I have both, they're related sonically but also different. The AO is more balanced with a more traditional mid forward ZMF tuning. The AC has more of a U shaped signature with more emphatic bass (especially subbass). I'd say the treble is actually pretty similar between the two, but the AC's mids are not as forward, giving the initial impression the mids are recessed. They're not, but they're not as forward as the AO. They both have that wonderful natrual biocellulose timbre, which for me is the highlight of the Atrium line. For their similarities though I do think they're different enough to own both. The AC is a bit more aggressive and engaging dynamically. That subbass is pretty epic sounding, with good strong punch and slam, and the perfect amount of decay to sound full and weighty. Today I brought my Audeze LCD2 Closed to work since they get no time anymore. In comparison, they're so much thinner sounding than the AC. The decay is just too fast, and all the weight is lost when those bass notes hit but dissipate almost immediately. Both Atriums have natural decay.
Staging is amazing on the AC, but it is smaller than the AO. That's unavoidable though given the closed cup. How you'll react to that is impossible for me to say. I don't feel like the AC sound closed at all, but I put very little importance on soundstage. All headphones, even open, sound closed off to me as a lifelong speaker listener. The biggest difference between the AO and AC stage-wise is probably the overall dimensionality. The AO puts out a soundstage that feels more 3D, with better spatial placement of each element in the mix. The AC collapses the stage a bit. To me maybe 10-15% smaller, with less precise placement within that smaller stage. For example instruments in an orchestra stand out more and are easier to visualize with the AO than the AC. I don't find the difference significant at all, but others might.
Finally, refinement is higher on the AO IMO. The AC is a bit more aggressive and bombastic. It's more energetic and playful, for lack of a better word. It's more of a party animal to me. The AO parties hard too, but can't quite keep up with the AC, especially down low. The AO's counter though are those wonderful mids. If you're a singer/songwriter lover, the AO IMO is better as the mids are more forward, putting those vocals more forward. The AC's bass can sometimes dominate vocals, especially low male vocals.
I think the AO and AC play best to different genres. I LOVE the AC for metal and rock. That more aggressive and engaging nature pairs wonderfully with fast and exciting genres. But for Jazz, Blues, and vocalists, the AO is my drug of choice. Yeah it does metal/rock well too, but the AC just brings the energy and excitement a bit more.
Finally, sitting here listening to the LCD2 Closed makes me long for the AC. I am listening to the same band I found yesterday, and it's just not as fun or engaging. Here's the band/album if anyone's curious.
The LCD just sounds thin and irritating in comparison. I might be going home at lunch to grab the Atticus or AC! I think I need a giant gear purge, I really only listen to a few headphones these days and the LCD just isn't making the grade anymore. Anyone wanting to buy one, i'll be listing them. First owner, pristine condition. PM me.
Hope some of my nonsense helps.
