My Olivewood AC aren't completely broken-in, yet, but now that I've spent more time with them I can hear their evolution.
These are my generalizations between the Z1R and AC:
1. Bass and Sub-bass:
The Z1R has an impressively dynamic and powerful bass that leans toward the mid-bass. It has good sub-bass presence, but not quite as pronounced as in the AC. The Atrium Closed, especially with the Caldera Thin pads, has a standout sub-bass and lower bass performance that can even rival planar headphones, which typically excel in these areas. The bass and sub-bass in the AC feel more elevated compared to the Z1R.
The AC has some of the most enjoyable bass I've ever heard; I prefer it over the LCD-5 and ZMF Caldera. I believe this is due to the bass node being at 50Hz and the bass still being so clean and textured. It also slams plenty hard, but never comes off as "boomy" or bleeding into the lower mids.
If the Z1R sounds like you have a big subwoofer in your room, the AC sounds like you have two big subs that also help to clean up the bass nodes in your listening space.
2. Midrange and Vocals:
The Z1R's midrange is slightly recessed, which gives it a V-shaped sound signature, though vocals still sound clear and are well presented. The AC, on the other hand, has neutral and balanced lower mids with a more forward and intimate upper midrange, making the presentation of vocals, particularly female vocals, quite immersive.
I find myself preferring the mids on the AC as they come off more "smooth" and analog. Maybe in part due to the bio-cellulose driver. Kind of neat that we're making these comparisons when you think about how bio-cellulose technology was introduced by Sony (IIRC). But, I find that the biocell driver is a bit more agile and detailed than Sony's massive Ti-alloy driver.
3. Treble:
While the Z1R exhibits a bit of treble spike, it's generally smooth and refined. On the other hand, the AC's treble depends on the pads used. With Caldera Thin pads, treble is slightly laid back. However, with the Caldera Suede pads, the treble extends well, neither forward nor relaxed, providing excellent resolution.
The Z1R is so source dependent that when I was opamp rolling the Burson V6 Vivid in my WHAMMY, I thought I may have borked something. The top-end sizzle was that hot -- and that opamp section in that amp is only I/V stage, not output stage.
4. Soundstage and Imaging:
The Z1R boasts a wide soundstage with decent depth, providing an excellent sense of space and instrument placement. The AC’s soundstage is more dependent on the pads used. But, I would say the AC and Z1R both excel in this domain, with the AC edging out the Z1R in that 3D, holographic imaging trick that ZMF are known for.
There's also a slight amount of decay in the AC that comes off as being very organic and natural.
I'm finding myself prefer the AC for gaming/movies over the Z1R as result of the culmination of characteristics above.
5. Comfort and Build:
Both are top-tier. I'm finding the AC to be more comfortable for longer sessions, however. ZMF have really upped their game in this area over the past couple years, and it shows. My Olivewood is slightly heavier than the Z1R, but it wears it extremely well. However, my ears end up sweaty after an hour or so with the Z1R. They don't do that with the AC, I think in part due to the amazing Caldera pads (they're slightly fluted). That said, the Z1R may offer slightly more isolation, but not enough to honestly make an appreciable difference in most settings.
In conclusion, both headphones cater to slightly different sound preferences. The Z1R might appeal more to those preferring a dynamic and somewhat V-shaped sound signature, while the AC would suit listeners who seek more pronounced sub-bass and an intimate upper midrange presentation.
If you can't already tell I love both, but I am finding the AC to be a better pair to my ears. I'm a huge fan of both ZMF and high-end Japanese audio gear, and don't want this comparison to come off like I'm "shilling" for ZMF, because I'm not at all. I have nothing to gain -- I've emptied my personal wallet for all of my gear acquisitions.
As with all things in this hobby, personal preferences matter most.
While my preferences are leaning towards the AC, I could happily live with the Z1R as my primary cans; once they "click" with your ears, things just sound so musical and enjoyable.
