ZMF Atrium Closed Impressions, Analysis, and Measurement

Zach generously loaned me a demo pair of the upcoming Atrium-Closed (hereafter also referred to as AC) for my review. Like I did with the Caldera, I will periodically update this thread with both subjective and objective observations/analysis.

The demo pair I received is made of Olive wood (LTD wood at launch to my knowledge). I have no idea about the price. But judging from the Verite Closed case, I believe that the regular price will be very similar to that of Atrium Open (AO).

The demo headphones came with two different sets of pads: Caldera Lamb and Caldera Suede. The lamb pads were visibly thinner than the stock perforated lamb pads of Caldera. Likely Caldera Lamb-Thin. I also confirmed the demo unit had much wider headstrap than previous ZMF products (up to Caldera), which is a very nice plus in ergonomics.

As always with ZMF products, my views/thoughts may be quite biased, no matter how hard I try to remain fair and transparent. This demo pair was also made very recently and just arrived at my place a couple of days ago. So, it may take a while for the drivers to be fully stable (my brain/ears need to adjust to AC as well). Please be ready for some bias in both directions.

Anyway, AC’s sound was very interesting and promising. Here are some very first impressions I made today and yesterday after listening for 10+ hours.

• AC and AO are quite different in tonality. VC-VO is far much closer to my ears than AC-AO.
• AC almost seems on par with AO or VC in technical performance but I want to spend more before making any bold claims.
• AC has ZMF-Biodyna coloration like AO, Auteur, Ekon. Very similar pattern in harmonic excitation (in mids).
• Although a little hot in the treble, overall very balanced V-shaped tonal balance that I find experientially neutral-ish (perhaps the most so.. but I digress for now). Fantastic extensions on both ends.
• The closest ZMF I can think of is Eikon. A very very uber high-end retake though.
• Lamb (thin) pads are much preferable than suede. Suede pads make the AC regain mid-centricity, which didn’t seem to go well with my current taste.

I’m planning to collect more thoughts and take measurements in the next few weeks. In the meantime, any questions or other first-hand impressions are welcome.

PS. The unit I received weighed 520g without the cable.

 

Day 7 Impression

It’s been one week with the Atrium-Closed (AC). I think I have a slightly better understanding of what these headphones are trying to do than I did at first. Perhaps a good timing to organize thoughts that I collected so far, before exploring AC sound even further..

This may be a minor point, but I noticed that the headband was flexed more than some previous ZMF units (including the demo Caldera) -- this was also noticed on the Auteur Classic SBAF loaner unit. And because of the increased flex, the clamping got tighter. This is definitely a welcome change. As I complained slightly in the Caldera review, the ZMF swivel structure often creates loose/broken seals at the bottom of the earpads, which can sometimes result in a slight loss in the sub-bass. I found that the AC demo unit pushed the ear pads more evenly and firmly. Needless to say, this helps to pull everything out of the low-frequency potentials. I suspect that this clamping change is not product-specific, but rather the result of newer manufacturing processes that benefit the entire ZMF lineup. Or maybe I was just unlucky before. IDK.

As I discussed in the Caldera and Athena analyses, I have found that I do not hear lows below 400Hz or highs above 4kHz any louder than the mid-frequency range, which makes me prefer audio tools that are tuned to my loudness perception. Simply put, now I have a strong preference for V-shaped tonal balance (which sounds more neutral to my ears) and an aversion to mid-centric sounding devices (which sound lacking in both treble and bass). While it’s not yet clear what the right amount of V-ness is, the AC sounded relatively more neutral to me than many measurably-neutral headphones. The low-to-mid-to-high ratio is in line with the spectral balance, which I find to be experientially neutral in the grand scheme of things.

In many tracks that I listen to frequently, harmonics in the mid to upper midrange play a dominant role in attracting and holding my focus. The clarity and presence of many core instruments that lead melodies (e.g., vocals, electric guitar) are strongly affected by harmonics between 2-3kHz. The main problem I have with mid-centric speakers or headphones is that the impact of this frequency range is too dominant. The more my ears are focused on the midrange, the less rich details they can pick up in the low or high frequencies (e.g., vocal fundamentals/body and air respectively). Also, I always find a little better overall balance in the soundstage when vocals/guitars are pushed back a bit. When tracks are dense and filled with a lot of complicated signals, the benefit of neutral perceived loudness is even bigger for me.

I also noticed some lovely colorations in the midrange. This seems to happen in two ways. First, vocals are emphasized a bit more (without breaking the V-balance) than what I consider loudness-neutral. I wonder if the energy level of the upper midrange is slightly increased. Second, there’s also a hint of harmonic coloration in the midrange that I almost always hear in many ZMF biocellulose-dynamic drivers. There are some subtle additions to the human voice that feel a little thin, but sweet. These two effects, along with the great tonal balance, make many vocal recordings sound very addictive. The balance among opposing elements is impressive.

I’ll keep listening and update the subjectives if anything interesting comes up.

 

Zach uploaded a video explaining the details of the Atrium damping system (for the first time to my knowledge) and some of his measurements with and without the damping system. These are neither my analysis nor my own measurements. But I thought it might be helpful to have it next to my impression/analysis/review.

Here are some screenshots from the video for those who don't' want to pay full attention to the 7-min video.




I guess that the two diagrams above probably came from the patent document. Interesting to see ADS is visibly differently configured in the open-back and closed-back headphones. Zach explained that ADS in the closed-back enclosure helped to diffuse sound radiation on the back so that the overall reproduction is more like that in the open-back headphones. During the short video, I couldn't learn all the details, which may require full-hour or multi-hour lectures. But I'm sorta customer to be pleased when many interesting-ish thoughts put in the product. Haha.

Later in the video, Zach demonstrated the incremental effect of ADS in a couple of measurements. These are very interesting because this kind of controlled comparison is usually impossible to be conducted on the consumer side.



The top and bottom graphs are impulse response and frequency response plots respectively. My guess is that this measurement was taken with his B&K 5128 and FR was compensated for the diffuse-field equalization (Zach didn't specify in the video).

Thicker lines (solid thick line on the top plot and dashed thick line on the bottom plot; legended by CH3) are results from the Atrium-Closed (AC) without ADS, while thinner lines are from with ADS.

With ADS, the impulse response shows more mitigated overshoots and faster recovery from the stimulus are seen in the impulse response. In the FR, ADS contributed to a more consistent bass response and smoother upper mids. The effect on the lower mids and treble regions isn't as clear to my eyes.

I will also take my own measurements when I have time. Tbh I'm postponing this on purpose because postponing measurements is usually helpful for me to focus better without fear of confirmation bias.

Below is the video I talked about in this post.

 

If you get some time to think about the AC-Eikon comparison, that'd be interesting to read. I don't know that I need/want a closed headphone to be better than the Eikon (it's not perfect to me, but very very good, and I suspect a lot of the limitations are closed headphone limitations), but I've seen that thought pop up a few places, so I'm curious as to what exactly is like and unlike there.

 

Apologies for the delayed update, but after extensive time spent with Atrium Closed, I can confidently reaffirm my earlier bold claims about its impressive performance. In my opinion, it is the second-best headphone Zach has ever built, standing as the best-sounding ZMF electro-dynamic headphone. Let me delve into how Atrium-C excels in tonality and technicality. I'll do my best to remain unbiased and impartial. But be aware of any bias my impression may have.

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Tonal Balance

ZMF headphones have always fared well in the bass department. Atrium-C offers a perfect balance of bass energy and low-end extension. Below 500Hz, bass energy levels are a few decibels higher, gradually increasing by about +2~3db/octave, aligning with my hearing loss in the bass region. It extends down to 20Hz without attenuation. Atrium-C's unique flavor is deep, delicate, and non-congested, though not exceptionally hard-hitting – a stark contrast to Atrium Open's performance.

Some might consider midrange a love-or-hate aspect; I find it well-balanced, particularly with Caldera lamb pads. A slight recession in the mids accentuates lows and highs - appropriate for my older ears.

Atrium-C's treble is reminiscent of Verite and Eikon, blending each strength skillfully. Upper midrange nuances gradually increase, and treble leans towards the aggressive end. Some recordings may appear harsh or sibilant to specific listeners, but I haven't encountered any sibilance issues.



Linda Lindas' Growing Up (2022) showcases Atrium-C's prowess in reproducing each musical component. The fundamentals of female vocals are solid, and kick drums pack a punch. Bass guitar carries appropriate weight without sacrificing richness or power. Snare drums exhibit a softer bark, and Atrium-C renders laid-back, cuppy but not nasal vocals. Interestingly, despite some shortcomings if any, the headphones manage to deliver an engaging listening experience.


Technical Performance

Atrium-C has a more colored timbre compared to Atrium Open, which leans towards realistic and life-like. Atrium-C offers smooth coloration, slightly elongated note decay, and a generally non-aggressive presentation, suiting the delicate nature of its reproduction. While I enjoy this, it may not suit everyone's taste.

Soundstage is highly impressive, with only a little hints of boxiness or cup reverbs. Though slightly narrower and less deep than Caldera, Atrium-C provides one of the best soundstage experiences from closed-back headphones across varied price points. In fact, its spatiality compares well with open-back electrodynamic headphones like Verite.

Atrium-C's dynamics may be its weakest aspect. While it resolves nuance and volume gradation well, macro performance may feel congested. During climax passages of orchestral scores, the headphones' reproduction is loud but slightly compressed.



Listening to Stravinsky Ballets performed by Sir Simon Rattle and LSO highlights Atrium-C's strengths and weaknesses. It may not be as powerful as Caldera, but it offers a soulful and convincing rendition. The subtlety of lower strings is easily discernible, but orchestration may lack some clarity. Transitions to full orchestration are less impactful than desired, with limited heft and weight.



Similarly, while listening to Oster Peterson Meets Roy Hargrove And Ralph Moore, Atrium-C demonstrates its strengths and weaknesses. I think I can capture the equivalently good picture of the whole musical structure and developments I heard with Caldera. I may nitpick that the piano is sometimes sacrificed as I attend to the cymbal accent more. However, the balance between spicy cymbal and rich piano remains top-notch, ensuring an enjoyable listening experience.

 

Measurements

Notes on method

• All the results below were taken with MiniDSP EARS.
• The frequency response has been compensated for a home-brew hybrid curve that is derived from several different profiles.
• The "ideal response" curve is overlaid with the product FR as a subjective neutral reference.
  • This response is derived from a weighted log-level average from several different products that I believe are tonally well-balanced in their own right: ZMF Caldera, DCA Stealth, HarmonicDyne Athena, HFM Susvara.
  • In this curve, multiple considerations (hearing loss, my usual listening level, equal loudness) have been factored in.
  • Please take the "ideal response" curve with a grain of salt due to its highly experimental nature (at least for now).

Highlights

• The overall frequency response is close to what I perceive/believe to be neutral in my usual listening volume.
• The low frequency extension is great, easily extending down to 10 Hz. This is not often seen in electrodynamic headphones.
• There is a subtle wonkiness in the bass response, which is probably due to cancellations among internal reflections.
• The C-suede (Caldera suede) pads lift the midrange levels at a cost of a much hotter upper midrange. This did not work for me, but it may be good for some people.
• The upper midrange is a little hot, and this is easily audible (in not necessarily bad ways). The seemingly strong peak at 8 kHz does not sound as bad as it may look. See my subjective impressions for more details.
• Within the ZMF spectrum, the Atrium-C is much closer to the Caldera than the Atrium Open.
• The resemblance to the Athena is interesting. The main difference between the two responses is in the upper midrange and brilliance, which is also pretty consistent with my subjective impressions.

 

Comparisons to other ZMFs

 

... and a couple of worthy comparisons.

 

I feel like this thread has been criminally neglected, so I’m here to kick-start it again. I set out to find a great complementary headphone to my Meze Elite. In the end, I decided a ZMF dynamic closed-back was the perfect contrast to my open-back planar. When the Atrium Closed became available in Ash wood, my favorite wood Zach uses, I knew resistance was futile.

I was not disappointed when these beauties arrived. At my request, Zach was gracious enough to select a set of cups that matched my OG Ash Auteurs that I’m so fond of. They look amazing, and look like the long-lost brother of my Auteur. I couldn’t be more pleased with them aesthetically. Here are a few close-ups of the AC and then one of them next to my Auteur.

I only have a few hours listening time with these so far, but they have impressed me. The bass specifically really packs a punch and goes very deep. It’s a more visceral bass than what I get from my Elite. If anything, the bass, at least initially, is a bit fatiguing after an hour or so. I need to acclimate to it and also let the headphones burn in a bit.

As many of you already know, pads can make a significant sonic difference on ZMFs, so I bought 3 different pads to go along with the stock Caldera Lambskin Thins. I’ve got Caldera Suede, Bokeh Suede, and Auteur Suede (solid) to eventually try out, though I’m going to stick with the stock pads for the first week or two before doing any pad rolling.

I’ve mostly been using the Yggdrasil A2/MJ3 combo and it seems to be an excellent pairing so far. On the MJ3, I’m using XLR in/out, low gain, single-ended Class A, and no feedback. “Smooth” and “rich” are what come to mind. It’s a very pleasant sound.

I also have my SW51+ connected to the RCA output of the Yggdrasil, so I tried the AC on that last night as well. I used the high-Z output, and I liked what I heard. The somewhat neutral SW51+ made for a good matchup with the bassy AC. I’ll have to do some more careful comparisons in the future, but the SW51+ was not definitively outclassed by the MJ3 when using the AC, so synergy seems to be strong here. With my Elite, the MJ3 is a noticeable step-up from the SW51+ or my Cayin iHA-6.

I’ll report back in more detail on my sound impressions once I’ve had more time with the headphones. At least initially, I love the look and the sound of these things. Zach was so helpful throughout and really does go above and beyond for his customers! I hope more people here get a chance to try these out. The bass is quite the experience, in the classiest way possible of course.

 

Any chance we could get a loaner? There is so much info (praise) out there about the AO and VC. The lack of buzz for the AC seems unfair.

 

One small note is that this unit is an olive wood set - a harder wood, with snapper bass and resolve, the softer woods like cherry, redwood, Koa etc will have more of that "space" but less immediate resolve. Such is the trade off with closed headphones made out of woods with different densities.
Thanks for the write up @ChaChaRealSmooth I'll get those extra pads over shortly so we can start the tour!

 

On top of awesome (as usual) and spot-on impression from @ChaChaRealSmooth , I'd like to offer my perspective on the sound staging abilities of the Atrium Closed (AC) headphones compared to the Verite Closed (VC). Based on my listening experiments [1] , I found the AC to have a more accurate and conservative representation of recording venue boundaries, while the VC seems to exaggerate the sense of space, making things sound more open and distant.

For context, I believe the VC, AC, and Stealth (DCA) are the top 3 (spatially) best sounding closed-back headphones I've ever tried. My relative take on each is that the Stealth reproduces space precisely but with somewhat dry reverberation. The VC creates a pleasingly boundless/lively soundstage that can fool me into thinking I'm listening to open-back headphones. The AC falls somewhere in between, perhaps a bit closer to the Stealth. Of course, all these are just from my observation and there may be more confounding factors that I don't realize (e.g., wood material like @zach915m mentioned).

Which sound staging is best comes down to genre, recording quality, and personal preference. There likely won't be universal consensus.

Footnotes
[1] I did small experiments to listen to my own recording that I clearly knew how large/open it should sound by nature.

 

I’ve spent some more time with my AC and have tried all the different pads with them at this point. I only used the stock Lambskin Caldera Thins for the first week to get a solid baseline for my pad comparisons.

The first alternative pads I tried were the Caldera Suedes. These are the standard recommendation from Zach as the secondary option alongside the stock pads. They are a bit thicker than the stock pads and gave my big ears a little more space, which was a welcome change. As far as sound, I felt they scaled back the bass quite substantially. In my opinion, they went further in that direction than I liked and made the AC a more balanced listen, which for me meant a less fun listen. At least for now with my current gear and preferences, I’ve decided these aren’t the best pad option for my use case because I want a noticeable contrast to my relatively balanced Meze Elite with Angled Alcantara pads.

Next up was the Bokeh Suedes. Zach recommended these to me as a good middle ground between the stock Caldera Thins and the Caldera Suedes. He was spot on in his description as usual. The Bokeh Suedes dial the bass back a small amount from the stock pads and make for a slightly more relaxing listen. They do manage to keep the “fun factor” intact though. I will say that these were extremely difficult to get on the AC. I had to manhandle them quite a bit to get them to fit. After I got them on the first time I didn’t have much trouble on my subsequent attempts. These were my favorite pads for a couple days, but something changed my mind which I’ll go into more detail about below.

The last pads I tried were the Auteur Suede Solids. These offer more isolation than all the perforated pads, but in turn sound more closed-in, like a typical closed-back headphone. The bass is still a strong presence with these, pretty close to the level of the stock pads. They were the most comfortable pads I tried because they were the softest and gave my ears the most room. Unfortunately, I value the open-sounding quality of the perforated pads more than the increased isolation and comfort these pads provide.

I had pretty much settled on the Bokeh Suedes as my pad of choice, then something happened that changed my mind. I happened to read the impressions of another AC owner where he said he started out with the stock Lambskin pads, switched to Suedes for a while, and in the end came back to stock pads again and found them perfect for him. He said this has happened to him on multiple ZMF headphones over the years. He said he always strays from the stock pads initially and then comes back to them eventually.

His experience prompted me to try the stock pads one more time. Turns out the headphones had burned in to the point of having the ideal amount of bass for me. It could be brain burn-in, but it seems many Atrium and Atrium Closed owners have experienced this rollercoaster of changes during the first 100 or so hours of use.

The moral of the story is to be sure to try all the different pads again after the headphones are fully burned in (100+ hours). I’m back to stock pads now and am enjoying the headphones a lot!

A few artsy-fartsy pics I snapped with portrait mode on my phone:

 

wow... I love my Cherry Eikon's, can't wait to get ears on these