Disclaimer and intro
Zach Mehrbach, the founder and designer of ZMF has kindly lent me this Caldera Closed in exchange of my honest opinion.
Last year I
reviewed the Caldera open and compared them to my Meze Elite. After spending months with both headphones, I fell in love with the Caldera open's rich, organic texture and dynamic, lively sound: I had to order my own pair.
Fast forward to May 2024, the closed version of the Caldera has just been released. I was really intrigued to hear and discover the differences. The question arose: would I like the closed version even more?
Burnt Ash (Shou Sugi Ban), one of the current stock woods.
Closed-back headphones in general and thoughts on other ZMF models
I will be upfront; in general, I really dislike closed-back headphones. I see them as a necessary compromise, in case someone does not have access to the 'full package' of open-back headphones and needs isolation. My experience is when we close the back of the headphones, we lose a serious amount of airiness, space and naturalness. Furthermore, designers face an awful lot of challenges to direct airflow, reverb and cup reflections versus the natural airflow open cups offer by nature. This often results in odd sounding headphones: claustrophobic soundstage, poor instrument separation, boxy treble, hollow midrange, over-damped or too bright sound. Even headphones like the Denon D9200, Audeze, HiFiMan, Focal or Sennheiser closed-backs are not free form some of these problems.
I admit, I am more sensitive to their shortcomings and more critical with closed-back headphones than the average consumer: for me closed-back headphones have always been the 'necessary bad'.
Zach has developed a unique and original, patented airflow and damping system.
Here you can read about it in more details, but to sum-up the result: ZMF closed-back headphones sound the most natural to me out of all closed-backs I have heard. When listening to ZMF closed-backs, I do not feel I have to make terrible compromises or that, there is something really off with the sound. ZMF is the only brand whose closed-backs I am actually able to enjoy. That said, I still prefer the open counterparts of all ZMF models, but the difference between them is not as enormous as it is with other brands.
As many of you already know, Zach started out with Fostex T50RP modifications, which are planar headphones. Then he went on a different journey and developed several models with dynamic drivers. Since the very beginnings, he had a 'super planar' in mind which manifested in the Caldera open in late 2022. This is a completely in-house design from scratch, even the transducers are designed and developed, built by ZMF. (They have patent pending on their magnet structure.)
While I tried all ZMF models at different auditions and shows, the first pair I bought was the Caldera open.
Dynamic driver ZMF headphones almost have a cult-like following, and I am saying this the kindest possible way. Many people religiously love the synergy of high impedance ZMF dynamic headphones and OTL tube amps and I can clearly see why. There is some organic, thick, warm, lifelike and musical, engaging, euphonic magic going on between tubes and dynamic ZMF headphones.
I come from the planar world, mostly owned Audeze, Final and Meze headphones before the Caldera. To me personally the Caldera open is the best ZMF. They are special in the sense that the advantages of dynamic headphones and planar transducers somehow meet in one chassis. The Calderas (both of them) have a natural, organic tonality and thickness, richness that is often associated with dynamic drivers, yet they have the technical edge of planar transducers: enhanced speed, extension, clarity, detail retrieval, resolution. To my ears the Calderas offer the best of both worlds.
Some say, the Caldera deviates the most from the original ZMF house sound. I tend to agree, if under deviation we mean improved clarity, relative neutrality and higher level of technicalities. Still, the organic ZMF signature sound is absolutely there, and that is why I fell in love with my Caldera open.
User-tuneable headphones
ZMF is also famous for its highly user-tuneable headphones. You can tune the sound to your liking with several ear-pad options and damping meshes. It is not uncommon to have 8-12 different tuning options with certain models. These meshes and ear-pads can truly change the sound, so experimenting is highly recommended if you feel the headphones are good, just
'not quite there'. I am almost certain, that with some patience you will be able to find your
'yes, that is it!' combination.
The Caldera closed comes with a thick mesh and hybrid pads as stock. The tuning kit I have here includes another, thinner felt mesh and three more ear-pads; full leather (protein), full suede and thick leather.
Caldera closed with the thinner black felt and Caldera open without any mesh or felt. They both have carbon fibre rings.
On my open Caldera I tried five different ear-pads and settled down with the thick leather pads with no mesh. These pads tame the upper-mid/lower-treble forwardness just enough for long-term listening and slightly emphasise bass, plus smooth out treble a bit. Thick pads on the Caldera open are ever so slightly warmer to the more neutral stock option, but to my ears it is a welcome adjustment to the energetic and dynamic, yet most organic sounding king of planars.
I will come back to the tuning options of the Caldera closed a little later.
A few words on comfort, weight and build
ZMF headphones are a feast for the ears and for the eyes. The individually crafted wooden cups are simply gorgeous; like a musical instrument made for order. Weight can vary a lot depending on the wood type, but Calderas tend to hover between 470g-600g. To my surprise, there is no difference between the weight of open and closed Calderas. I would have thought the full wood cups of the closed version weigh more, but the stock Ash closed Caldera I have is 510g which is significantly lighter than my open-back black&white ebony Caldera with its 560g. Open-back Calderas can go down to 470g with redwood cups and magnesium chassis, and on the other end of the spectrum you have the stabilised and hard-wood versions around 600g.
The weight alone should not scare away any customers, as weight distribution and comfort are top notch. There are plenty of options to add more padding to the headband and buy the lighter magnesium chassis. My open Caldera has the 'BBB strap' which is the simplest and most subtle headband upgrade: a wider leather strap under the headband improving weight distribution. The demo Caldera closed does not have the BBB strap, it came with the basic stock headband. I have to say, thanks to this $59 addition, my 50g heavier open Caldera feels significantly more comfortable than the stock closed pair. After a while I feel the weight of the closed Caldera more, than I do with my own open Calderas. Clamping force is also stronger on the closed version, I am not sure if this is to balance the effects of the simpler headband or these headphones are just less worn in.
My point is, I would highly recommend the BBB straps to anyone who considers a purchase. My previous daily drivers before the Caldera were the Meze Elites, which are true comfort kings. Even after the Elites (430g) I have no weight or comfort issues at all with my 560g ebony Calderas.
I cannot miss mentioning the unique shape of the ear-cups. These asymmetrical dips and dives are not only aesthetic design elements, but they also serve a sonic purpose inside the cups and contribute to achieving a relatively lighter physical weight.
I applause, when a manufacturer dares to be different, and for me this unique design is an absolute hit; I love it. I read different opinions from people who cannot get their head around not having the same round cups like on any other headphones, but hey, more talk means more marketing.
Where is the Caldera positioned on the market from a sonic perspective
Since I have a Caldera open as my daily driver, I am clearly biased, but will try to bring in some objective insights. These observations are true for both the open and closed models, I will go into the differences between them a little later.
I owned many nice headphones and extensively auditioned flagships I did not own.
I usually gravitate towards planar headphones, as I really enjoy their speed, clarity, linear bass that effortlessly extends down to 20Hz and so on. At the same time, I prefer a thicker, slightly warmer, more euphonic and natural sound as opposed to neutral and analytical perfection. For these reasons I picked Audeze, Final and Meze planars as opposed to the thinner and more diffuse sounding but arguably more 'technical' offerings from HiFiMan for example.
In my opinion the Caldera is the most organic and natural sounding planar with the best timbre, texture and bass slam I have heard so far. They are not as detailed as a well-driven Susvara can be, but they are not far off and sound meatier. The soundstage is not as big as it is on the Meze Elite, but the ZMF flagships separate even better. Bass can be pretty much equally good as it is on the Abyss 1266, but with ZMF's more organic flavour and more alive midrange. The Final D8000 series are also wonderful headphones, but for me the Caldera once again has better dynamic range and a uniquely appealing, organic aliveness.
Caldera closed versus Caldera open sound
After discussing open versus closed design in general and where I think the Calderas stand on today's market, let's look into comparing these two models directly.
At my very first listen of the Caldera closed I was more surprised about the differences than struck by the similarities. Of course, the same Caldera sound is preserved in the closed cups, but to me these headphones feel more like cousins and not siblings. As mentioned earlier, I do not feel the serious compromises with ZMF closed-backs that I feel with other closed-back headphones; the sound is still natural, not congested or limited in any sense. Yet, in direct comparison the end of the soundstage bubble on the closed Caldera is palpable, while the open model sounds, well, more open and airier without the sense of a finite background. When listening to the closed version only, this space limitation is not bothering at all, yet in direct comparison to the Caldera open, becomes apparent.
Another thing that was instantly obvious is the warmer and softer tuning of the closed version versus the more neutral/slightly brighter and more dynamic sounding open-back wooden beauty. There is no better or worse here, just different which I think will divide the audience more or less equally.
Natural imperfections often enhance beauty.
Zach said, he tunes the closed-back versions of his headphones a little warmer on purpose: closed-backs tend to sound brighter and sharper, therefore more damping needs to be applied. This results in a warmer (and apparently softer) sound versus the open versions. There are many people, who absolutely love this warmer and softer approach: after all most ZMF headphones are tuned like this to smaller or larger extent. For example, fans of the Atrium, who found the Caldera open too bright and energetic, will most likely welcome the more familiar tuning of the Caldera closed with its softer treble and warmer overall tone.
On the other side of the coin, those who love the Caldera open for its supreme dynamics, detail retrieval, energy and impact might find it slightly disappointing that the closed Caldera will not offer the familiar, punchy fun to the same extent. Do not get me wrong, the Caldera closed still retains the fabulous tonality of the well-known ZMF Caldera sound, but inevitably it is wrapped into some damping material which will round off those dynamic edges and tame the overall energy of the open version.
To me, as someone who generally dislikes closed headphones, this is still an acceptable compromise which says a lot about Zach's patented air flow/damping system. I could live with the Caldera closed, but to me it is still a 'B variant' of the original which I would only use if I needed isolation.
The sound is wonderful, just not as open, not as airy as the first iteration. With this necessary damping we also seem to lose a few percentages of details and clarity compared to the open version: not much, but a noticeable amount.
This is a common theme throughout the frequency spectrum, so I won't go into too many details regarding bass, mids and treble. The closed version of the Caldera is smoother, warmer, slightly darker, less dynamic and a little less detailed than its open counterpart. Bass is still fabulous, just not as snappy and punchy. In stock form you get more mid-bass quantity, but clarity, precision, speed and impact are superior on the open version. Vocals are more forward on the open Caldera, a little further away in the closed model. Mids in general are more pronounced on the open, and slightly more recessed on the closed pair. This gives a modest sense of V-shape curve versus the opens. I would not call the Caldera closed V-shaped in general, but in direct comparison to some extent they appear to be.
Those, who found the Caldera open treble too bright or too energetic, will love the softer and easier treble tuning of the closed version. Those, who love the open version, might miss the bite, dynamics and energy that they are used to.
I personally miss the outstanding dynamics, clarity, slightly better technicalities and liveliness of my open Caldera. This is why I was trying to tune the closed-back version closer to my open pair, using the available ear-pads and meshes.
Earpads and meshes
As of now, the Caldera closed comes with the thick mesh installed and the hybrid pads on. I think, the hybrid pads are a good choice for stock pads, as they are the most balanced out of the four. The hybrids have relatively good bass focus, but also sound airy and natural in the upper-mids/treble. The leather (protein) pads improve bass focus, speed up transients, give more energy to the attack. In other words, you get a more focused and punchier bass, but at the small price of a slightly less open upper frequency range.
The suede pads are great choice for mid-centric music, vocals are the nicest and most natural on these pads. Bass and treble however become too soft and loose to my liking, lacking dynamics to make EDM enjoyable.
Hybrids are the 'in-between' solutions, but I personally love the attack and punchiness of the protein pads, so I am willing to make the compromise of a slightly less airy treble.
With the thick pads I liked the bass and treble response, but for me they suck out mids too much. Vocals are not just more distant, but also become a little bit hollow to my liking.
I personally found the stock felt mesh a little too much as front damping. To me these make the sound slightly too thick and warm. I prefer the thinner mesh, as they add a bit of brightness to the treble.
Not using a mesh at all just makes the sound too bright, falling out of balance: a mesh is necessary, but for me the thinner one is enough.
With the thin mesh and leather pads I was able to bring out the best slam, most focused bass and quickest attack from the Caldera closed. This is the closest I was able get to the open Caldera's dynamics.
The open version still sounds more natural, airier, quicker, more detailed and more energetic, but with the above-described tuning combination I felt I am not losing out too much on dynamics.
Other enthusiasts will love the increased warmth and smoothness of the closed Caldera with stock thick mesh and different ear-pads. Diversity makes the world a beautiful place and the huge variety of ZMF tuning options really widen the potential audience of these wonderful headphones.
Gear used
EverSolo DMP-A6 (streamer only), Holo Cyan 2 R2R DAC, Flux Mentor, Schiit Mjolnir 3, Cayin HA-3A (Bendix 6V6, E80CC).
Out of these
three wonderful amplifiers I personally prefer the Cayin. The Mjolnir 3 brings out the most outstanding bass slam, but it lacks resolution and refinement in the upper frequencies compared to the other two amplifiers. The Mentor is refined and highly detailed, but for my personal taste lacks the life that tubes breath into vocals and acoustic instruments. The Calderas are happy on both solid state and transformer coupled tube amps; you just have to pick the correct tubes for a smashing bass experience. (OTL tube amps need to be avoided with low impedance planars.)
Finishing thoughts
The Caldera closed did not change my perception of closed versus open headphones. Still, I think currently these headphones are amongst the best three closed backs on Earth. Which are the other two? In my opinion they are the Verité closed, and Atrium closed. The ranking between these three will be completely subjective. For me personally, the Caldera closed are the best closed-back headphones I have heard to date.
If I needed sound isolation, ZMF would be my go-to brand, but luckily, I am able to use open headphones all the time; therefore, I will stick with my beautiful open Calderas for now. My choice does not change the fact that Zach has just put down yet another masterpiece on the lavish table of the world's audiophiles.