^^^^^^ What he said -
The first thing is to spend $10 bucks for the velours.
Then, put on some damn good Jazz Music. The HE-400 will, I bet, blow away the Senns. It takes time to appreciate the speed and texture of the Planars - at least a couple weeks. Jazz is what revealed to me their bass texture and higher resolution, then electronic stuff with lots o' bass showed me how much the bass of the HE-400 is really in another league vs. dynamics.
Also, congratulations! You are now probably the 1 millionth person that has come on here "underwhelmed" by the HE-400s yo just bought. Don't worry, like most of us, you are going to see the light eventually and realize these things are actually tons of fun.
The HE-400 are not forgiving headphones and they have resonance issues which IMO is the worst aspect overall - the FR is fine and the "treble spike" so often fixated on is pretty moot except for the occasional track. In any case, a simple 2-3dB cut is approximately all I've ever needed to cure that little issue.
I use mine with the O2/ODAC and the pairing is excellent. Unfortunately most of the recordings that may be tolerable to you on lessor phones probably sound horrible on the HE-400s. Garbage in - Garbage out. Its just true - too many albums I own are awesome but unfortunately just don't sound all that great.
I'm just going to send them back while I still can honestly. If my musical selection is not compatible with them then I'd just as soon grab a headphone which works for what I like rather than have to switch music to suit the headphones. I tried them with many different genres though, just to test them out and I just didn't care for the sound at all. Keep in mind, I didn't try them out on trash. I tried them with FLAC and 320kbps MP3. I couldn't stand the sound of the MoFi Beck - Sea Change album through them. I don't think that album can be placed in the "garbage" category! It's one of the best sounding albums I've ever heard and I love it, but I actually found it unbearable due to the unnatural sound the HE-400 produced. I also use the O2/ODAC btw.
Honestly, everything sounded significantly more natural in my HD-600's. I find that I can focus on any part of the music with them and nothing is thrown in my face in a harsh manner. The HE-400 sounds darker, and yet it has this section of the FR curve which is in my face, scraping away at my ear drums. The velour earpads probably help the HE-400, but I just don't find the FR curve to be to my liking and I'm not convinced that their character will change that drastically with the different pads. The reason I'm fixating on that odd spike is that it is not a moot point with any of my music. I find it physically uncomfortable and distracting. Perhaps I am just very sensitive to this frequency, but it is physically uncomfortable to me. I notice it in every single song I've heard and EQing just seems to make them sound even more unnatural and withdrawn. I could not EQ them to my satisfaction honestly. Plus, I don't find them all that comfortable anyway.
I prefer the HD-600 so much that I would never use the HE-400's for any purpose. Hopefully that doesn't upset people, but it is my experience so far. I also don't actually find the bass lacking on the HD-600. It doesn't extend quite as low as the HE-400, but I find the quality of the bass on the HD-600 to be spectacular. I am able to pick out bass notes clearly and precisely and I find it quite natural sounding, just without as much sub bass performance. Plus, my M50x's have plenty of that ear thumping punch if I really want it. I'm probably going to try the HD-650 out a second headphone so I can have a slightly different sound from a headphone I already love and my fiancee can also enjoy them.
This isn't a knock on anyone who likes the HE-400, I just don't. I think that some headphones just don't sound right to some people. I find it odd that there are people who don't like the HD-600, but they are definitely out there. My personal preference is toward the sound of the HD-600. I find that it sounds good with every genre because of its natural sound and the fact that it doesn't overemphasize anything too much. It also works really well for movies, shows, games, etc. I tried the HE-400's for these purposes as well and was disappointed because again they did not sound natural to me. Even $1000+ headphones have people who love them and people who hate them. Much of it is about personal preference. The good thing is that I know a little more about my own preferences as a result of this experience.
Edited by shawtuw - Yesterday at 1:06 pm