ZMF Caldera review - Forged in Fire

ZMF headphones is a company that makes high end hand crafted wooden headphones out of Chicago, Illinois. I always wished for a contemporary planar headphone offering from Zach the owner of ZMF as his previous planar offering were the modded fostex t50rp headphones. I never heard said headphone but assumed that a new planar offering from Zach built with his years of headphone making experience would create something truly special. I guess people should start calling me Nostradamus because that headphone now sits before me from the master forge deep in mount doom… the Caldera! Zach was nice enough to temporarily loan me a pair for review and was very clear that there were no strings attached with the review.

Build quality, Comfort, Setup
The Caldera has a gorgeous build quality that ZMF is now known for. The real wood cups feel very premium in the hands and the caldera / volcano grill pattern is beautiful. Please believe me when I say pictures do not do it justice. The tank-like pelican style case the Caldera comes in is much appreciated for shipping / storage protection. The included black mini XLR to 4 pin XLR cable feels well made. I found the Caldera like many ZMF headphones to be extremely comfortable. The thick microsuede cushions of the pads and generous suspension headband means I can listen to the Caldera for hours without fatigue. Please note I listened just on the vegan suede pads just because I prefer all synthetic materials in my headphones. Dacs used were Denafrips terminator OG and north star designs 192 dac.


I listened to the Caldera with a variety of amps including some speaker amps, namely the Bottlehead Crack, Audio gd he9, Pass labs x350.8, Conrad Johnson LP70S and Willsenton R800i. I was shocked to find the little Crack could drive the Caldera well and was a very enjoyable pairing… but the caldera DID scale with better amplification. I tended to prefer tubes with the Caldera which leaned into the naturally fluid and musical character of the headphone. The r800i was my favorite pairing which greatly bumped up Caldera's resolution, sound stage and dimensional layering.

Tone + Timbre
The ZMF Caldera is a tonally warm sounding headphone overall which lends it to sound somewhat relaxed and laid back but this is not at the expense of clarity, resolution and microdetail which is excellent. One of the tonal qualities that stands out to me is the balance between a silky, fluid sound while still retaining great technical performance. You could say a great balance between musicality and technicality but I think that wouldn’t do justice to the superb balance the caldera achieves.

Sound stage
Caldera is spacious sounding with a good amount of air between instruments. If HD800S is the benchmark for large space rendered acoustic spaces, the Caldera is about 80% as large in all dimensions. I never felt wanting for a bigger and more airy sound and indeed with orchestral music the Caldera renders the scale of the orchestra exceptionally well !

Full, well extended, punchy and very detailed. The bass was actually very enjoyable and for me a good bass foundation to the sound is incredibly important and the caldera delivers this in spades! I found the bass struck a good balance between a weighty and possibly overly bloomy bass and one that is so fast that it's not satisfying in its heft. Detail heads that crave max detail from low end will be happy.

Mids were quite even and provided a palpable texture to vocals that was addictive. There was a classic ZMF fluidity here in the midband that I come to expect from ZMF but that I have not heard in other planar headphones like the D8000 and Abyss 1266 TC. The susvara is perhaps the only planar I have heard with that mid range tonal magic and smoothness and it makes for an engrossing experience. Planar headphones often need help in this part of the frequency spectrum more than traditional dynamic headphones.

Relaxed well extended treble was rendered by Caldera with just the right touch of sparkle. Caldera is not going to produce as much brilliance as a brightly tuned headphone but I prefer this type of tuning which is easier to listen to for extended sessions. There is absolutely no fatigue but I did not feel the treble was dull.


Chloe Agne - Walking in the Air was a great track that showed off what Caldera treble could do… Throughout the track there are bells of many different types and they sound appropriately metallic. Chloe’s voice soared on the caldera and was very clear, present and fluid.

Moving to ‘The Prayer’ on the same album the delicacy of the solo violin was rendered with wonderfully accurate timbre and tone and was rendered in its own space that allowed the listener to focus and track it as it danced with Chloe’s powerful voice. As the whole supporting symphony comes in I am struck by the well portrayed sense of grandeur the Caldera affords.

Houston Person - Never let me go (Rain or Shine) was a truly mesmerizing track on the Caldera. Houston’s saxophone playing came across with just enough of the smokey jazz bar swagger I look for in pieces like this but with a remarkable amount of crispness and focus that I often lose on headphones or chains that specialize in tonal beauty. The ‘blareyness and brassiness’ of the sax is well portrayed especially when Houston hits a crescendo. The piano strikes are crisp and distinct while sounding accurate. Cymbal taps by the drummer were so shockingly realistic it was as if I was sitting right next to him and I could touch him. The double bass was present but very very clean sounding where it can sometimes sound a bit too heavy handed and emphasized.

Vivaldi - Concerto for Lute, 2 violins and Continuo in D Major, RV93:3 Allegro (Vivaldi Winter vibes) highlights the strength of the previously discussed balance the Caldera has achieved. The lute strings have just the right amount of snap but there is a woodiness to the timbre that allows you to musically engage in a deeper way. Almost as if you have a slight burnishing of the plucks that bring out their beauty. VIolin sounds both delicate in the decrescendos but powerful and intense in the crescendo. I was struck by the Caldera’s ability to deliver a natural tonal presentation. Classical music lovers will rejoice as Caldera does justice to the technical aspect but also the romantic aspect of many classical pieces.

Steffi - Nightspacer (Yours and Mine) is an intense techno song that allowed Caldera to demonstrate its deep bass prowess. Bass had excellent dynamic slam and was in the same domain as my current reference bass king the Atticus but was more detailed and extended. The track is quite layered in its approach to introducing new synthetic sounds and this was all rendered with a precision, speed and a focus that made it clear the Caldera is a techno beast. Treble was well extended with fast transients that this track demands yet was nice in that it didn’t assault ears with ice picks as many other headphones/chains can do.

Vs the HD800S there was really no comparison here. I think I would almost always reach for the Caldera over the 800S. It just was richer, more saturated and more satisfying then the thinner more nasal 800S. Don’t get me wrong 800S can sound very good on the right chain but across the board the added dose of thickness in the mids and bass was something I simply prefer.

Vs the ETA O2 headphone this was an interesting comparison. The O2 is a lot cheaper but shockingly performs extremely well. I think tonally the O2 is brighter and sometimes that added touch of brightness is appreciated for the brilliance it delivers like in the aforementioned Chloe Agnew track. Caldera may be slightly more resolving but it was fairly close.

Vs ZMF Atticus. The Atticus is probably my favorite headphone I own. It is the DEFINITION of a musical sound. Warm, rich, inviting with mids that reach out and kiss you write on the lips. Sorry going a bit too far there the point is its a beautiful sound. Generous, heavy with extremely full bass. Is it for a detail / transparency head? No. Is it for someone who listens to music for the emotional impact and ‘soul’ that can at times be evoked with the right chain? Yes.

After that big build up how does Caldera compare? Caldera is more detailed, more airy, more extended up top and I can see it being a great companion headphone. Caldera sounds bigger with more space between instruments and singers. Atticus is more intimate but in a very satisfying way. Tonally Atticus is FAR WARMER than Caldera which sounds downright neutral in comparison. I’d recommend owning both if you can… when you're in the mood… and you’ll know when it's time, reach for atticus… when you feel somewhat ‘normal’ Caldera is probably what you’ll reach for.

Vs HD650… this comparison goes very similar to the one with Atticus except I find the Atticus is just a better headphone in basically every domain.

Price is obviously something to consider as the Caldera is $2500+ depending on which version you get. Although I would have loved a $1500 headphone with similar performance I think its probably not that realistic. When you factor in the excellent performance and superb build quality I can understand Zach setting the price where he did.

If you are a ZMF head who craves max musicality the Caldera may come across a touch ‘too neutral’ and buttoned up. I think its still absolutely worth trying though even if you have to buy and resell because you may like Zach’s vision on this headphone .

If you made it this far I think it goes without saying that Zach has delivered an excellent although quite different sounding headphone than he tends to produce. I think there are many people who are on both sides of the spectrum between technical speed, clarity and resolution and soulful musical bloom that will meet at the intersection the Caldera has brought to the fore. Caldera is an exceptional headphone and performs well in all genres of music that I have heard on it. It is with great pleasure that I strongly recommend it! I am happy to award it the Sonic Visionary award!

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