This is just going to be "a couple days of use" set of impressions and some measurements. Don't consider this a full review.
First, off I received this demo from Zach the other day and I had posted my first impressions after just an hour of play. I will say that the "spiciness" that I was hearing seems to have waned off a little bit with the default Caldera leather pads that came attached with the unit. The Suede pads smooth it out even more, though with those pads, there is a small bit loss of some of the intricacies and agile-transient response I hear with the normal pads. I also tried the thin cowhide pads, but I did not like them much for my own tastes/music, and basically put them away after I measured them afterward.
For those who are interested in pad measurements, I'll post those at the end here, along with a comparison to the Susvara, which is my favorite, and normal headphone I use when I want to listen to music on headphones at home.
I spent a good chunk of my first day and half listening to the Caldera on my iBasso DX240 DAP with Amp 8 MK2. I used a 4.4mm to XLR adapter and listened to it on that, as well as just listening to it on the single-ended output. I found the Caldera to have no issues with this portable source. I then took the Caldera for most of last night and today and plugged it into my normal listening setup of the Holo Spring 3 KTE and Bakoon AMP-13R through my Roon Core dedicated server PC. This opened up the quality quite a bit, with more depth, and improved resolution, and just opening up the overall sound in general. In my photo, I also have the new SMSL DO200 MK2 DAC, which was also sent to me for a review, and I've listened to it briefly with the Caldera, but I prefer the more engaging Holo Spring 3 in general.
I also compared it to the Hifiman Susvara on both source setups, and same general opinions on the source synergy. Susvara, as you know, needs quite a bit of current to get it to drive correctly, and just to get it loud. For reference, I had to double the volume output on high gain on my DAP to get it to the same listening levels.
Caldera General Impressions
I had a nice email exchange with Zach the other night sharing some music suggestions back and forth as we found out we share some common fondness for progressive bluegrass and indie folk music. For those who are interested in what type of music this is, I recommend checking out the Country Coffeehouse playlist on Spotify (I ported this playlist over to Qobuz/Roon for my listening here), and check out bands like Crooked Still or Andrew Bird, or stuff like that. I also listened to a bit of piano jazz music from artists like Bill Laurence, GoGo Penguin, and Tingvall Trio.
For this type of music, I really like the tuning that the Caldera brings with the more forward upper mid-range and treble, that I think sometimes is missing some prior ZMFs. The Atrium is another one that I think does this really well. Of course, making this go too forward can make it nasally sounding and I think the Caldera can hover that line on the default pads, with the Suede pads smoothing this out a little more as I mentioned before. The cowhide thin pads that I briefly tried remind me of of how Verite sounded when I owned it, but it's been a long time now since I parted ways with it, so take that with grain of salt.
The Caldera, to me, is fairly neutral sounding, with an elevated bass region that provides more body and meat to the bones than, say, my Susvara and other Hifiman planars. In this comparison, Hifiman-house sound is thinner and more focused on speed and attack, where I find the Caldera is more focused on being powerful and thicker, with a sound that has that traditional ZMF sound on the dynamics, but with the added agility and attack that the planar drivers typically bring. For the most part, this headphone reminds me of a Hifiman with a warmer and more bass emphasized sound. I prefer it over typical Audeze sound, and to me, it brings together the best of both worlds -- an Audeze-like low end mixed with the mid-range and treble of a typical upper-tier Hifiman (i.e. not too bright, but smooth sound of the Susvara, HE6-series, etc.)
In a direct comparison to the Susvara:
The Susvara is still beating the Caldera in resolution and speed. While the Caldera is meatier and thicker with a more balanced sound, I do find the Susvara to be overall smoother, with a more ethereal sound that is little more refined. The Caldera has more "dynamic driver" qualities to me than the Susvara does, if that makes sense. Both of these have quite similar general sound balance outside the slightly more elevated bass response of the Caldera.
I think the Caldera has a good soundstage and also good layering and depth. The Susvara is stretches a little wider and deeper. It has a more grand sound than the Caldera. I enjoy both for different needs. For orchestral and jazz music, I like the Susvara a lot. For rock and this progressive country music I talked about earlier, I like the Caldera quite a bit too. Both do all these genres well in my listening experiences so far.
I haven't compared the Caldera directly to my Sennheiser HD580 and HD600 yet, but I can see some similarities here too, in terms of tonality, but with a better soundstage and resolution. The Caldera kind of fits somewhere between the Susvara and those two for me in overall qualities (though leaning closer to the Susvara for some of the very critical listening things like detail retrieval).
Anyway, I don't know where I am going with this anymore. I don't think the Susvara and Caldera are necessary competitors, though it's hard not to compare them. For my personal tastes and enjoyment, I can see both being very good compliments to each other.
More to come.
Now for the measurements I took. I use an IEC-60318-4 coupler with a flatplate and ear pinna that somewhat simulates the GRAS 43AG, however it is still a clone. I have a compensation file that I use to make it as close to that as possible and I've been very happy with how my FR graphs have turned out over the past couple years that I've used this over-ear system.
This first graph is of the three pads that came with this unit. The blue line is the default Caldera pads, while the red is the Suede (thick), and the green line is the Cowhide.
This second graph is a comparison to the Hifiman Susvara, in yellow. I removed the cowhide pad from this comparison as it measures a bit differently. I don't want to go too deep in the squiggle interpretations, but I hope you take a read through my audio listening experience above before really going over the graphs. Remember the lines are normalized to a specific frequency (in this case, 800Hz), and you need to look at the lines relative to themselves too as a whole response (i.e. Caldera bass may not show that its more elevated in this graph, but in my listening experience, it definitely has a warmer and thicker sound -- which maybe attributed to the less elevated treble range, when compared to the Susvara)
Matched at 1KHz -- (you'll see the bass levels are show it higher on the Caldera than the Susvara with similar treble levels)
Feel free to ask me any questions you have on either my impressions, squiggles or both. I'll post something more formal later when I have more time on these headphones, but this is probably going straight towards the top or near the top of my ranking list at this point. I really like what I am hearing here.