Fit and Comfort

Seen above is the ZMF Caldera 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 can weigh 480-560 g depending on which chassis you go with (magnesium or aluminium), which is on the heavier side of average for headphones but not that far off from your typical planar magnetic set. Some of this mass is from the wooden ear cups so note that going with a limited edition Caldera using different wood/resin compositions will also change the overall weight. Likewise, different ear pads and the vegan suede headband will also have a small effect, but in general I'd say the Caldera wears its weight very well. 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 securely fit over the ears. The large ear pads with the fluted shape also help seal nicely to where the Caldera almost became an extension of my head and didn't budge at all even when I was purposely shaking my head. Over time that weight can get to you if you are not used to heavier headphones though, so either take a break from time to time or consider saving up for the magnesium chassis for what should be a significant change compared to this aluminium version I have here. The ZMF Caldera is an open-back set so the usual caveats apply about best being heard in a quiet environment, although it doesn't have as much leakage as most planar magnetic sets I have here—could be the thick pads doing their job.

Audio Performance

Audio Hardware

I recommend going through this page to better understand the various ideas and components that went into the patent-pending ZMF Caldera acoustic design. Some of this no doubt 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 here too—behind the grill, in fact. This allows 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. You can see the custom-fit ADS installed on the carbon fiber baffle in the first photo above. Then we get to the driver itself which is 80 mm in size and thick enough to allow for balance of impact and air—ZMF keeps the actual thickness a secret but does let us know 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—more so than the vast majority of other such drivers I've seen before.

This is made possible by the use of CAMS—ZMF loves its acronyms clearly—which stands for Caldera Asymmetrical Magnet Structure and is part of the patent-pending 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. In particular, the magnets direct the increased amount of air and sound towards the ear pads while also diffusing it enough to maintain a linear frequency response with punch. We've seen various takes on this from others in the past to different degrees of success and will soon see how well it works here. This shape, which is similar to a volcanic mountain or a Caldera, is where the headphones get their name from. Think of the immense air blowing up linearly from a volcano with impact behind it and the analogy works further. Regardless, the end result is a relatively easy-to-drive set with a rated impedance of 60 Ω and sensitivity of 95 dB/mW. A good solid state amplifier works wonders here although I had a great time pairing the Caldera with a few tube amps such as the Feliks Audio Echo II and Envy as well as hybrid amps with a tube preamp stage such as the HIFIMAN EF1000.

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 at the end of the day there are always personal preferences so this is where what matters more is how a pair of headphones is tuned and how it ultimately sounds. 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 random demo unit as opposed to a cherry-picked one. Needless to say, this is the level of quality control and testing that flagship products should aim for but so far it feels most others are happy with the industry standard +/-3 dB variance. 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 haven't listened to enough from ZMF to tell you what the ZMF house sound is, but if it's a thick and impactful sound that still feels in control then the Caldera can be a poster child for demonstration. Indeed, the first thing which came to mind is this isn't like most planars on the market. If you are worried about a bright, potentially fatiguing treble presentation which can make the mids feel relatively lean mids—especially compared to a high-end dynamic driver set—then the ZMF Caldera might just be what the doctor ordered. All that tech used here as well as the new pads come together to put out a focused sound that I initially wasn't expecting and ended up liking more and more over time. Having listened to a few different Caldera units at the show, especially with different wood cups, also showed that the bass and mids can come off tighter with a more dense wood although the stock oak helps with tonal balance and making sure the mids are the star of the show. With the stock version, bass is well extended with a slightly soft sub-bass to where those whose music library consists primarily of electronic music may want to play around with EQ—distortion is low enough to allow plenty of EQ room—or even look at other options. Where the Caldera really shows off is in the mid bass and mids proper with good impact and body to the tones which reminded me of the HEDDphone TWO with its AMT drivers. It's not as fast sounding—think decay and transients—and perhaps the damping system is deliberately having control here where the Caldera also reminded me of the Focal Utopia with its dynamic drivers. I'll also put in one more immediate comparison here, despite having a separate section dedicated to it, and say my experience with the ZMF Caldera was similar to that of the Meze Elite with its warm, mid-forward presentation. Suffice to say that the Caldera has fingers in many pies and somehow manages to eek out a winning formula regardless.

The Caldera is dynamic and punchy but does not feel like a night club is thumping in your head. It's very detailed but not overloading you with information lest it be fatiguing. It allows for instruments to get their time and allow the next entry in line to come in allowing for good contrast and separation. Layering is excellent thus as is imaging. Brass instruments sound lively as do drums—you'll feel the snare hit on well recorded tracks. The slight dip and subsequent rise in the upper mids allows for some sizzle and bite to guitars too, which is interesting since usually this has only resulted in nasal vocals for me before. Speaking of which, I will say instruments seem to take second place to vocals in general. Old school rock is a great fit with the Caldera, as will be heavy metal with grunting low pitch male vocals and electric guitars. The ear gain comes earlier and feels more prominent as a result of the 1 kHz dip as well as higher than what the measurements may make it seem. But I was fine with it. given my HRTF tends to work well with a prominent ear gain anyway, and the dip thereafter is also true in that it helps prevent female vocals from sounding honky. Somehow this ends up making for instrument timbre which sounds more correct than most planars, although not as natural sounding as some dynamic driver sets. On the other hand, one side effect of this tonality is it can be more revealing of vocals and piano keys—think sopranos in an opera as well as some of Chopin's tracks which may not have been mixed well. The Caldera with its increased resolution can also accentuate faults to where it may come off like a mixing set for a highly specific niche despite it being more an audiophile set.

Another side effect is the soundstage which is harder to describe since I don't have a specific consensus on it. With my acoustic jazz and pop library it generally came off fairly wide and deep but on others less so—orchestral recordings with more string instruments felt slightly cramped. Perhaps this is to do with the more relaxed approach taken in the upper mids and treble alike. The plus side is you won't want to rip out these headphones ever given no sibilance or fatigue, although there is some upper treble presence which can go from being sparkly and airy for some to potentially annoying if you are sensitive here. I suspect this is also a contributor to the soundstage as well as the increased detail retrieval despite maintaining clearly thick mids. It may not seem that different simply from the graphs but boy does the Caldera sound unique and in a generally good way too.