism. The midrange is more tonally neutral on the Ovidius but it has a very odd vocal dip that gives it a strange voicing.

It sounds overly roomy and its vocals sound off. The Caspian has a more natural voicing but also a more coloured one with greater warmth and body. It has less separation and is also a bit more recessed than the Ovidius albeit without the odd voicing. The top-end on both sees some lower-treble bump but differs in the mid-treble where the TX-901 sees a second peak, the Caspian a dip. The Caspian is more linear in the lower treble, its notes are more natural and accurately bodied with greater texture. The Ovidius has a slightly more defined leading edge, retrieving more fine detail at the cost of a thinner note. The Ovidius has greater air but doesn’t have much of an extension or sparkle advantage. The Caspian has the more organized stage to me and it has superior depth and imaging.

Audeze LCD-X 2021 ($1199/1699): A substantially more expensive headphone, the revised LCD-X shares a similar style of sound. This means buyers that desire this style of sound may consider saving up for a more versatile option. The LCD-X is a bigger, heavier headphone but that also affords it much larger pads and a wider headband. It is a much more balanced headphone overall. The Caspian has quite a bit more bass, especially deep bass. This gives it a much bolder note presentation. By comparison, the LCD-X sounds far more linear, it doesn’t have quite the same slam but is tighter, faster and more defined by a good measure. This compounds with its more balanced tuning. The Caspian has better dynamics and a thicker, more textured mid-bass that some may prefer. The midrange is more present on the LCD-X too and it shares a natural voicing.

It’s on the dense and coherent side but isn’t at all lacking clarity or openness. The Caspian is much more recessed here and it sounds much warmer and stuffier. The LCD-X has much better separation and definition alongside a far more transparent tone. However, these two represent foils in this regard making it more a matter of preference. The two are more similar in the treble with even lower trebles and some mid-treble darkness. The LCD-X differs with a far better extended and sparklier upper treble that gives it a more micro-detailed and energetic sound without adversely affecting body and timbre. The Caspian sounds darker and cleaner yet but lacks the same layering and resolving power. The LCD-X has a larger stage, especially width and much sharper imaging. It represents a more balanced take on a dark, low-fatigue sound that makes it a far more versatile choice if also a far more expensive one.  

Verdict –

The Caspian strikes as a bass/dynamics specialist within its price range with a low-end that performs at a level exceeding essentially all similarly priced offerings. However, ironically it is its mature execution elsewhere that really sets it apart. Bass indeed stands out in terms of both performance and presence but this is not to the detriment of its natural midrange and treble. The build quality inspires as does the fit for the most part, and it has an attractive design appropriate for the price point. Being easy to drive is the cherry on top, meaning you can enjoy its standout dynamics and a consistent sound signature from the vast majority of sources. I do also feel that, as enthusiasts or reviewers, we tend to lose touch with the wants and preferences of average listeners. In this sense, though the Caspian is far from an ideally balanced sound, it is one I can see being quite popular with non-audiophiles and enthusiasts wanting this specific style of tuning. This headphone never once feigns balance but delivers excellent bass performance from a snappy driver that allows it to achieve surprising genre flexibility.

The Caspian is available from Apos Audio (International) for $499 USD at the time of writing. I am not affiliated with Ovidius or Linsoul and receive no earnings from purchases made through these links.

Track List – 

Billie Eilish – dont smile at me

Bob Seger – Night Moves

Courtney Barnett – Rae Street

Cream – Wheels of Fire

Dire Straits – Communique

Dirty Loops – Next To You

Eagles – Hotel California

Elton John – Honky Chateau

Fleetwood Mac – Rumours

H.E.R – I Used To Know Her

Jasen – BYE

John Mayer – Continuum

Kanye West – Ye

Missy Higgins – The Sound of White

Radiohead – OK Computer

TALA – ain’t leavin` without you

The Beatles – Abbey Road

The weeknd – After Hours

Vampire Weekend – Father of the Bride