Hey guys, this is going to be my first post here on Head-Fi, but I thought I'd share my impressions on the HE-400i since there doesn't seem to be many reports about this particular headphone. I'll focus on the sound quality here, especially comparing it to the other HiFiMan headphones I also heard while at the T.H.E. show last weekend.
Forgive me if I am unable to fully capture the nuances of the headphones' sound, as this is my first post and because I don't have really that high-end equipment back at home (my most expensive headphone is the Sennheiser HD598).
Be prepared for the massive wall of text that follows (lol).
First, a bit on the comfort of the HE-400i (and the HE-560 as well, since they share the same headband design). These things are extremely comfortable. The HE-400i's in my opinion were the most comfortable planar magnetic headphones at the show - it slightly beats out the HE-560 because of its lighter weight. The HE-400i and HE-560 headband did an excellent job of distributing the weight of the headphones around the head (which isn't that much to beign with, especially compared to the Audezes that were also at the show), and the clamping force was perfect - not too tight, but also not that loose either so the headphones wouldn't just move around while on your head. And the HE-400i and HE-560 were easy to just put on your head and start listening with a good seal - in this respect, this is much improved over the older generation HiFiMan headphones that I was able to sample (I listened to the HE-6 at the HiFiMan table, and the HE-500 at the Schiit table).
As for the HE-400i's sound... I thought it was excellent. Good amounts of treble and mids, but it also has some really awesome bass. I really enjoyed listening to bass guitars and the thump of the kick of drums with this thing - the quality and quantity of bass of this thing is amazing. And while there was lots of bass, I felt that it didn't really bleed into the mids or other frequencies, and it was extremely well controlled.
I wasn't sure what to expect from the mids and highs, given how some people have described how the HE-400 performs with regards to those frequencies. However, I was pleasantly surprised. The mids and highs of the HE-400i sounded natural, and I couldn't detect any real anomalies with it. Vocals on the 400i sounded really good, and I was pleased because this was one of the aspects I really look for in a headphone (also one of the reasons why I really love my HD598's). I wouldn't call this the airiest set of headphones in the world (the HE-560 definitely beat the HE-400i here), but I thought it did well in classical and orchestral music. Violins sounded great on the HE-400i (though I would still have to give the nod to the HE-560 here for a more realistic rendition of violins).
As for the soundstage (general impressions here, I go more into detail below), I was pleasantly suprised by it. I was prepared to be disappointed by the HE-400i's soundstage because I absolutely love the huge soundstage of my HD598's, but I didn't really feel that the HE-400i's soundstage was lacking. True, the 400i's soundstage is definitely smaller overall than the HD598's (especially in terms of width), but I felt that its soundstage exhibited decent depth and good height. The imaging on the 400i's was excellent (but slightly behind the 560's). Overall, I felt that the 400i's have a decently sized sounstage that most importantly is very cohesive (things don't sound so far out there that it doesn't sound good anymore).
Comparisons with other HiFiMan headphones (in addition to what I said above):
HE-400i vs HE-400 - unfortunately, I couldn't find a HE-400 at the T.H.E. Show, so I couldn't compare the HE-400i with its predecessor.
HE-400i vs HE-500 - I thought these two headphones sounded extremely similar to each other (keep in mind I did not listen to both of these headphones on the same setup). Both have plentiful (but not excessive) and excellently controlled bass, and both have very pleasing mids and highs that don't blend into the bass. However, I would have to say that perhaps the HE-500 is very slightly less veiled compared to the HE-400i (though I'm not sure whether this is due to the difference in setups).
HE-400i vs HE-560 - While I think that the HE-560 is technically better than the HE-400i (it definitely was more detailed, and less veiled/transparent compared to the 400i), I wouldn't say that the HE-560 is better in terms of enjoying the music, depending on the listener's preferences. Personally, I feel that the 400i is more of what I'm looking for in a headphone. The HE-400i's soundstage isn't that much smaller than the HE-560's, but it's a lot more intimate. The vocals (and pretty much everything else, including each instrument in an orchestra) in the HE-400i are brought much closer to you than in the HE-560, which I really enjoyed (I love that feeling of the singer seemingly being right in front of me). While I feel that the HE-560's are more detailed and slightly more clearer than the HE-400i (but not by as much as you would think given the difference in prices), I personally prefer the HE-400i because of its more intimate presentation.
Overall, I think the HE-400i's are very impressive, and are really a great value considering how close they sound to the 560's and how they pretty much sound just as good as the HE-500, both of which currently sell for more than what the 400i will cost.