I'm sure this topic has been looked at at great length but I was asked about it since I've owned both the HE-400 from Hifiman and HD650 from Sennheiser and here is part of the conversation that we had. I hope this helps!! To set things up, he was curious about why I was selling my HE-400's and how they compared to the HD650's I purchased.
Here we go!
Selling the He-400's was not an easy thing to do, Simply put, they're amazing. So the question is why did I sell them? (for the 3rd time btw) They just were not what I was looking for at the time I owned them. The sound is undeniably one of the best you can get for under $500 so its tough to say weather or not the HD650 sound better overall but there are some very clear advantages that I noticed the second I put the 650's on.
First is the comfort. Hands down they are 10 times more comfortable than the 400's and a lot easier to wear for hours and hours on end. The first night they arrived they were a little stiff and had a strong clamp but that went away in the first hour or two and after that, I didn't take them off for probably 5-6 hours straight no joke. Even while I was watching TV I just turned off my music and left them on. The first few weeks I owned them I didn't touch another headphone.
Second is probably the main reason why I got ride of the HE-400's again. They're not easy to drive properly. Orthos are known for being power hungry despite the lower impedance ratings. The HD650's are rated at 300ohm but they can be powered fairly easy and will improve based off of your source. All I have at the moment (Upgraded since this conversation) is a Fiio E17 and e9k that I'm probably going to sell or send back because I don't really need it at the time (the E9k) and the returned money will go towards a better amp like Schiit Valhalla or Audio-GD 15.32. (Didn't end up with either one of those, instead got a EF5, Arrow 3G Fournier HTA-2, and Burson HA-160DS)
Once I get the right amp I'll probably buy them again or go after either the HE-500's or LCD 2's (Got the LCD 2.2's) because the sound is just so damn good top to glorious bottom with the Orthos, but until then the 650's are the far better option for me at this time and here's why. They are exactly what I love about closed cans but in the open format so I get a better sound stage and I don't feel so closed off to the world around me all the time. The bass is close to being on par with the 400's just not as deep or fast so if the 400's bass is rated a 8.5/10 the HD650's are 8./10. The mids are probably a toss up which is a great compliment to each can. But the highs are definitely in the corner of the 400's, it's a much more lively can than the HD650. The HD650 is about as laid back as you can get. Now to some this may be the opposite because they can be a little to bright so this one really depends on your personal preference.
Overall its a really hard choice from the sound alone but from everything else around it the HD650 is the better option. Well at least it was for me, but if you have a great amp with enough kick to put the Orthos in their place you may have a totally different opinion than mine.
Next he asked me about the e17 and the types of music he listens to. Rock Rap Dub and D&B and if either one is capable of keeping up with the fast paced music and violent drops...
The E17 as amazing as it is had some issues pushing the HE-400's. For example with the HD650's with 12db gain and the volume at 20, it wasn't super loud but it was getting there. The 400's with the same settings was a whisper. You have to move it to 30+ to get things kicking. The issue with that is you'll start to hear obvious and clear distortion coming from the e17 because its trying to hard to push them. Now the E09k on the other hand... No problem whatsoever powering the HE-400's or even the LCD 2's! The e09k with either e07k or e17 stacked is hands down for the money the best you can buy. I listen to the same kind of music that you do so I can't have a headphone in my house that can't handle sudden and ridicules drops you know. I have evolved as a bass head but its still going to be one if it not most important part of a can for me. They both are more than adequate in this department. The HE-400's have better Sub-bass and the HD650's have better mid bass. So the HD650's bass though not as deep or as fast is slightly more prominent but the depth and speed goes to the HE-400's.
Honestly, you couldn't go wrong with either one. Sound stage, Imaging, and separation also a toss up. Sound Stage I'll give it to the HD650's but imaging and instrument separation goes to HE-400's. But again though this is nothing against the HD650's which need very little help to sound amazing. You can have amazing results outta a JDS LADS cMoyBB with the 650's vs needing an amp with a lot more power to push the 400's
In closing both are amazing and you really can't go wrong with either one but it is very important to understand before hand which sound suits you best. If you want the can with more sparkle and deeper bass the HE-400's are the right ones for you, but if you're looking for something laid back with amazing mids and all day comfort that can be outstanding with any genre of music the HD650 is your can.
Even though I have since upgraded to the LCD 2.2's I still can't get over the overall package of the 650's. Simply amazing and you can get them used for around $350 and for that price you can't go wrong. I hope this help some of you out there looking into either one of these cans.
Equipment used. HE-400, HD650, Fiio E17, Fiio E09k, HP Pavilion G6, Foobar2000 w/ Flac files to 320kbps
Thanks for the read!