OK, time for my ranking of the six headphone models I've been testing for a while now.
From best to worst (among these six):
1. Abyss Diana
2. Abyss AB-1266
3. Grado SR125e
4. AKG 550
5. Audio Technica ATH-AD2000X
6. Bose NC700
Among these six, Abyss Diana is easily most musically rewarding to my ears. It's not that they have a particularly flashy sound, but rather that they make me engaged in whatever song I play. Things make sense! They have also been the easiest to compare headphone amps with, as musical nuances appear so right - or not quite right - or simply missing (when the amp sounds veiled). Addictive!
The even more expensive Abyss AB-1266 may be more resolving, but they are less down-to-earth than Diana and simply don't swing as well to my ears. Stefan Gürtler, who is the headphone expert at
Concerto Audio said that if AB-1266 performs worse than Diana, the headphone amp is not good enough. While I agree with him that the headphone amp is more important than the headphones (the hierarchy rules), I did try all six headphones with three different amps: Grado RA-1, Naim Headline with NAPSC power supply and my own prototype. My impressions of the differences between AB-1266 and Diana remained the same regardless of which of the three amps I drove them with.
Grado 125e is far below the Abyss headphones, but still a lot of fun. The music is well timed and easy to appreciate. The sound is pretty straightforward and not particularly impressive.
AKG 550 has the most odd sound of these six. Some parts of the frequency spectrum are elevated and other parts feel constrained. They are also closed (but don't isolate you all that much from your surroundings), which likely elevates the odd sound qualities. The music is however well timed and once you forget about the sound (which you will, and much faster than you'd expect) they are quite enjoyable to listen with.
ATH-AD2000X sounds neutral and well balanced. Definitely more so than AKG and perhaps even Grado. They lack some subtlety, however, and don't quite engage me musically as the others do.
Bose NC700, my own pair that I wear daily when walking in traffic and have previously praised, are interestingly the worst performer in this group. There are some things to note here:
1. When I praised them after having done a quick comparison with a few AKG models, I was using an iPad as source and headphone amp. Using a proper source (HAKAI) and headphone amp, the AKG's benefitted
much more than the Bose NC700. Put in another way: The NC700's are forgiving.
2. NC700 was connected by cable, but also need to be switched on. When switched off, they sound very thin and annoying, with no bass at all. When switched on, you will notice that there's a LOT of sound processing going on: It straightens the frequency response and adds noise cancellation (very effective isolation from the outside world). If you decrease the noise cancellation (perhaps thinking it might decrease musical performance), you will notice that this isn't really possible. Instead it adds the sounds from the outside, captured by the microphones, to give you an illusion that you're not wearing the headphones. Noise cancellation and heavy signal processing is
always present, regardless of setting. And this is likely the reason why they are not particularly musical. Things sound pretty nice, but the level of musical finesse is low and the timing is a little off.
3. NC700 are wireless (Bluetooth) and made for listening on the move, not for musical pleasure in your home. Disconnecting the cable and going wireless, they perform pretty much the same. There's a little more bass and the sound is more "fat" in wireless mode. This may actually be even more forgiving with a lesser source. And the quality of the headphone amp when listening wired didn't make much difference - perhaps because what's really driving the membranes is Bose's own battery powered miniature amp module inside the headphones.
(4. I used to have a pair of Bose QC35 before, on which the noise cancellation was actually possible to switch off. I never had the opportunity to compare these two models, but now I'd like to. I've got a suspicion that the QC35 is more musical than the NC700.)