Caldera

Probably the Caldera is closed in the office. I actually prefer it to the Caldera open that I have at home lol Probably bc I’m less distracted in the office, and can properly concentrate on the subtle qualities of a headphone. At home. I tend to mostly use the HD800S for general use and gaming (flight sims, and some BF6). Because it’s light, it works well with my head tracking gear. For music, coming out of a class-A solid state (Cayin IHA-8), I find them to be kinda sterile and boring tbh. For music,  tend to reach for the Caldera open and the Atrium the most. My Solitaire P should be my most technically accomplished headphone in my collection. But TBH I’m not a fan of their tuning. Thinking of selling it (I got mine second hand, for around 20k rmb), and getting a He1000 unveiled. Or maybe a Susvara Unveiled, if I find one for 30k rmb. Which would hopefully stop me from buying any more headphones lol

From everything I have owned and heard, I would elect three headphones as my overall best and favorites: the DCA E3, the ZMF Caldera Open, and the Audeze LCD-4z. The E3s excel with raw precision and separation, the Calderas with spatial flexibility, tonal transparency, and macro dynamism, and the 4zs with bringing a bit of every trait together into one package. All of these need EQ to sound their best, the E3s the least and the 4zs the most, but even a profile relatively close to neutral reveals each to be amazing in their own ways. For anything below $1000 used, my picks go to the 2021 LCD-2 (and X), Moondrop Cosmo, and Sennheiser HD 800 (also all with EQ).

Congrats, those Atriums are a real stunner! The headphones that ZMF use natural wood finishes for continue to be among my favorites that they make, despite how good a lot of their stabilized pairs look as well. You made a great choice with the Atriums. I remember loving what they did with vocals when demoed at Axpona 2024. I ordered the Tessideras on release and was able to pick them up at this year's Axpona (literally the only reason I wanted to go there). It was nice getting the chance to converse with Zach again. The stock canarywood looks so effortless, and I'm excited to enjoy music with them more. From my first session and especially compared to my long-running Caldera Opens, they do some really special things.

Do keep in mind I EQ all my headphones, but what I've heard seems to coincide with other folks who use the Tessideras stock. I've been using them with the thick pads and without the black mesh behind the pads/in front of the driver. The Tessidera's treble is wonderful, and it's one of those headphones that kind of goes against what you'd expect for the conventional hifi sound. The treble isn't in your face or loud and proud with sparkle/air, yet it still has great clarity and nuance. You don't lose out on tiny touches there. It reminds me a lot of Audeze treble, which follows largely the same trends. It seems like the new lattice structure is really doing its work, as I still perceive the Tess's treble as smoother than the Caldera Opens, even with both EQed.

To my complete surprise, I would say the Sennheiser HD 800 with EQ is quite a good vibing contender within my collection. Once you get rid of their treble-forward stock character (on my head) and fine-tune the bass/mids, they have pretty soft and rounded off transients that lend a slightly lush/full/relaxed quality to a lot of music. They don't sound especially "detailed," precise, or microscopic to me compared to most of my other headphones (even my EQed Aeon X Closed sounds a bit better in those areas), but the 800(S) still makes music very easy to enjoy when you want it to hang in the background. It helps that their comfort, especially with a Capra strap, is all-day levels of good.

I definitely heard the HD 800 as a bit lean/thin on my head stock, but it was more of a warm-bright character than anything. 6khz peaks on graphs always show up at 5khz for me, so instead of getting a stock sound that came off shrill, it was just accentuated. Alongside that, they also exhibit elevations in other parts of the treble that I also tend to EQ down with other headphones (mainly 8khz and 11-13khz). These seem to be related to features of my diffuse-field HRTF. These colorations gave off the impression of the HD 800 being cleaner and more incisive than it really was in a roughly HRTF-neutral state, and EQing it out led to that realization. Interestingly, the EQ profile for my Hedd D1s is quite similar from 5khz up, yet that headphone's sound remains clean and precise across music instead of becoming softer and more diffuse. In case it's a helpful visual, here are my profiles for the HD 800 and D1 respectively. https://preview.redd.it/d0i18dezfxqg1.png?width=1344&format=png&auto=webp&s=098d7fed7ed029283deabfcbda993e14819c3889 The HD 800's bass is still more rolled off than what I hear as neutral since the headphone doesn't get the best seal even without my thin-armed glasses on, but it's adequate enough to support that soft/relaxed character. Crossfeed is also being applied before these filters, both for preference and to assist with getting a sine sweep that sounds roughly flat in volume. When you turn off crossfeed, sine sweeps sound like what I imagine my diffuse-field HRTF is (a conclusion I was delighted to see confirmed by the Headphone Show crew). Besides the bass, there's still wiggle room for a bit of human error since I do everything above 1khz by ear and by referencing multiple squig measurements. Nonetheless, I think I've gotten precise enough over time to be really satisfied with my results across my collection.

I have a long string of thoughts in relation to yours, so here goes. No pressure to reply. I use a combination of Squig measurements, Owliophile/szynalski, and music to optimize each of my headphones. Crossfeed used is the Jan Meier option in Equalizer APO/Peace, and in RootlessJamesDSP, the BS2B Weak option seems to be the equivalent. I specifically aim for tilted diffuse-field neutral with all of them rather than explicitly aiming for different sounds. Nonetheless, they still all end up sounding different with their broad behaviors in areas like transient definition, separation/layering, and even core tonal characteristics. Those first two are quite important for my preferences and main genre of choice (high-energy EDM that tends to utilize the entire sonic spectrum and reveals a good bit about any one headphone's subjective capabilities). While some degree of human error is still in there, I've been a steadfast believer that headphone sound reproduction still has heavy reliance on a given headphone's design and what it's doing to get a given frequency response to your eardrums. On one side of the coin, while it's certainly cool to see that the Headphone Show folks got an HD 600 to sound near-identical to an 800S after on-head measurements and EQ, there's a big caveat I imagine is easy to ignore. There is a very real possibility that those results are a consequence of comparing two Sennheisers that probably borrow a lot of acoustic research and design cues. In the broad headphone world, this crew could have found an *exception* that happens to coincide with their long-standing assumption of the rule (that rule being "it's all FR at the eardrum and openness"). It's too limited and similar a comparison pool to confirm that kind of sweeping conclusion. Try one of those Sennheisers EQed to your diffuse-field HRTF against an Audeze, DCA, ZMF, Focal, or any other brand EQed the same way, and in my mind, the chances of subjective differences popping up that aren't exclusively FR-related would increase notably. They're inevitably going to sound quite close, but it's the subtleties where they begin to branch out. My experiences have told me that none of my headphones after fine-grain EQ sound 100% like one another 100% of the time, even after considering factors like session-to-session mood, pad compression and wear, or placement variation. Human error is one element, but said collection also encompasses a wide array of brands that almost never design their headphones exactly like one another. I'll go back to the D1s as an anchor. One thing that might make its sound consistently clean and separated/layered to my ears would have to do with [the extensive research Composite Sound (the company that helped Hedd with development) had to exercise](https://www.composite-sound.com/technology/#Second-Generation-TPCD) to optimize the behavior of that headphone's diaphragm (increased control over its stiffness and motion) compared to other dynamic-cone transducers. What's being done with that driver would not only assist with the final FR (the D1s show an especially linear and predictable treble slope outside of HRTF features), but would also fare positively for the above aspects because that diaphragm was engineered to behave in a highly controlled (and accurate) manner. Allow me to put things further into perspective and introduce a couple trends. My EQ experiences have also found on the planar side that planars designed with increased tension via tighter control over the diaphragm (primarily Audezes and ZMF planars) tend to sound consistently clearer/cleaner, more incisive/less soft, more dynamic, and less diffuse than planars with more loosely tensioned diaphragms (like Moondrops and HiFiMans). Back on the dynamic driver side, the D1s fall neatly into the former camp, and the HD 800 would fall neatly into the latter. My preferences index more heavily for the former, so there is even an element of strategy to finding headphones with those kinds of design philosophies, though it's not super clear-cut. These are trends (among other examples) that our audiophile and audio enthusiast bubble could very well be looking into for additional variables regarding why we perceive sound the way we do, yet they are simply not being investigated. We're conditioned to only care about the final frequency response because it's treated as this immutable variable that more or less dictates headphone sound. Effective EQ can optimize phase, but it can't fix non-pistonic diaphragm behavior, pad bounce, standing waves, or other design-related cancellations, nor can it change how a given design is directing sound to your ears (such as via pad shape and magnet structure in the case of planars). You can't EQ the design you're working with. Additionally, like you said, we don't have an easy way of seeing these potential behavior differences in real time, nor is ABX blind-testing different headphones feasible when the topic of interest is behavior for that headphone specifically. Transposing its frequency response into another headphone as a means of comparison misses the point entirely. At the very least, I hope this direction, one that integrates science from other fields to fill in our current gaps, is the direction our space heads towards.

Yea, minimum phase is still one of the big things keeping what I say a bit hazy and difficult to maneuver around. Even then, it's still good to recognize examples of headphones that actually are out of phase in at least one area of their FRs for one reason or another. There are three examples that come to mind for me, two in the bass and one in the upper treble. 1. [The excess group delay for the Fosi i5, as measured by unheardlab](https://unheardlab.com/wp-content/uploads/2025/08/fosi-audio-i5-excess-group-delay.png?w=1500&h=), shows very unusual behavior in the bass below 100hz. Minimum phase headphones ordinarily show [an exponential rise in their curves as they go towards 20hz](https://www.audiosciencereview.com/forum/index.php?attachments/dan-clark-e3-closed-back-headphone-group-delay-response-measurement-png.330972/), but the i5 appears to exhibit the exact opposite behavior. Its curve is plummeting instead. I'm not sure what sound consequences this would have, but it's certainly an anomaly I haven't seen anywhere else. It sounds like it can happen with subwoofer systems. 2. This second one isn't plotted as excess group delay, but it was replicated with RTings' measurements of the same headphone (just a shame they now prevent you from viewing said measurements by default). I recall them saying the 2021 version of the Audeze LCD-X was out of phase by one wavelength in the subbass, and this also showed up with [Amir's normal group delay measurement](https://www.audiosciencereview.com/forum/index.php?attachments/audeze-lcd-x-measurements-group-delay-vs-frequency-response-2021-png.143665/). This is another case where audible effects are unclear, [but if the LCD-2s in my stable are anything to go by](https://diyaudioheaven.wordpress.com/wp-content/uploads/2021/06/gd-lcd2f.png), there's a chance this delay in subbass phase leads to an elevated sensation of density and meatiness in bass transients. Just a guess though, and if this is true, it would tag alongside the plunger effect from the completely closed front volume. 3. This last one is for a headphone I'm more intimately familiar with than anything I've ever owned: the ZMF Caldera Opens. They exhibit standing waves in the upper treble frequencies. This manifests as a series of extremely high-Q peaks and nulls through the treble ([see here and how it compares to the upcoming Tessidera](https://www.head-fi.org/threads/tessidera-the-new-euphonic-planar-from-zmf.979639/page-4#post-19038220), which effectively eliminates those waves through an acoustic lattice/matrix that helps diffuse backwaves out the wood cups in the back). The Atrium Damping System (ADS) already tried to minimize this, so it was clear some extra tech needed to be integrated for full effect. I could actually hear nulls shifting around on my head in sine sweeps every once in a while, and other times they weren't there at all. This behavior is further confirmed by [highly unusual group delay in the same band](https://www.audiosciencereview.com/forum/index.php?attachments/zmf-caldera-planar-magnetic-headphone-group-delay-response-measurements-png.330537/) (with everything else below being minimum phase), [alongside resonances in the CSD that clearly contradict the clean decay with a measured peak before that region](https://superbestaudiofriends.org/index.php?attachments/upload_2022-11-28_12-18-20-png.34057/). In actual listening and after EQ, the effects of these standing wave cancellations seem surprisingly subtle, yet I'm certain they have still permeated the Caldera Open's behavior in both highly positive and slightly negative ways. My previous comment on diaphragm-related trends still apply here, yet the COs still have a slight tinge of diffuseness, a slight softness and lushness, and a slight reduction in overall dynamism (that last one in comparison to something like the Audeze LCD-4zs). I always thought the COs were unusually unforgiving of muddy recordings as well, so these cancellations might have exacerbated those flaws. Despite the alleged effects of this narrow range, the Calderas have remained my favorite headphone for a reason. It's an objective flaw that has probably added to the music more than it has harmed it. Regarding your thoughts on hearing ability, I have a hunch that every one of us in this space is capable of "hearing through the FR" to try and get a taste for what a headphone is trying to do on the design level. Brain burn-in seems to serve as a notable effort to do this exact thing, and the closer you get to HRTF-neutral via EQ, the quicker/easier it is to perceptually tune out human-error-related colorations and hear how a given headphone is really behaving on a fundamental level. That's at least how I think about this, as my previous comment also explored. I also believe that you and other people are probably hearing broad differences between headphones that aren't exclusively tied to the FR, but it's difficult to *perceive* and *acknowledge* those differences as long as notable FR colorations continue to cloud assessment. It's just about impossible for me to agree with the idea that EQing so many different headphones to your diffuse-field HRTF makes them so close to identical that consumer choice comes down to aspects like price, build, and comfort. That probably can happen with edge cases like the HD 600 and 800 series, maybe even if you go the binaural head tracking route, but the former might still end up a rarity. I guess those kinds of conclusions are what happens when my preferences have become agonizingly specific, while most people like you will be perfectly satisfied with something that just sounds pleasing. Keep up that enjoyment if you can, as it's important to realize how few people my experiences will actually apply to. I'll leave it there (it's too late for me too), but it was nice just synthesizing my thoughts with you. 🤝

I've held off on a post talking about my experience with the Calderas (the opens) for too long now. I have a lot to say for folks to fully understand why they're my favorite headphone, not just in the summit space. They're irreplaceable.

Hi Everyone! TL;DR: The ZMF Atrium Redwood Burl are works of art and sound incredible, super happy. I was on a mission to try out several headphones I've been unable to demo elsewhere and hopefully come away with an idea of what would be next for me. I've been spoiled for choice with some of the local shops here in the Twin Cities area but a few brands/higher-end options haven't been available. I reached out to ZMF to ask if they offer workshop tours and have demo units available to try. I thought I'd make a trip to Chicago and pay them a visit. While they do have kind of open-house days, they also told me they'd be at AXPONA. I'm a bit embarrassed to say I'd not heard of it prior, as I had only known of Canjam. I had previously lived in the LA area so the show was there all the time, but I had been pretty happy with my HD800S and LCD-X for a while, so I had not visited in years. I decided I'd visit AXPONA since pretty much everyone would be there and I'd be able to demo pretty much anything I'd be looking for. I made the rounds and tested several headphones out I had been considering and pretty much steered clear of the options that are $10k+ or of questionable quality/new brands. Any and everything was there to demo, but I didn't want try stuff that would linger in the back of my mind and ruin my wallet (Warwick) or disappear from existence in a few years. I tried the Audio Technica ADX3000 and ADX7000, ZMF Auteur Classics, Atrium, Tessidera, and Caldera. I also tried the Hifiman Arya Organic and Arya Unveiled despite being a Hifiman hater. I'd pretty much tried other contenders at the local shops; Meze Empyrean II and Elites, Audeze LCD5, Focal Utopia and Clear MGs, and Fostex TH1100RP. I like my HD800S, but I've since given them to my wife and I wanted kind of the "next level" for open backs and perhaps something with a bit more bass (thanks Sony) and "different" tuning. The ADX3000 and ADX7000 both had interesting tuning and I'd have loved to listen to them longer, but I didn't like any of the AT pads, the ear opening is just too small for my ears. The Hifimans I tried: The Arya Unveiled made me nervous to touch it ,and the booth had it hooked up to a laptop with literally only one Led Zeppelin song in windows media player. I didn't sit there long. The Arya Organic sounded pretty good, but I could not get them to feel secure on my head. Huge ear openings and relatively comfortable, but they kind of sloshed around on my head. Unfortunately for them, I had already visited the ZMF booth and the wood veneer and overall build quality just felt bad (I'd hazard to say not just bad by constrast, but just objectively bad). I also didn't listen to them for very long either as the track-list available at the Moon Audio booth was pretty poor and the folks working there were kind of cold / perhaps more interested in peddling cable snake oil to old folks with more money than sense. Sidebar: Shame on the audio industry and a lot of the trade show vendors for just making up lies about cables. I heard a vendor I won't name talking about $5000 speaker wire and $9000 1m long XLR cables. Onto the ZMF booth. Auteur Classics - like the HD600s but more of everything, including weight. I felt these would cause some discomfort for longer listening sessions and they didn't quite feel like "enough" of an upgrade to my ears from what I'm used to. I tried the new Tessidera and Caldera and both also felt too heavy for me despite the otherwise great ergonomics. I also think in contrast to the Atrium the timbre and the midrange of those planars just didn't hit right with me. I think they're both very technically competent with interesting tuning, but the key here is contrast. So the Atriums. Kind of funny, both my wife and I had the same general first impression, "wow". I sat with these the longest as it was clear to me these struck a lot of the right chords (pun intended). To sum them up in simplest terms, they have authority. Notes have heft/impact. The mids/upper mids are a bit forward, the bass hits hard, the treble is detailed, but not too bright. Instrument separation is good, sound stage isn't huge, but it's not overly intimate. Others have written more eloquently than me on how these sound, so I won't go on. I had a separate problem now, can I get one? The folks working the booth were great, especially Bevin, she was super helpful and very gracious. We went through the list of options they had available there and I felt like a kid in a candy store. There were so many wonderful combinations to choose from. The decision was complicated by some banter between Zeos, Bevin, and Zach. There was discussion of boneless versus bone-in chicken, chef boyardee resin stabilized LTDs, etc. I'm just standing there admiring the different wood, chassis, and grill choices. A truly surreal experience. Ultimately the Redwood Burls suited me best. Coming in at almost exactly 500 grams, they are hefty, but among the lighter options there because of their lower density. They have a really great sonic character and look stunning. The Atriums are a really special headphone that just ended up doing more right for me than everything else I've tried recently and I've been super happy listening to them the past few days. To those that made it all the way through, thanks for reading. If you have questions about why I chose these over some of the other models listed, I can answer in the comments, this post is already too long.

ZMF Caldera. Beautiful, comfortable, amazing sound.

Not if OP thinks this highly of the Caldera. I'm very much the opposite and the Expanse and Stealth are some of my absolute favorites while the Calderas (both open and closed) were underwhelming for me. Love my VCs and AOs though. Edit: The E3s were also very good.

My current endgame is Arya Unveiled. I tried a lot of cans and this was the best one for me. Next up, I might get HEKU or SUSU but not this year. Other option I really liked was ZMF Caldera and Focal Utopia. Until then I think Arya Unveiled will do nicely. P.S. I tried Audeze LCD-X, LCD-2C (open), LCD-2C (closed), LCD S20, LCD-3, LCD, 4z, LCD-5 and CBRN2. The two I really liked were LCD-2C open and Audeze Maxwell 2. I walked out with Audeze Maxwell 2 which sounded even better than CBRN2 to me. I know it might be a nub thing to say but I don’t have any popular opinions and in my experience after trying over 100 cans is that money doesn’t mean better sound to me. And most audiophile recommendations are not for me. YMMV.

Modhouse Tungsten DS or ZMF Caldera HD650 on a high end OTL