Closer Examination

Every retail purchase of a ZMF Caldera will come with two included headphone cables. You get a choice of 3.5 mm/6.35 mm (1/4") single-ended as well as 2.5 mm/4.4 mm/4-pin XLR balanced connectors to work with and the decision to make is which one will be on the stock braided cable which sells for $60 as-is and which the more expensive OFC (oxygen-free copper) cable will have. As with the ear pads, you choose the cables from a drop-down menu on the Caldera Closed product page so logically you'd go for the more expensive cable to have the connector you will be using most. Things may not be that simple in practice though! The cables provided with this review unit are the stock braided in 4-pin XLR and the OFC in 6.35 mm and the latter is stiffer than I would like as a result of the thicker 24 AWG copper strands with aluminium and copper shielding used—ZMF also sells braided OFC cables in addition to more expensive and fancier cables which you can also order alongside the headphones. The OFC cable is certainly more durable than the stock braided cable though, so it has its use in more professional environments. Both of these cables use copper conductor regardless, have ZMF-branded splitters—different design, could be different ODMs—and are black in color to be a fairly safe aesthetic choice. The split cable now leads to two mini-XLR connectors that come with heatshrink to work as strain relief and L/R markings on the metal housings to help indicate the left and right channels, respectively.


When I opened the case these headphones came in, I was expecting to see the stock wood finish on this review unit as with the Caldera demo unit form before. If not that, then perhaps the limited release using the Shedua wood. I was not ready to see something else entirely, and then I remember this is a prototype model made for testing and reviews so ZMF no doubt had tried a few different wood types to see what works best. We'll talk more about the ear cups shortly, but allow me to point out how the various components that undergo typical wear and tear are designed to be easily replaceable in this modular design, thus allowing longevity as well as allowing customers to play around with them to get the comfort and tonality to their desire. The headband assembly, for example, is called the ZMF crescent strap and it worked really well with the Caldera previously to where I am sure this will be quite successful in comfort and clamp force this time too. There are foam inserts on the underside of the headband to help better distribute the weight across the top and sides of your head while still having room for airflow. The strap underneath smoothens it out further and has the ZMF lettering embossed on it as well as on the outside on either side—don't worry about the different writing on this prototype. There's a steel band in the curved section by default and you can choose to get this in leather, as seen above, or vegan suede.


The headband installs with screws into the frame which is made of aluminium or lighter magnesium at a $200 premium if you so choose; this sample has the default black anodized aluminium. On the inner side we also find L/R markings to help indicate the left and right sides of the headphones, respectively. The yoke rods are black by default—they will be coffee gold in the LTD version if the photos I have seen online are anything to go by. There are several discrete notches allowing for easy vertical sizing as well as removing any ambiguity over whether the two sides are matched up or not. The tensioning of these rods can be adjusted using the tiny screws on the side, in case you find them somewhat loose over time. As seen above, there is plenty of sizing to allow the Caldera Closed to fit over heads small or large alike.


Those yoke rods also act as pivot points allowing the ear cups to swivel freely. Add to this the rotation upwards and downwards as usual and there is so much freedom of movement in all three axes to pretty much guarantee you get a great fit around your ears.


As the name suggests, the Caldera Closed is a closed-back set and thus we don't see an open grill as typical with open-back designs. The Atrium Damping System used here involves airflow and careful venting which is why we see side ports on the ear cups. I made sure to mention this right away because, if you are anything like me, your eyes will immediately be drawn towards these gorgeous Queensland Maple wood ear cups on this review sample. Queensland Maple is sadly not one of the available wood options for the Caldera Closed at this time, although you can get the Atrium Closed LTD in it as of the day I write this review. This is an Aussie wood, although the specific source of the wood used here is Hawaii, and is closer to citrus trees than maple if we were to be pedantic. The wood is extremely hard to source and expensive as a result, although well worth it with how lustrous and rich it looks once it has undergone the ambered UV gloss finish which has made me a believer in wood chatoyance for good. This is why I broke out the black backdrop as well as taking it outdoors in the sun, thus allowing you to appreciate the ZMF handiwork in more detail—especially since this is such an important part of the retail ZMF experience. Expect to see different wood releases over time, as well as stabilized/resin versions in special batches and colors which will all be unique.

Another thing you will note here is the fairly unique shape of the ear cups. When I first saw the Caldera Closed prototypes shown off at audio shows, I thought perhaps there was some inspiration being taken from the Sony MDR-R10 headphones akin to what HIFIMAN and a few others have done since. But in fact the concave angular ridge on the side is intended to be similar to the heel on the handle of many musical instruments, providing a natural and comfortable real estate to hold the ear cups on to when placing the Caldera Closed on/off your head. This also contributes to the sharper triangular lines on the top that is somewhat similar to a volcanic cone to match the Caldera name, and this results in a deliberate pattern which is different from the other ZMF closed-back sets. This particular sample does not have perfectly aligned ear cups—it's a prototype for a reason, retail units will be fine—else I would have also taken a photo of the ear cups together to show you how it collectively looks like a volcanic crater in the middle. Another likely explanation for why ZMF went with this more intricate design is to simply make it harder for copycats; I've found there are multiple such people selling their wares on Taobao/Aliexpress. Regardless of the reason behind the design, I suspect the end result will be divisive though as the shape and lines can range from being more obvious on the stock Shou Sugi Ban Ash wood if the burnt lines clash with the wood grain and meld in more with other woods that don't have the charring or different grain alignment/wood patterns, such as this very prototype and the Shedua LTD version. So depending on your preferences, you may want to choose the Caldera Closed version accordingly or wait for future releases. I understand ZMF can accommodate some slight wood characteristic preferences too, so it is also worth talking to them first.


I also knew going in that the Caldera Closed will use ZMF's own Caldera ear pads, which are contoured pads that have specific left and right sides. The stitching line on the pads is aligned with the cable connectors to make it easier when pad swapping, although you may want to play around with the pad alignment regardless depending on the fit/seal as well as the sound presentation achieved. The ear cups have machined grooves to accommodate the ear pad sleeving that is flexible enough to stretch over and fit into said grooves for installation as seen above.


Removing the stock ear pads shows a pre-installed tuning mesh which is installed on a red exterior that has holes in it to help align the entire assembly over the screws that secure the planar magnetic driver used here. The color also helps identify the mesh given the optional lighter mesh is all black as we saw before. Then we see the same carbon fiber baffle used in the open-back Caldera for weight reduction, and it is secured via screws to the cups and the driver assembly to the baffle itself. After all testing was completed, I got the greenlight from ZMF to disassemble the headphones and I decided to get a closer look at the driver—the exact same as used in the Caldera open-back set—as well as the patented Atrium Damping System underneath and a PCB all the way at the bottom which is a clever low-pass filter we will talk more about on the next page. You can also see here how the ear cups are truly machined of the wooden block as opposed to using a thinner sheet or veneer as with a few other brands. I also found it interesting that ZMF has a geometric pattern on the inside despite no one being able to see it.


At this point, we can also have a closer examination of the stock ear pads which are hybrid in design in that the inner lining is made of suede and the rest of the outer surface is premium lambskin. You can also choose to have vegan suede pads instead, and there are other optional Caldera pads recommended for the Caldera Closed as we will discuss in detail soon enough. These hybrid stock thickness pads are perforated on the contact surface and solid on the sides to have a balance of airflow through the pads but with controlled diffusion as from a solid pad. The inside has stiffer-than-average gel infused slow rebound foam, the pads are more oval than round with 110 mm spacing at the widest point and closer to 104 mm on the other side, a 72 mm ear cavity, and thickness going from 20 to 25 mm from the thinner side to the thicker one. The full name for these pads would likely be "Caldera Stock, Top Perforation, Hybrid" and I am choosing to refer to these as "Caldera Hybrid, Top Perf." for convenience as well as to avoid making the pads discussion a mouthful. The ZMF team will have a challenge on their hands soon with a lot of different Caldera pads to be named and differentiated by material type, thickness, and perforation extent—especially with the decision to rename BOKEH pads to Caldera pads as well.


On the bottom of the ear cups, towards the middle where the pad stitching lines up, is where we find the mini-XLR cable connectors jutting out slightly from the surface of the cups. Connecting the cable is simple in that you simply align the alignment/locking pin in the cable-side connectors to the opening in the headphone-side connectors and push until they lock in place. Removing them is even easier and involves pushing the locking pin inward while pulling out the cable. Depending on the cable you have and the connector type chosen, you can get different lengths and your choice of single-ended or balanced connectors on the source side—these then head over to your headphone amplifier as usual. The nature of the Caldera Closed headband means you may have some pressure on it when using a headphones stand—ZMF says the high quality leather will withstand said pressure without issues—and I recommend against going with one of those omega-style stands that may add unnecessary wear to the ear pads.