ZMF Aeolus, aka open Atticus, aka Areolus, aka Nips. Zach sent me a finalized pair for review. He will either be sending Marv a pair soon or have me ship this unit his way. If you wish Sony could make an MDR-Z1R with some actual thought and refinement put into it, get an Aeolus. If you like to EQ up the bass on your HD650, get an Aeolus. If you want a more refined sounding Fostex TH-X00 or wish you could capture the sound of the Creative Aurvana Live in Big-Boy Version, get the Aeolus. Your new savior is Zach, "the finest manufacture of Japanese headphones." (credit to @purr1n) Besides, aren't nipples a gift, after all? Sound The Aeolus is a lush (read: warm, bassy), very dynamic, and engaging sounding headphone and not at all ashamed of its nature. It's not exactly basshead-level, but it sits in between the HD650 and typical basshead. (Talking stock HD650, here.) Going back and forth between it and the HD650 makes the HD650 sound decisively midrange-focused, grey, veiled, and boring. Of course, there's no doubt the Aeolus is the more colored headphone, given its additional bass and slightly more "flavorful" treble presentation. The midrange and treble isn't as smooth, coherent, and balanced as the HD650, but it's pretty similar. It just has more flair to it. With all the extra bass presence on the Aeolus, I find the quality to be perhaps roughly on par with that of the HD650's. In some regards, it sounds a little faster, tighter, and better controlled, but it still has that somewhat loose and bloomy quality to it. As a whole, I guess it's a little better in some ways, but no worse in other ways. I do find it easier to track the low-end on the Aeolus and find it more authoritative overall. Still, that could just be because there is more of it and not so much that it is of better quality. If nothing else, you do get real bass extension here. The upper-mids through treble are more similar to that of the HD650, but there is something in the the upper-mids or lower-treble that sounds very slightly nasally or hashy. This is subtle, and I never had any issues with it myself, but it is there nonetheless. It's just a little more noticeable than the HD650's 5KHz love bump. In most music, you might just hear a bit of extra presence or definition. Other times, you might get a hint of things not sounding quite as coherent or normal as on the HD650. It never really bothered me. Listen to the crowd clapping at the start of the live "Hotel California" on both headphones, and you'll hear what I mean. The Aeolus sounds wider than the HD650, but it is also more forward and aggressive overall in its presentation. I think it handles layering a bit better despite being more forward. Resolution is about on par between the Aeolus and HD650, which is to say excellent. The Aeolus sounds clearer and less grey at first, but when you really dissect your music, you find they perform about on par with the smallest details and nuances. And as fun as the Aeolus can sound, it never really compresses stuff up or down. It handles the macro and micro stuff as expected. When comparing the two, the HD650 is like a well-calibrated LCD TV with lacking contrast ratio due to grey blacks. The Aeolus is like an OLED TV with some of the naughty, incorrect picture options turned on that the average consumer seems to enjoy so much for reasons I can't understand (or do I understand, given I like the Aeolus?). Anyway, Aeolus = better contrast ratio, punchier, but technically not as accurate. It just pops more. It sounds faster, clearer, less veiled, less grey, and overall more dynamic, even if it's not as truthful in reality. So, at the end of the day, you end up with a very tasteful, fun headphone, sort of an HD650/Z1R hybrid that retains the technical chops of the Sennheiser. I really liked the Aeolus at RMAF, and I really like it here at home. It's not going to replace my HD650, but it's just a joy to listen to if you don't mind some warmth and color. It's a headphone I actually want to keep around to complement the HD650. It strikes that blend of fun/musical and balanced almost perfectly and has the technical skills to boot. Note: I recommend letting the pads warm up while listening for about 10-15 minutes before critical listening. The leather and memory foam nature of the pads seems to necessitate that. It might help smooth out the sound a bit. It does help with channel inconsistencies caused by cold pads. The ZMF stuff is picky about fit, placement, and seal. Adjust headband shape as needed. Disclaimer: Zach did offer to let me keep either an Auteur or Aeolus as thanks for help I've offered over the years, and I'll probably take him up on an Aeolus. Measurements Frequency response results, left channel, against the HD6XX, show about a consistent 1-2dB increase over the HD6X0's response until about 80-90Hz. From there on, the Aeolus sustains more extension with a more gradual roll-off. It sounds thicker throughout the midrange and has noticeably more bass (quantity and extension). However, the bass emphasis isn't as concentrated as it is on the HD650, so it all blends together better. The response above 1KHz is roughly similar, though you can see the Aeolus is a little less smooth and, most notably, has a couple small hot spots around 6-7KHz. Distortion results are pretty good above 100Hz. A bit of a spike around 3.5KHz, but below 1%. D2 seems similar to that of the HD650 but starts creeping up around 80Hz rather than ~100Hz on HD650. They both cross the 1% mark around the same spot. Interestingly, I am seeing more D3 on the Aeolus than HD650. I will double check these results in the next few days for consistency. Harder to get a consistent readout with these types of pads. Background noise can also be a factor. CSDs look fairly good, though not quite as clean as the HD650's. It looks like the semi-open cup nature may be causing more resonance between 1-5Khz, though it's fairly minimal here. The small 4.5KHz dip on the measurements seems to be a hidden peak or standing wave of sorts. Nothing too alarming, but could be better. (Note that CSDs only look at one measurement take. FR results take a few averages.) Results with a -45dB floor. Really just an extension of what we see above. I do think there might be the slightest ringing in listening, but, again, any issues I noted were so subtle as to not have bothered me while listening. Only slight noticeable. I would not be too concerned by this.