Sound Impressions
Summary
The ZMF Headphones Caldera is a ‘massive-sounding’ planar headphone. However, unlike the Susvara, for example, it performs more to the emotive side as opposed to a focus on intense speed.
This is a headphone that simply ‘delivers’ with modern rock and pop, teasing out a driving rhythm and a strong physical presence with wonderful texture when called upon.
It has power, unbelievable depth, sub-bass presence, and a general timbral coloration that is more neutral than the Atrium but still relatively smooth and wonderfully easy to listen to in its own right.
Instrumental separation is spot on, with imaging spread out wide and deep creating an almost concert hall-type experience. It is not quite as ‘swirling’ as the Atrium equivalent but the transient response feels improved upon with spatial cues darting in and out at a quicker pace.
Vocals also have an excellent presence and focus, more so than the Atrium when compared side by side. I suspect the Caldera has a little more contrast also from a high-end that extends very nicely, surprisingly so for your typical ZMF tuning.
A little uptick in the upper treble helps bring a little bit of sparkle to higher-pitching vocal and percussion performances but not enough to tease out any undue sibilance.
Amping is super easy with the Caldera also. It is not too tough to drive but its potential explodes with a quality amplifier, nevertheless. It has enough transparency also to reflect the best attributes of whatever you plug it into.
For me, the Feliks Audio Envy produced exactly what I wanted from the Caldera in terms of power and imaging solidity. The only amp that came up a bit short for me was the shallower-staging TT2 but that is more of a personal preference thing than a poor performance in its own right.
Frequency Response
There are some aspects of the Harman Target Response curve that ZMF agrees to and you can pick that up in the Caldera tuning, most notably a narrow but noticeable lift around 2-3k that stretches the stage quite nicely, (front to back), and keeps vocals front and center.
However, the Caldera does not slavishly follow the curve to the letter with the 4-6k region dampened down which I suspect is in direct response to an upper treble peak around 8k that gives it that distinctive treble extension and sparkle not found on the Atrium.
Damping like that causes higher-pitched vocals to sound very rich and dense with just a hint of sweetness, rather than allowing sharp treble overtones or percussion splashiness to come through.
It’s the Caldera bass to mids tuning that is so impressive. It is incredibly linear and perfectly extended right down to 20Hz with virtually nothing in the way of attenuation to rob it of presence and power. The Atrium extended well with a nice punch but nothing like this, it is an almost tactile experience with the amount of air shifting when called upon.
Any drop into the lower mids around 300-400Hz is minuscule, with nothing scooped out and nothing to thin out the instrumental presence or push supporting instruments to the background. They sound bold, dense, and powerful as a result.
Timbre
It’s all about the timbre and a colossal fundamental, hence why I called this an emotive tuning, and it is not a ZMF headphone I guess without some nod to a very likable almost charming harmonic balance that is more even in bias than odd.
Now, as you will note in the pad impressions below, the stock pads are perhaps more neutral than the alternatives but even when stacked against the composition, the Caldera is going to sound relatively forgiving.
As a ZMF headphone though I have to say it is one of the cleaner-sounding sound signatures but without a hint of any troublesome planar treble steeliness.
There is a very subtle treble sheen that tightens up the note definition and creates a slightly drier presentation. There is also a bit more contrast in the timbre compared to the Atrium, with note decay a bit shorter.
I think that tweaks help a lot with the overall clarity but if you are looking for high levels of liquid-smooth edging to instrumental and vocal notes the Caldera will not go that far. There is a sensibility to its sound signature, and perhaps a developing maturity to go along with it. Forgiving? Yes. Overly soft or dreamy-like? No.
The fundamentals on the Caldera low-end notes are very satisfying, perhaps the most satisfying I have heard on a headphone this year.
It’s not a bloomy tone either, rather it is very planted sounding with excellent bottom weight on notes right up to the lower mids. It is not a sludge fest either, the layering and definition are excellent.
Staging & Dynamics
In a nutshell, the Caldera has unbelievably good depth, stellar width, and surprisingly good treble extension. Perhaps not as extreme in its atmospherics as the Atrium it more than compensates by producing some of the best planar sub-bass I have heard in a long time.
I think as few have mentioned how dynamic the Caldera bass can sound and there is some truth in that in the way it can flex and shift some air but at the same time, the linear tuning and purity of the response is still pure planar for me.
The lower mids are not pushed to the background either. The Caldera keeps them pulsing with a presence throughout topped only by that 2-3k jump for vocal clarity that helps keep that very strong 3-dimensionality to its presentation.
Vocals are forward but not as in your face as you might think. The Caldera does extremely well with space, spreading everything out and allowing them to image well without being suffocated by any energetic bass passages. A deft treble uplift around the 8k marker helps tease out that necessary sparkle and perceived height also without sounding sharp or unbalanced.
One thing to note, as with the Atrium testing, the Caldera staging emphasis can shift a little depending on your amp and source.
Amps like the Cayin HA-300MK2 will give you that classic ZMF emphasis on staging width and complexity just slightly less depth than I would like.
The Chord TT2 will shift it a bit more to excellent width and height. I wanted power and energy, however, and amps like the Feliks Audio Envy and the Ferrum OOR deliver plenty of both.
Synergy
Pad Swapping
The changes with the pads to the Caldera tuning are easy to pick up on. With the Cowhide version, the inner wall is much shorter which has the effect of bringing your ear a bit closer to the driver at the expense of a little bit of comfort compared to the stock pads.
It also has the effect of pulling the music closer so the overall presentation is somewhat more intimate in imaging, drawing you right in and giving you a more immersive experience.
The mid-bass and treble around 6-8k do seem a bit more emphasized which in turn heightens the contrast delivering a more vivid sounding but slightly leaner timbre but one that might prove to be more fatiguing in the long run compared to the stock pads.
Vocals also lose just a little bit of space around them and might just have lost a dB or two in presence by default.
The suede pads are supremely comfortable on the other hand, perhaps the most comfortable of the three. They pull your ears back a bit more from the driver compared to the cowhide pads to around the same level as the stock pad.
That being said it is probably the airiest of the three pads and the one that gives you the most tranquil delivery with a slight attenuation of the sub-bass performance sub-30-4Hz and 1-2dB from the lower-mids presence to go along with it.
The perceived enhanced headroom is more from a lift in the treble at around 5k again accentuating that 8k peak a bit more. It gives it a bit more sparkle and presence so the performance can range from sweet to slightly bright in the mids and highs, at least compared to the other two pads.
Efficiency
The Caldera is rated at a slightly high 60Ω with a rated SPL of 95dB. You won’t need massive power to drive it but a decent amplifier with good voltage and current headroom will allow them to run to its maximum potential.
Overall, it is not quite as demanding as the DCA EXPANSE or the Diana TC using something like the Feliks Audio Envy. You are talking roughly an 11 am volume dial setting versus 1-2 pm as a comparison with the competing pairs not that sensitive to micro-volume adjustments.
However, it is a step below class leaders in efficiency such as the 32Ω and 100dB SPL Meze Elite and the 14Ω Audeze LCD-5.
Tube Amplifier Pairings
Much like the Atrium testing process, I started with two tube amplifiers, the Feliks Audio Envy and the Cayin HA-300MK2. Ideally, both have enough flexibility to deliver high voltage and good current headroom to drive the Caldera quite well. These in turn were both connected to a Holo Audio Spring 2 DAC pulling FLAC files from the PC.
What I wanted to find out here was how well their respective power settings coped and the general synergy of each amp with the Caldera.
In the Atrium review, I felt the HA-300MK2 was the ideal pairing, given its expansive smooth and creamy stock tuning. However, in this instance, it was a switch around with the Envy providing the most satisfying performance.
Power Settings
On the Cayin, the 60Ω rating of the Caldera should slot right into the lowest setting from the 3-stage impedance system which cuts off 64Ω. Tonally, the Caldera sounds more ‘correct’ with a vocal image that’s slightly north of neutral but none too shouty.
That being said, I didn’t find any noticeable distortion from the performance in the middle setting or up to 250Ω. It does bring out a bit more aggression in the midrange, particularly the vocal performance, which has some additional sparkle and presence that I quite enjoyed.
It sounds even more exciting on the high impedance 600Ω marker but it might sound too vivid for some with vocals even more dominant. I enjoyed it for short blasts and ‘party music’ but for longer more studied listening sessions I would opt more for the medium or low settings.
Tonal Synergy
If you want depth as well as maximize the sub-bass density and speed of the Caldera then the Envy is going to give you the best performance. That solid-state rectifier keeps the bass tight and taught and very powerful sounding.
The HA-300MK2 is no slouch either but it sounds quite full on the lows, however, there is a little bit of attenuation sub-50Hz on the Caldera as well a softening of the leading edges which just dulls the comparative impact.
What the HA-300MK2 does really well maximizes the staging width giving the Caldera a huge X-axis performance. The timbre is smoother and creamier than the Envy pairing also with not quite as much contrast or treble sparkle providing a very euphonic overtone and one that old-school ZMF Headphones fans might prefer.
However, I think the ‘essence’ of the Caldera is better captured by the Envy which provides a more neutral timbre, stronger fundamentals, and a more precise and perceptively faster response.
There is less ‘swirl’ and atmosphere in the staging of the Envy pairing and like the Atrium it is all about the central image or spine of the performance. You could argue the staging is narrower as a result but it just feels more accurate with a more powerful delivery.
This is personal preference; I see arguments for both amplifiers depending on how you like your tone and staging quality.
Solid-State Pairings
For this process, I went with two of my preferred solid-state setups, the Ferrum OOR with its HYPSOS PSU and the Chord Electronics Hugo TT2 with the Hugo M Scaler upsampler connected.
Note, the TT2 is single-ended only so the default impression is SE for both amps with an annotation on the additional balanced performance of the OOR. For the supporting DAC into the OOR, I used a balanced line-out from the LP P6 Pro.
Power Settings
I actually found the TT2 to really a high volume to drive the Caldera satisfactorily, even in its high gain setting. I was hitting around -10dB on the TT2 with the M Scaler putting its maximum sampling rate before it got too loud.
With the OOR/HYPSOS using a line in the dial barely hit 11 am before getting too loud. Both setups had an excellent dynamic range so there isn’t a lack of voltage and decent current capacity.
On paper, the OOR is the more powerful of the two amps with a power curve that is strongest at 8W into 60Ω balanced which is just perfect for the Caldera. Subjectively or based on comparing the two performances the OOR does seem to provide more headroom for the Caldera, especially if you switch to its balanced mode.
Tonal Synergy
I honestly felt the TT2 took something away from the magic of the Caldera performance with the OOR/P6 Pro performance really nailing what this headphone is all about.
No doubt the TT2 is staging wider and taller than the OOR but it lacks depth with a very polite low-end response. On a lot of pairings, this is ok. The wall of detail from the TT2 more than compensates and yes you do get that detail here also.
However, for me, the Caldera needs that depth and power to sound correct and to sound complete over a wider range of genres, particularly modern rock and pop.
The TT2 is more anemic sounding with your ear being pulled up towards the mids, higher pitching vocals, and some treble also. A good match for acoustics, delicate high-fidelity, and any music that demands a wide stereo field.
The OOR, combined with the P6 Pro R2R balanced line out sounds more robust and heavier on the low-end, and that’s going SE, never mind balanced. It is not quite as expansive as the TT2 nor would I say this combo is quite as articulate or hyper-detailed.
What it does give you is a more natural sounding and denser tone with excellent depth and power. Key points that the Caldera much prefers and a performance that is much more emotive and easier on the ear.
Switching to balanced om the OOR will up the dynamic range and increase the level of instrumental separation which is a better pairing for me. However, even in SE, the tonal balance flows perfectly with the Caldera.
