Background and listening experience: I bought these as a complementary headphone for my ZMF Vibros. I wanted something open and I've been curious about Audio Technica for a while. In the past, I've owned the MDR-V6, DT-990 Pro, Q701, and HE-400. Listening was done straight off my laptop as well as through my Concero to Ember desktop setup.
Overall: I'm very pleased with these headphones for the price. I would not hesitate to recommend these to anyone making a first headphone purchase, as long as you are not looking for monster bass. The fact that they can reach 99% of their full potential without an amp makes them a particularly practical choice. The AD-900x is a clean, open sounding headphone with natural timbre, relatively unfatiguing treble, and a moderate but still satisfying bass response. I particularly enjoy it with ambient, IDM, and all sorts of folk, rock and metal. I don't listen to much classical or jazz but I think it's well suited to those genres too.
Bass: The bass is satisfying for most genres aside from rap and bass-driven EDM like dubstep. It's clean and tight with excellent impact and decent though somewhat rolled-off extension. These headphones put more emphasis on percussion and snap than on rumble. Drums and other acoustic instruments sound fantastic. Note that I am using a wide-bandwidth EQ bump of about 2 db centered at 35hz--this really brought the bass up from meh to satisfying for me.
They can certainly reproduce sub bass but it falls back in the mix and doesn't give the music as much foundation as, say, the HE-400. The Q701 digs down maybe a tiny bit deeper, but the AD-900X has substantially better punch and impact. It actually comes pretty close to the HE-400 in terms of punch but doesn't have the same effortless, visceral sense of texture.
Mids: Fantastic. The mids are slightly forward and have a natural timbre. Acoustic guitars, voices, etc. come forward in the mix, but not too forward--they are emphasized but not enough to throw the balance off IMO.
Treble: These headphones are bright but not excessively bright. I find the treble less fatiguing than any of the other headphones I've owned aside from the ZMF. After EQing the 9khz region down by about 2 db, the highs are smooth and sweet. Sibilance still rears its head occasionally on bright material but it is mild.
Soundstage: Excellent. These have a very wide and deep soundstage, but they don't sound distant like the Q701 either--some sounds are close to you, others are far away in the background, others are in between. I'm still not sure if I know what "airy" sounds like, but these have a very open, spacey kind of sound. Diffuse is a good word.
Imaging: I wouldn't say the imaging is bad, but these headphones have a unique approach to imaging. The sound is very diffuse--you can tell that different parts of a mix are coming from separate locations, but at the same time, the exact location is not clear. For example, the HE-400s are much better at giving me those moments where it sounds like something is behind me and I turn the music off to check. AD-900X positioning is less precise and doesn't have those moments where it tricks you, even though it has a larger soundstage than the HE-400.
Resolution and detail retrieval: I'm not sure what to think here. On the one hand, these headphones have revealed details that I've never noticed before, even through the HE-400. I think the huge soundstage helps there--it makes certain background noises very easy to pick out.
At the same time, my biggest complaint with these headphones is that they are grainy and lack microdetail. They just can't render sonic texture and inner detail with the delicacy, richness, and subtlety of the HE-400, for example. Instead, sounds have a papery sort of flat one-note texture to them. A little hard, but not offensive or metallic. The sonic pixels just aren't fine enough. Honestly, though, I think the resolution is fine for the price and more or less on par with the DT-990 and Q701. It's just that, IMO, this is the primary area where the AD-900X falls short of higher-end models like the HE-400 or ZMF.
Amping: These don't need an amp at all. They sound 99% as good straight from my laptop as they do from my Concero and Project Ember. They are very efficient, but I think this also has something to with the lack of resolution mentioned above--they just can't reveal everything the Concero picks up.
Also, I didn't like them at all using the 0.1 ohm output resistance setting of the Ember. The bass was anemic. They sound much better with the 30 ohm setting (the sound at this setting is similar to my laptop). They sounded fine through my phone as well.
Comfort: The AD-900X is supremely comfortable. I can barely feel them on my head. It seems like the 3D wings don't do much and the clamp is the main thing keeping them on. Since they are so light, I don't even notice the clamp after a few seconds though.
Build quality: OK but not great. They are made from plain matte plastic and they seem to be put together well enough, but their light weight combined with all the swiveling parts also makes them feel a little rickety. The Q701 is almost as light but its construction is more solid and its materials feel more premium.
Overall: I'm very pleased with these headphones for the price. I would not hesitate to recommend these to anyone making a first headphone purchase, as long as you are not looking for monster bass. The fact that they can reach 99% of their full potential without an amp makes them a particularly practical choice. The AD-900x is a clean, open sounding headphone with natural timbre, relatively unfatiguing treble, and a moderate but still satisfying bass response. I particularly enjoy it with ambient, IDM, and all sorts of folk, rock and metal. I don't listen to much classical or jazz but I think it's well suited to those genres too.
Bass: The bass is satisfying for most genres aside from rap and bass-driven EDM like dubstep. It's clean and tight with excellent impact and decent though somewhat rolled-off extension. These headphones put more emphasis on percussion and snap than on rumble. Drums and other acoustic instruments sound fantastic. Note that I am using a wide-bandwidth EQ bump of about 2 db centered at 35hz--this really brought the bass up from meh to satisfying for me.
They can certainly reproduce sub bass but it falls back in the mix and doesn't give the music as much foundation as, say, the HE-400. The Q701 digs down maybe a tiny bit deeper, but the AD-900X has substantially better punch and impact. It actually comes pretty close to the HE-400 in terms of punch but doesn't have the same effortless, visceral sense of texture.
Mids: Fantastic. The mids are slightly forward and have a natural timbre. Acoustic guitars, voices, etc. come forward in the mix, but not too forward--they are emphasized but not enough to throw the balance off IMO.
Treble: These headphones are bright but not excessively bright. I find the treble less fatiguing than any of the other headphones I've owned aside from the ZMF. After EQing the 9khz region down by about 2 db, the highs are smooth and sweet. Sibilance still rears its head occasionally on bright material but it is mild.
Soundstage: Excellent. These have a very wide and deep soundstage, but they don't sound distant like the Q701 either--some sounds are close to you, others are far away in the background, others are in between. I'm still not sure if I know what "airy" sounds like, but these have a very open, spacey kind of sound. Diffuse is a good word.
Imaging: I wouldn't say the imaging is bad, but these headphones have a unique approach to imaging. The sound is very diffuse--you can tell that different parts of a mix are coming from separate locations, but at the same time, the exact location is not clear. For example, the HE-400s are much better at giving me those moments where it sounds like something is behind me and I turn the music off to check. AD-900X positioning is less precise and doesn't have those moments where it tricks you, even though it has a larger soundstage than the HE-400.
Resolution and detail retrieval: I'm not sure what to think here. On the one hand, these headphones have revealed details that I've never noticed before, even through the HE-400. I think the huge soundstage helps there--it makes certain background noises very easy to pick out.
At the same time, my biggest complaint with these headphones is that they are grainy and lack microdetail. They just can't render sonic texture and inner detail with the delicacy, richness, and subtlety of the HE-400, for example. Instead, sounds have a papery sort of flat one-note texture to them. A little hard, but not offensive or metallic. The sonic pixels just aren't fine enough. Honestly, though, I think the resolution is fine for the price and more or less on par with the DT-990 and Q701. It's just that, IMO, this is the primary area where the AD-900X falls short of higher-end models like the HE-400 or ZMF.
Amping: These don't need an amp at all. They sound 99% as good straight from my laptop as they do from my Concero and Project Ember. They are very efficient, but I think this also has something to with the lack of resolution mentioned above--they just can't reveal everything the Concero picks up.
Also, I didn't like them at all using the 0.1 ohm output resistance setting of the Ember. The bass was anemic. They sound much better with the 30 ohm setting (the sound at this setting is similar to my laptop). They sounded fine through my phone as well.
Comfort: The AD-900X is supremely comfortable. I can barely feel them on my head. It seems like the 3D wings don't do much and the clamp is the main thing keeping them on. Since they are so light, I don't even notice the clamp after a few seconds though.
Build quality: OK but not great. They are made from plain matte plastic and they seem to be put together well enough, but their light weight combined with all the swiveling parts also makes them feel a little rickety. The Q701 is almost as light but its construction is more solid and its materials feel more premium.