ZMF Caldera and Atrium Closed Headphones | REVIEW

zmf caldera

The ZMF Caldera and Atrium Closed headphones arrived at a fortuitous point in my reviewing schedule. I had just purchased the Naim NAIT 50 integrated amplifier for use as both back-up amplification and as a dedicated headphone amplifier. In addition, when I returned the Aretai Contra 100s speakers to Gary Alpern at True Audiophile in Portland, he asked me if I wanted to check out the Audion Silver Night 30th Anniversary headphone amplifier which uses 300B tubes in the output stage. I’ve had a hankering to play with some 300B tubes for quite a while now, even if it was just for headphone use.

Words and Photos by Marc Phillips

At the same time, both Scot Hull and Brian Hunter had been speaking with Zach Mehrbach of ZMF–Scot had listened to ZMF at the Chicago CanJam a few months ago, and Brian’s already reviewed a pair of the ZMF Atriums for AudioHead. Both are quite enamored with these gorgeous cans (lasciviousness not intentional), and they turned to recruit me into their cult. I went along without a fuss.

I’ve been threatening to put more headphone coverage into Part-Time Audiophile, and here I am, in my new digs, with a solid oak coffee table left behind that serves as a nice surface for a headphone rig, and plenty of isolation devices from Les Davis Audio, Fern & Roby, IsoAcoustics and Carbide Audio to reduce any vibrations. When the ZMF Caldera ($3,499) and Atrium Closed ($2,499) arrived, in a box that seemed way too heavy to merely contain two pairs of headphones, I looked at my new head-fi empire spread out before me and told myself ah, this is going to be fun.

zmf caldera

Inside the ZMF Caldera and Atrium Closed Headphones

Why was the box containing the ZMF Caldera and Atrium Closed so big and heavy? Each headphone comes in its own gorgeous box–the Atrium Closed in a matching wood case and the Caldera in one of those durable flight cases that every high-end audio component over $1,000 should include. Plus, you get all of the cables with various terminations, and finally extra earpads so that you can customize the fit.

In fact, there were a lot of earpads in the box. Maybe all of them, I don’t know. I’m sure they were included so that I, the audio reviewer, would find the ultimate match with my cranium, so I’m not sure how many the average customer receives. As Zach told me, “The Caldera comes with that mantle mesh and a plethora of pads and I know that can be confusing, but we try to make the headphones modular in both sound and design.” I did figure out rather quickly–both the ZMF Caldera and Atrium Closed are fairly heavy and bulky headphones, and finding the perfect earpad makes all the difference when it comes to maximizing comfort and minimizing listener fatigue.

Zach went into more detail:

“WE have a plethora of top pad options, may be worth mentioning that this part of the headphones is modular as well, we have a video to show installation. Only other note is that the lighter ZMFs have magnesium chassis and black/coffee gold aluminum grille or rods. So the weight can be down towards 400-450 grams on lighter sets.”

The Atrium Closed headphones are, obviously, a closed design, which made me a bit concerned because I’ve come to the conclusion that open headphones are more my thing–I always want that extra spaciousness so that I don’t feel claustrophobic if I wear them too long. (There is an “open” version” of the Atrium.) But I also understand the need for closed designs–on airplanes, for example, or in a crowded home or office with lots of people mulling about. In fact, I was tempted to bring the Atrium Closed headphones with me on my recent journey through Western Europe, where I had to catch almost a dozen flights before I could return home. But there’s something about ZMF headphones that seem far too nice for wearing in public. I certainly didn’t want to drag them into an airplane bathroom with me. Blech.

zmf caldera

Zach Merhbach knows this:

“With Atrium Closed, we explored the versatility of an enclosed atrium through segmented airflow. By diffusing the airflow on each side of the driver, and by creating separate cavities around a diffuser within the cup, Atrium Closed imparts a natural, vast, yet isolating sound.”

The ZMF Atrium Closed headphones design is also summarized in depth on the website:

“Utilizing the natural presentation of ZMF’s proprietary Atrium 300 ohm Bio-cellulose driver, The Atrium Closed has a fresh take on ADS damping and introduces the concept of gradual diffusion through multi-weighted materials and zoned sonic diffusion. ADS for closed headphones was developed in concert with the Atrium Open to address the joy of owning a closed headphone that isolates completely, provides satisfying sub-bass rumble, and has the musical linearity for any content in your collection.”

The ZMF Caldera headphones, on the other hand, are an open design, and they represent ZMF’s first foray into planar magnetic drivers:

“After modding, breaking, and completing hundreds of Fostex t50rp mods over the years I spent a lot of time staring at planar drivers. I tried experimenting to make the drivers sound effortless, dynamic and resolving. When modding though, I was always starting backwards, reverse engineering a driver someone else created. I dreamt of making my own “from scratch” planar driver when ZMF transitioned to dynamic driver headphones, but with so many amazing planars out, I didn’t want to be reductive, or redundant. After a lot of failed experiments, and over 6 years of trying, the Caldera driver, CAMS (Caldera Asymmetrical Magnet Structure), and Atrium Damping System; the magic of ZMF’s proprietary planar technology has been born.”

The ZMF Caldera is also the reason why Zach sent so many earpads. “The Caldera pads are fluted from inside out,” Zach explained, “channeling the path to the ear for airflow that starts at the Caldera membrane.” These earpads feature a semi-vented air-flow with an asymmetrical angled design that becomes an integral part of the whole design.

Finally, the ZMD Caldera and Atrium Closed headphones are special due to the wood used in each product. This is what sets these cans apart, other than their sound. All ear cups are CDC-machined, and you do have a choice of woods–although Zach warns that custom products with exotic woodwork can take a lot of time, and suitable wood may be difficult to find. This is why ZMF creates so many limited edition finishes and holds annual sales to refresh the inventory.

atrium closed


As you might imagine, my new headphone rig was just as complex as the last “serious” one I reviewed, with smallish components from Ferrum Audio and Ideon Audio powering a pair of Focal Clear MGs. I loved that rig, and thought at the time that it was the finest sound quality I’ve heard from headphones. This new rig, with the ZMF Caldera and Atrium Closed headphones, and several dedicated headphone amplifiers, had all the potential to meet if not surpass that other rig.

Here’s how it ultimately mapped out. The ZMF Caldera and Atrium Closed cans were powered by three headphone amplifiers: the headphone amp inside the Naim NAIT 50 ($3,699), the dedicated Audion Silver Night ($4,995) and a new contender that snuck in the last second, the Austin AudioWorks The Black Amp ($1,649), which has been designed by Barry Thornton.

The main sources I used with the ZMF Caldera and Atrium Closed were my Unison Research Unico CDE CD player, which has served me well for a dozen years now, and the Innuos Pulsar network player ($7,999) hooked up to the Merason DAC-1 Mk.II DAC ($8,000). Cables varied according to system configuration, of course–the Naim required the use of a Moon Audio Blue Dragon 5-pin to RCA interconnect, while the Audion allowed me to use everything from a pair of Furutech NCF RCA interconnects to the mighty AudioQuest Firebird XLRs. Power cords were also dependent upon the components, especially since the Naim NAIT is designed to be used with the included Naim power cord–I was a Naim guy for many years and I know it’s not a good idea to use big, heavy power cords on this finicky British gear. (I bought this, so I don’t want to void any warranties.)

As you can see, the ZMF Caldera and Atrium Closed headphones were in excellent company, and I was eager to get started.

ZMF Atrium Closed Sound

I started off with the ZMF Atrium Closed, mostly for that can-in-get-any-better-than-this effect once I swapped for the ZMF Calderas.

If I had any reservations about the ZMF Atrium Closed, it was–somewhat predictably based on my biases–my wish for the sound to open up just a li’l bit more. As I disclosed previously, that’s sort of my reaction to the whole open vs. closed debate in headphones. But I also have to admit that no closed headphones I’ve heard come close to the Atriums in terms of tonality and frequency range.

The ZMF Atrium Closed headphones, however, immediately impressed me with their sheer sense of bass slam. For instance, on Kane Mathis’ Geminus I immediately noticed that I was able to absorb more of the deep bass information and bask in the tightness and organization of it all, especially considering that all of the lower frequencies were created by acoustic instruments. That means the bass shouldn’t be exceptionally deep, but there should be a lot to it–quick and explosive transients, lots of decay, and that extra energy cheerfully supplied by a slap of the hand on a drum skin.

The Atrium Closed headphones were also detailed without being forceful about it, an important consideration when listening to headphones. (It’s so easy to get overwhelmed by tons of sonic information, hastening the sense of listener fatigue.)

One thing I did notice in regards to headphone amps–the Atrium Closed seemed to prefer running through the Naim NAIT 50 inboard headphone amplifier than the Audion Silver Night. Perhaps that’s because the Audion and its 300B tubes offers such a smooth, liquid sound that I thought I was getting a little too much of a good thing when it came to a euphoric, easy sound. The NAIT 50’s headphone section is more neutral and linear and gives me a more transparent view into the recording. But before I blame the Audion for doing something “wrong,” I must admit that the ZMF Caldera absolutely loved the Silver Night.

ZMF Caldera Sound

Zach describes the ZMF Caldera like this: “Hearing the Caldera for the first time is an experience like no other, and we’re excited to take that hike up the mountain with you.” That’s exactly how I felt the when I switched from the Atrium Closed to the ZMF Caldera.

From the first track I heard, the ZMF Caldera quickly asserted itself as the headphone genie who wanted to grant all my wishes. The Calderas were open and warm yet not too warm. Those Focal Clear MGs I enjoyed a couple of years ago certainly captured my heart in an immediate way, and the proper amount of warmth was key to my ultimate appreciation.

The ZMF Caldera, however, sounded closer to what I would hear from a highly-resolving two-channel system–unlimited detail, astounding bass performance, and even killer imaging and soundstaging, albeit inside my head. The longer I listened to the Calderas, the less I could criticize the overall sound, and by criticize I mean taking the side of those audiophiles who would much rather listen to that two-channel system with the big loudspeakers. In fact, I could quickly alternate between my two-channel system and the headphone rig, which are now in the same room, and I never felt I required a period of adjustment. Both systems sounded like music, and I stopped thinking about it.

atrium closed

Listening Sessions

When it comes to reviewing headphones, the listening sessions are more important than anything else. Why is it different from reviewing other types of gear? Because a headphone listening session should be less of a casual event, and more of a carefully planned sojourn through all your favorite types of music.

For me, it’s all about curling up on my sofa and completely losing track of the time. Maybe falling asleep a few times, maybe waking up because something caught my attention. I want to be isolated from the world. I want to forget it exists. I want to lose myself. That happens, of course, when listening to two-channel hi-fi on a pair of speakers. But headphones make it so much easier because you’re entering into your own little pod of bliss.

This is where the ZMF Atrium Closed headphones showed off their biggest strengths–isolation. I felt that the ability of the Atriums to connect more directly to my brain, unfettered, was an intoxicating reward for dealing with a hectic life. The closed design allowed me to concentrate on the deepest and darkest corners of each recording, exploring spaces and finding those magical moments where you notice something for the very first time.

The ZMF Caldera, on the other hand, was purely about the music. The Calderas were a vacation in my living room, offering the type of balanced sound that checked off every conceivable box I could think of–a natural tonality, an extended frequency response and a comfort level with the right earpads–and it surpassed any other headphone rig I’ve tried.

This is where the Innuos Pulsar network streamer, along with the Merason DAC-1 Mk.II DAC, came in. In the past, my headphone sessions were always interrupted by the swapping of physical media. Not when you’re streaming Qobuz, my friends. I’ve been grumbling about how busy my year has been, with a lot of traveling that’s taken me away from the joy of reviewing high-end audio. I was downright ecstatic at the invitation the ZMF headphones offered every time I walked past the headphone rig in the living room. Come, sit down. Forget your problems. Listen to how far headphone technology has come in the last few years. Listen to Chocolate Chip Trip until you pass out.

What a gift this headphone rig has been over the past few weeks. I have the best job in the world.

ZMF Caldera and Atrium Closed Conclusions

If this review feels somewhat incomplete, there is a reason. Both the ZMF Caldera and Atrium Closed headphone are among the finest I’ve heard anywhere, and I discovered that they are both an ideal tool for reviewing headphone amplifiers. If my 2023 reviewing schedule has had a theme, it’s “The timing is always off with all of this gear.” I bought the Naim NAIT 50 so that I would always have a headphone amp around so I could review more headphones. What happened? A plethora of headphone amps have arrived–the Audion, the amazing little Austin AudioWorks The Black Amp and the latest headphone amp from Enleum.

My time with the ZMF Caldera and Atrium Closed was coming to an end, and I felt anxious that I would send them back and have to procure another pair of review cans that could somehow come close to this level of performance. So I spoke with Zach Mehrbach and he’s been generous in letting me keep both headphones for a bit longer to evaluate all these amps.

To me, that says something about ZMF. While it seems like I harped a little bit too much about the Atrium’s closed design, in truth I’ve never heard a pair of closed cans that offered this type of detail, bass slam combined with such a relaxed and truthful presentation. I hope it doesn’t come off as damning with faint praise when I say I’ve never heard a closed design that offered this much. To me, my appreciation of the Atrium Closed is noteworthy.

The ZMF Caldera, however, might just be my headphone soulmate. For me, the Caldera impressed me more than any other headphone I’ve used. I don’t have the seat time with other headphones at its price point, but I’ve also been listening to decent headphones since I was a teenager back in the ’70s. (I’ve also attended enough CamJam events to audition just about every “hot” headphone on the market.) So the ZMF Caldera sets a high bar for me personally, and by a large margin. They get my highest recommendation.

  • Impedance: 60 Ohms
  • Driver: 80mm with CAMS Patent Pending technology
  • Weight: 490 – 550 (weight varies depending on Chassis)
  • Sensitivity: ~95dB/mW
  • Oak Caldera
  • ZMF Stock Braided Cable and OFC Cable
  • ZMF Caldera and 1 set of your choice
  • ZMF Owner’s Card
  • Lifetime Driver Warranty
  • Impedance: 300 Ohms
  • Driver: Biocellulose N52 Atrium Tuned Driverr
  • Weight: 480g ± 30g (aluminum chassis, black grille/rods)
  • MAG Chassis reduces weight by 34g
  • Sensitivity: ~96dB/mW
  • Cherry Atrium
  • ZMF Stock Braided Cable and OFC Cable
  • ZMF Caldera thin (Lamb) and Caldera Suede pads
  • ZMF Owner’s Card
  • Lifetime Driver Warranty

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