ZMF Caldera Closed - Pinnacle of Closed-Back Performance

4.5⭐️

 

+ Dynamic and revealing tuning reminiscent of the Caldera Open with a slight bass boost

+ Planar bass is quick with impressive resolution and texture

+ Clean midrange with natural timbre

+ Sparkly and airy treble without sibilance 

+ Top tier technical performance

+ Impeccable build quality and materials

+ Optional tuning kit and pads provide variability and customization

- Stock red mesh overdampens the tuning

- Tuning kit is an extra cost and an absolute necessity for me

- Could use a healthy bass boost

- Soundstage not super impressive (somewhat expected due to closed-back nature)

- Size may be too heavy and cumbersome for some

- Yoke rods can be difficult to adjust

- Needs power

- Expensive 

thaslaya's star rating system:

☆☆☆☆☆ - Fantastic!

☆☆☆☆ - Recommended

☆☆☆ - There are buyers but not for me

☆☆ - Can't see the appeal

☆ - Product is a failure

Disclaimer: 

This pair of headphones was provided for a demo period through the Watercooler Headphone Edition tour. I receive no compensation, and all thoughts and opinions are my own. A big thanks to ZMF for supplying the goods and @goldwerger for coordinating the tours!

I also feel the need to add another disclaimer here. I am a completely portable listener and have no desktop gear to speak of. That means I only utilized dongle DAC amps to power these full-sized headphones, which may be sacrilegious to some audiophiles. If that's a dealbreaker, then feel free to read no further.

Non-affiliate link for those interested:

https://shop.zmfheadphones.com/products/caldera-closed

Gear used: 

● Samsung Galaxy S25 Ultra

● HiBy R3 II

● Various DAC amps

Source:

● Listening was done using Amazon Music HD/Ultra HD and local FLAC files. 

Introduction:

Zach Mehrback is the founder and creative mind behind ZMF Headphones. This homegrown company operates out of Berwyn, Illinois, right here in the US. Zach's passion is on clear display in every set that the company produces. Each headphone is handcrafted, and thanks to their ever-growing list of international dealers, they can be enjoyed around the world. I have had the privilege of reviewing a few models in the past, including the Bokeh Open, Atrium Closed, and the Caldera Open. I really like the original Caldera, but I do favor closed-back for the better isolation, so I jumped at the opportunity to try this version. Like its open-back counterpart, the Caldera Closed (CC) utilizes planar magnetic drivers with ZMF's own CAMS technology and comes with a price tag of $3500. Let's break down this TOTL closed-back model from ZMF and see what it can do.

Build, fit, ergonomics: 

I can't speak to the unboxing experience since this tour unit didn't include the retail packaging, but thankfully it did come with some of the stock accessories and even the optional tuning kit. The Caldera Closed shares much of the same superb build quality as the open variant. The leather bull bolster band (BBB) strap is thick and sturdy, while the headband assembly is soft and supple with nice padding underneath. The metal chassis is very sturdy, but the yoke rods can be a nuisance to adjust. One thing I noticed is that the wooden cups have a more unique shape this time around. According to ZMF's marketing material, "the Caldera Closed for the first time uses a geometrically 'Caldera Volcano' influenced cup shape, with asymmetrical dips and dives that allow the sonic character of our driver to shine through. A unique shape that feels amazing in the hand and much lighter on the head than you could ever imagine." Now I'm not sure that I can agree with the claim about being lighter on the head, as these feel heavier and bulkier than other models I've tried, and the size of the cups is noticeably bigger too. I feel like they stick out further from the head and look a bit odd, so while the uniquely shaped cups may help the sound, they definitely contribute to feeling big and cumbersome. The Caldera Closed comes in two choices of wood: shou sugi ban ash and zebrawood. The tour model is made of ash and it has a lighter color with a very unique style and pattern. The chassis is also available in either aluminum or magnesium (for an extra $250) and it comes stock with a choice of either hybrid or suede pads. There's also an optional tuning kit available for an additional $160 that includes a total of four sets of pads and three tuning meshes, which I'll talk about later. Like all ZMF headphones, the CC utilizes mini 4-pin XLR connectors on the cups. Unfortunately, the cable that accompanied this tour unit is terminated in 6.5mm, which I don't have a use for, so I used an aftermarket FAAEAL 4.4mm cable instead. The unit did come with ZMF's Pelican-style carrying case, which offers great protection and durability. Overall, I have come to expect immaculate build quality from ZMF, and I was definitely not disappointed this time around. I'm also always appreciative of the potential for customization thanks to the filter and pad options.

Sound impressions:

Before I get into the sound, I want to clarify that all of my impressions were made using the black mesh filter and the thick leather pads. I will talk more about the differences in filters and pads further down in this section. The overall tuning of the CC is not too different from its open-back counterpart. I would describe it as having a nearly neutral or slightly W-shaped tuning with a small sub-bass boost, light emphasis on the upper midrange, and a well-extended and airy treble. As far as drivability goes, this one definitely needs power to perform its best, so don't think any little dongle will be able to power these well enough. The note weight is about average, yet thankfully I don't find it to be as thin as the open-back version. The detail retrieval is absolutely fantastic but not to the point of over saturation, and the CC has a musical undertone below that superb level of detail. I do find that the soundstage is not really expansive, and it's a little disappointing. While the stage has ample width and height, the depth feels lacking. It does rival many of the better IEMs I've tested, but I expected more from ZMF after reviewing the Atrium Closed last year, which has a very impressive stage, even for a closed-back set. As expected, the timbre is natural and one of the best parts of the technicalities. The dynamics are also quite impressive, and the tuning holds up exceptionally well at any volume level. The imaging is also strong, but it might not be a real standout feature at this price point. The separation is fantastic, and the Caldera never struggles with complex tracks. This, in combination with the great layering, makes for a well-separated yet still absolutely cohesive experience. Overall, I find that the Caldera Closed shares many of the fantastic technical qualities as the open-back version, though it's not quite as focused on extreme precision. The soundstage is not as expansive as I hoped for, though the slight shift towards a more musical presentation is most welcome.

Since the Caldera requires a decent amount of power, I reached for the iFi Gryphon, which thankfully was more than up to the task. Unfortunately, I found the Gryphon's DAC to be less than an ideal pairing, as it makes the Caldera a little thinner, brighter, and more clinical-sounding. Thankfully, though, the Gryphon can be utilized as a standalone amplifier, which allowed me to pair it with the various other DACs I have available. I didn't find the Caldera Closed to be super source sensitive, but there are a few pairings that stuck out to me. The FiiO RR11 seems a silly device to use here, but it did inject a bit of an analog flavor into the sound, though the loss of detail was noticeable. Still, some may find that it takes just enough of the edge off the energy level without sacrificing too much. The two pairings that I found to be best for me were the HiBy R3 II and Questyle M18i, and both imparted a bit of a different sonic flavor. The R3 II adds a touch of warmth and musicality, which helps to take the edge off the treble energy. The M18i, on the other hand, maintains the note weight and overall clarity without affecting the balance or tonality one way or the other.

Here, I'll add some brief observations on the differences between the various types of pads. From my understanding, the CC comes stock with the medium-thickness leather option. In my experience, there's not a ton of difference between the stock pads and the thinner leather pads, but since the thickness of the pads determines how close or far away the drivers are to my ears, the treble energy changes slightly. The suede pads do lend a bit more openness and airiness to the CC, but they also lose just a notch of bass quantity, which I don't prefer. My favorite pads by far are the thick lambskin leather. Moving the drivers a bit further away not only improved the balance between bass and treble for me, but they also make more room for my larger-sized ears, which adds an extra layer of comfort.

Now let's talk about tuning filters, which in my experience makes a much more drastic difference than pad rolling. For me, finding the right filter made a huge difference and can't be understated. Upon my first listen of the Caldera Closed, I was a bit dumbfounded. I thought, "how could they take the energetic clarity that is the Caldera Open and turn it into this just by closing the cups?" As it turns out, the installed filter on this demo kit was the stock red one, which left me quite underwhelmed. It simply made the CC sound too boring and bleak by attenuating much of the crisp and clear nature of the treble. Female vocals lacked that forward fierceness that I fell in love with in the open-back version. Sure, there's not a hint of sibilance with the red filter, but I think it simply neutered the tuning too much. I almost wrote off the CC right then and there, but I'm glad I persevered and tried the thinner black filter next. What a difference it made! It was like turning on the bathroom light first thing in the morning after stumbling in half asleep, brain still fogged and full of drowsiness. But just as the eyes take a minute to adjust to the light, my ears and brain acclimated to the difference this filter made. The treble came back with a vengeance, yet not quite in the same capacity as the open-back Caldera, which is exactly what I had hoped for. I found the energy, clarity, and engagement that had been missing when using the red filter. That certain specialness that makes the Caldera Open both a wonder and simultaneously too intense, like Icarus flying too close to the sun, had been abated to the point of tolerance without losing its luster. It's safe to say that I highly prefer the black tuning filter, but there are still two more options to discuss. The green filter is even brighter than the black and it allows more air and treble energy to emerge. This one gets closer to the sound of the Open, but it's also fatiguing for me. Lastly for true treble enthusiasts (or masochists), the option to remove the filters entirely is always there. As a treble sensitive person, this configuration is by far the worst, but I'm sure some out there may prefer the unfiltered, energetic clarity that the Caldera's planar driver is capable of.

●Lows - As far as quantity goes, I'd say the bass is just slightly above neutral. It's a bit more sub-bass oriented to my ear but still has a decent balance between sub- and mid-bass. I would welcome more mid-bass though to add a touch of warmth. The bass is also really well done from the perspective of overall frequency balance, but I wouldn't go as far as to say it's particularly "fun." The good news is that the low end has top-notch performance and many of the qualities I associate with planar drivers. By this I mean it has a very nice speed, a clean texture, impressive resolution, and a decay that is on the quicker side but still manages to sound natural. All in all, it reminds me a lot of the Caldera Open but with a slight boost; however, if I'm being honest, I was hoping for much more quantity in the CC. Utilizing the XBass+ on the Gryphon gives me the bigger boost I was hoping for, but I really think having more bass in the stock tuning would elevate it to an entirely new level of awesome and help set it apart from its open-back counterpart. Overall, the bass performance is unquestionably fantastic, but the quantity is a little disappointing and leaves me wishing for more.

●Mids - Here in the midrange, it's a slightly different story. Vocals are positioned just a bit forward and sound very clear. They also exhibit nearly the perfect combination of cleanliness, smoothness, and emotive qualities I look for. There is also a really great balance between upper and lower mids too, and both male and female artists are represented equally. While the upper midrange is definitely emphasized, it never becomes shouty or harsh, and the lower mids have a nice weight without sounding veiled or boring. As I said before, the Caldera has amazing timbre, and that is on full display here in the midrange. Vocals are of course well suited to this particular driver, but I think the real magic is in how the Caldera portrays instruments. Orchestral arrangements are exceptional, and if I could procure this set only for that one specific genre, it would not be a wasted effort. Overall, the midrange of the CC impresses just as much, if not more, than the open-back version, depending on personal preferences, of course. This model trades just a bit of the intense midrange clarity for a touch more musicality and emotion that I simply can't get enough of.

●Highs - Let me put any worries to rest; the treble of the Caldera's planar driver is still fantastically energetic, even in a closed-back configuration. The difference here, though, is in the choice of which filter mesh you choose. Like I said above, I found the black mesh to be the Goldilocks choice for me since the red tends to dull the treble too much and the green makes it a bit too sharp and intense. The extension and air are just as good as I remember on the Open, but now with a better overall balance thanks to the slight bass boost and refocused midrange. The crisp and snappy texture remains intact, which still impresses. Cymbals and hi-hats have the distinct punctuated crispness I have come to expect without being overly splashy. Snares too pop with a healthy energy, yet are never too piercing or wince-inducing. Maybe the most noticeable thing about the CC's treble is the slightly toned-down nature of brightness in favor of a bit more musicality and smoothness. Don't get me wrong, the treble is still sharp and concise, yet sibilance is easily held at bay, and harshness is a rarity even at high volumes. The Caldera's treble has always been a huge part of its magic for me, but here in the closed-back version, I find the overall frequency response to be better balanced, and the filter also makes a huge difference in abating just enough energy while preserving the planar driver's special qualities.

Comparison:

Unfortunately, I didn't have any other full-sized headphones on hand for comparison, but I can at least add a few remarks about two of the other ZMF models I've reviewed previously based on my aural memory and some recent CanJam demo sessions (so please take this with a huge grain of salt). To my ears, the CC definitely addresses some of the issues I had with the open-back version. There's a little more bass this time around, and the treble is less bright and zingy, all while preserving the natural timbre that I love. The technical performance is maybe a touch below the Caldera Open, notably in the soundstage, separation, and detail retrieval, though this is somewhat expected due to the nature of open-back versus closed-back headphones. The Atrium Closed is another ZMF set that I was very impressed by, and it was my favorite closed-back headphone until the CC usurped that title. The CC has less bass, of course, but also a better sense of refinement and engagement that the Atrium can't quite match. It also has noticeably better detail and separation, which only adds to the CC's overwhelmingly strong sense of clarity. The Atrium Closed, though, is a bit more laid-back and easygoing, thanks to the more reserved treble response. I will say I was a bit surprised to find that the CC has a better-balanced midrange, and the way it represents male vocals in particular is great. The Atrium Closed, though, still has the absolute best soundstage of any closed-back set I've come across, and could definitely be considered the more fun set of the two. 

In conclusion:

I was so incredibly excited to finally get the chance to listen to the Caldera Closed. I had really been looking forward to this one since reviewing the open-back version last year. While the Caldera Open was a bit too hot in the treble for me personally, it has such a clean and crisp sound signature and the amazing technicalities demand attention. It also has a level of energy and excitement that may be fatiguing over time but also helps make it engaging and effervescent. In contrast, the Caldera Closed adds a little more bass presence which I appreciate and a much more tolerable treble. With the stock red filter, I found it to be much easier to listen for long periods but it's ultimately missing that sense of specialness I came to expect from the planar driver. Well thank ZMF for swappable filters because it's not an understatement when I say that the black filter option absolutely saved this headphone for me. When using the more mid-centric and warmer tuning of the red filter I just didn't find myself connecting to the music the way I usually do with that particular sound signature, though in fairness I'm more used to hearing it in IEMs. I believe thats because the CC relies on the treble to draw out the special unique qualities it needs to showcase the insane technicalities of the driver. The black filter helps to bring these qualities back to the forefront while simultaneously staving off sibilance and fatigue. Unfortunately my experience with the CC isn't all butterflies and rainbows. The other thing I was hoping for besides a more tolerable treble was a much bolder bass response. While it's true the bass quantity is slightly elevated and the low end hits a little harder this time around, it's not nearly enough for me. Now, I don't require earth-shattering levels of bass, but I would love a few more decibels to get my toe tapping and head nodding more. As luck would have it, though, the iFi Gryphon comes with XBass+. Pushing that little button brought an immediate smile to my face but also made me acutely aware that this is the level of bass the CC deserved from the start. Still, I can't really fault ZMF since the CC was never touted as a bassy version of the Open, but I think they missed a golden opportunity to create something truly special. Another minor nitpick I have is that the soundstage width is a little disappointing. Now, before I get crucified for this criticism, I have to say that the Atrium Closed manages to have a stellar soundstage, and I was really hoping the $1000 more expensive CC would be up to the task. That's to say it's narrow or claustrophobic, but neither does it really impress me the way the Atrium did. Well, I think it's time to wrap this one up, and I have to commend Zach and his team yet again. This one absolutely retains the same fantastic build quality that ZMF is known for, as well as providing a comfortable fit and great isolation. Listening to the Caldera Closed is an experience that I will not soon forget, and it was almost everything I had hoped for. Still, I consider falling just short to be a great achievement in and of itself. I'm not sure there's a more impressive closed-back set out there to be found, though that won't stop me from keeping my eyes and ears open.