Fit and Comfort

Seen above is the ZMF Caldera Closed placed on a mannequin head to help show how these headphones would look on the human head. Note that the head is slightly under average sized, so account for the discrepancies accordingly. As with all headphones, getting a good fit and seal is crucial, so make sure to properly use the pivot and rotation capabilities of the ear cups and the height adjustability of the headband itself. This section is mostly a summary of the points expanded upon in more detail on the previous page, but I will point out that the Caldera Closed can weigh 500-560 g depending on the wood, the pads, the headband, and which chassis you go with (magnesium or aluminium). This is slightly above average for closed-back headphones, although fairly typical for planar magnetic headphones with the heavier drivers (more magnets) used. As with its open-back sibling, the Caldera Closed wears its weight very well to where it feels lighter than its actual mass. The headband strap in particular is excellent in providing comfort and spreading that weight over a larger area and the clamp force was perfect for my average-sized head in keeping the Caldera Closed securely fit over the ears. The large ear pads with the fluted shape also help seal nicely to where the Caldera Closed didn't budge at all even when I was purposely shaking my head. Keep in mind that this is thanks to the extensive sizing and ear cup rotation options on hand, which also means it is important to get it set up correctly for you. If you are not used to heavier headphones, then the Caldera Closed may yet weigh you down over time. The mass savings from the magnesium chassis may be worth it thus, although note that the woods used thus far on the Caldera and Caldera Closed have been predominantly denser hardwood, so don't expect much weight savings in that regard from different releases. I'll also point out that, despite the side vents, the Caldera Closed did a good job isolating me from the ambient environment to minimize sound leakage in either direction. It's not the most isolating closed-back set in the world but will do the job at home or a shared office within reason.

Audio Performance

Audio Hardware

I recommend going through this page to better understand the various ideas and components that went into the patented ZMF Caldera acoustic design. Some of this goes back to all those years modding the Fostex T50RP which helped also develop the Atrium Damping System (ADS) which debuted with the ZMF Atrium and is used in the Caldera as well as the Caldera Closed we are examining today. The closed version of ADS is slightly different in that the primary damper is not attached directly to the rear of the driver or to the back of the cup, effectively making it "floating" in the ear cup. ZMF says this also includes segmented diffusion such that the acoustic energy from the drivers is dissipated in combination with the asymmetrical cup design, allowing for more control over back-wave damping and the eventual tonality of the headphones by optimizing the airflow behind and delivering it in a more controlled manner to the ear canals. The closed ADS technology also minimizes standing waves and allows for a more natural decay of sound so that soundstage and timbre still feels natural. The custom-fit ADS is installed underneath the driver which itself is 80 mm in size and is 2 µm in thickness to allow for a good balance of impact and air in the sound presentation. There is a silver coating on the diaphragm to go with gold-plated copper traces which take up a significant fraction of the available area compared to most other such drivers I've seen before. We also saw on the previous page how putting these together is more involved than a typical planar magnetic driver system too!

Then there is CAMS, or Caldera Asymmetrical Magnet Structure, as another integral part of the patented ADS tech implemented here. The N52 magnets are asymmetrically shaped like trapezoids—nine on each side of the diaphragm—to lower the physical footprint along the diaphragm while retaining the magnetic flux to drive it back and forth. This shape, which is similar to a volcanic mountain or a Caldera, is where the headphones get their name from. The magnets direct the increased amount of air and sound towards the ear pads while also diffusing it enough to maintain a uniform frequency response. We've seen various takes on this from others in the past to different degrees of success and have already seen it works well in the Caldera open-back sibling, so I expect to see the same here too with the Caldera Closed. The end result is a relatively easy-to-drive flagship set with a rated impedance of 60 Ω and sensitivity of ~94 dB/mW. A decent solid state amplifier works wonders here, although I did like using a tube preamp too. I understand others have reported tube amps such as the upcoming ZMF Aegis—which releases the same day as the Caldera Closed for a very similar price—to also pair quite well with the Caldera Closed thanks to its variable output impedance settings and the transformer-coupled amplifier architecture.

Frequency Response Measurement and Listening

I will mention that I have a general preference for a warm-neutral signature emphasizing a slightly elevated bass and smooth treble range with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


Our current headphones test setup uses a set of two custom in-ear microphones for the two channels. These microphones closely adhere to the IEC711 class, but have been tweaked to be more reliable in the >10 kHz frequency range, the precise issue with my previous setup, that is otherwise still very good and will continue to be used for IEMs and earphones. Two soft silicone pinnae are installed on the sides, separated by a distance matching my head, and multiple "height" adapters have been 3D-printed for further customization, based on fit, head size and shape. Each set of microphones has an XLR output I separately adapted to 3.5 mm. I used a transparent source—the FiiO K9 Pro ESS—for measurements after confirming it was not a bottleneck in any way. This artificial head simulator feeds the microphone lines into a reference USB sound card, which in turn goes to a laptop that has ARTA and REW running. I begin with an impulse measurement to test for signal fidelity, FFT to test for headphone seal, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/12th setting, netting a good balance of detail and signal-to-noise ratio. The default tuning was used for testing, and no app or program-based EQ settings were chosen, unless specifically mentioned. Each sample of interest is measured at least thrice with separate mounts to account for any fit issues, and an average is taken of the individual measurements for statistical accuracy.


As per usual, you can find my headphone frequency response measurements on VSG.squig.link, along with all the earphone measurements. Scroll to the bottom and choose different targets there, including two from Harman Kardon, developed after years of R&D. Those who have read my headphone reviews would have noted how I typically go for the "Harman Combined" target based off the Harman 2018 over-ear target but with the lower bass target from the Harman 2013 curve instead. I prefer this for open-back sets which it feels far more natural to me, but I refer to the full over-ear Harman target for closed-back sets owing to that bass shelf energy they tend to have. This is not to say that I want headphones to be tuned to this target though—what matters in the end is whether the headphones are tuned with sensible direction and the tonality is executed well. After all, there are always personal preferences and what matters more is how a pair of headphones ultimately sounds to you. First up, take a look at the excellent channel matching achieved here throughout the entire frequency range. Keep in mind that pads and how the set is mounted on the rig also affects measurements, let alone the use of a non-industry standard setup, but I never noticed any imbalance in the ears and this is clearly a prototype unit too, let alone a full retail unit which is guaranteed to undergo multiple levels of inspection on an industry standard rig too. Needless to say, this is the level of quality control and testing that flagship products should aim for and ZMF does not disappoint. I will also mention that using the headphones for over 100 hours didn't change anything either, although I did get new pads in the middle and switched over to those (and a few others) soon after.

I listened to the Caldera Closed and immediately thought this was a more V-shaped sound compared to the open-back version. This isn't to say the Caldera Closed is V-shaped in itself, but more that we have more energy in the bass and upper mids. The former is to be expected from a closed-back set with the ear cup resonances that need to be dissipated carefully. The Atrium damping system helps control this tremendously to where, despite the use of a planar magnetic driver fit inside hardwood cups, there is a sense of decay making me think this is not that far off from high-end closed-back dynamic driver headphones! It still manages to retain that sense of tactility from the planar magnetic drivers allowing for fast mixes to be portrayed effortlessly. House and trance music in particular is a treat on the Caldera Closed. At the same time, and this is something I've noticed a few other high-end closed-back sets do, ZMF has deliberately added in some extra energy from 100-300 Hz and this helps open up the bass, preventing the mid-bass to sound congested in your ears. It also results in punch and impact behind drums and bass guitars—Hotel California and Dua Lipa's "Don't Start Now" are great tracks that illustrate this. The first few seconds of Daft Punk's "Get Lucky" is another case where I became convinced the Caldera Closed is best treated as its own thing as opposed to just a closed-back version of the Caldera (open). The dynamic range here is again something I haven't experienced from planar magnetic drivers yet, at least out of the box.

Indeed, where I thought the thicker mids of the Caldera were quite a statement, the Caldera Closed ends up being somewhat lean to my ears in the lower mids. It's partly from the bass shelf but partly also from the upper mids/ear gain starting off earlier than what I personally prefer to come off more forward simultaneously. The end result was string quartets and baritones not getting the love I'd have like to see. I found that turning down the 1 kHz region by 2 dB helped tremendously, now I had a wider soundstage too and the sense of imaging spread to a wider cone in the front of the head. The mids of the Caldera Closed will be an acquired tonality in either case depending on not only the base tuning, but also your HRTF, the pads/mesh used, and even how you orient the pads around the ears. It's the trickiest section to describe as a whole, especially when I know the frequency response measurements seen above don't exactly capture the upper mids as I perceive them. You see, I felt there's more ear gain than the graph above suggests and it's centered around 2.5 kHz, but still starts earlier than usual. It then gets lower before a small peak at 6-7 kHz leading to the treble. The net result was ultimately great for female vocals as a whole, and less so for male vocals that can come off slightly muddy/recessed.

The treble is another strong point for the Caldera Closed, especially with the deliberately relaxed-yet-extended signature unlike anything else I've used. ZMF believes that a slightly darker sound in a closed-back set can help make it less fatiguing over time, as well as for those suffering from tinnitus. I agree on both fronts as long as it does not impact detail retrieval too much. In this regard, I do see some compromises being made with the individual notes of string quartet not as easily identified as some other flagship sets, but the end result is this is a planar magnetic closed-back set I could listen to for hours without tiring my ears or even feeling there was any pressure build-up inside. There's no sibilance and I also appreciate the air in the higher frequencies—again not as emphasized as my measurements make it seem—resulting in a larger sense of space, especially for harps and piano tracks. The low-pass filter we saw cleverly implemented in the driver assembly results in a deliberate cut around 12 kHz which helps with the overall effect and is something that ZMF should be proud of.