Pros: airy, good bass, cheap for a planar, imaging and soundstage, easy to drive
Cons: not for bassheads, bright, heavy, fatiguing
Build Quality / Design: Metal forks and a nice dark blue finish. The logo paint fades easily, so do not touch it. Pictures you see online don't do these much justice, trust me, they look much better in person. The headband is lacking a bit of padding, but I do not find it uncomfortable at all. These are pretty heavy, but the weight is distributed pretty evenly for me and are comfortable, just not so much as the HD 650 or HD 598. Stock pleather pads cause my ears to sweat after a bit, but velour pads for a mere $10 fix this easily.
Bass: I have to admit, I was a bit underwhelmed by the bass produced by these, especially after hearing about how well orthodynamic headphones do bass. They provide an ample amount for Hip-Hop & Dubstep but impact isn't very low or too high. I was never "wowed" by the bass. It kept its place and never became intrusive unless I equalized them to death. More then enough bass for Jazz and easy listening though. Bass extends low & rolls off after about 30hz, but it just doesn't have the impact I crave unless I EQ these, and the HE-400 can handle the bass being equalized to ridiculously extreme levels.
Midrange: The upper midrange is a bit laid back, but put a pair of velour pads & it becomes more evened out. Vocals feel a little back on some songs, I always thought these were a bit V-Shaped.
Treble: The treble is bright and was almost unbearable the first time I heard them. It has now settled down quite nicely but I would say the treble is still bright. I notice sibilance in some songs as a result of this. I also find the bright treble fatiguing, it was OK at lower volumes but I couldn't stand it at higher volumes.
Sound-stage/Imaging: Moderate size, but the cheaper Q701 & HD 598 had a larger sound-stage. Quality wise, the HE-400 wins. The combination of air, energetic treble, and great layering was a much better experience as a whole, despite it's smaller size. I can easily follow and pinpoint an instrument or sound effect, while I would get lost trying to find them on the HD 598 & Q701.
Amping, Final thoughts: Yes, you can drive these with your laptop, phone, or iPod. The HE-400 was loud and portable sources could handle them. However, sound improves with a dedicated amp. I noticed slightly stronger bass, improved detail, and more sense of air. I really feel that these are a great value because of how well they handle being plugged into multiple sources. They sound great out of my iPod, Phone, 30 year old A/V receiever, and PSP & scale up with my amp nicely. The HE-400 handles every genre I throw at these, ranging from light jazz to heavy metal and can please a wide variety of music genres.
Some songs I have tested. All tests were with velours, Rolls RA53b amp, and FLAC or 320kb MP3's.
Tonight The World Dies, Avenged Sevenfold, Rock
Vocals have sibilance, but sound very realistic. Cymbals and drums crash with authority, perfect amount of bass.
The Quiet Room, L'Orange, Electronic
Large amount of air & great detail. This is a lo-fi track trying to replicate the sound of vinyl, you can hear the smallest details like the scratching of the needle on the vinyl. Easy to follow the voices, piano, and everything in the song.
Everyday My Birthday, J Stalin, Rap
Bass is handled well and extends fully. However it does not "wow" you. It keeps it's place and never invades the rest of the sound spectrum, even though most people who listen to rap would rather have it be more pronounced. Good Imaging makes it easy to find and pinpoint where the rapper is, gunshots in the background, piano in the background, etc. Hi-Hats in the beat are played with authority because of the bright treble. No sibilance at all.
Execution, Andy Stott, Electronic
This song has very low bass. Headphones and even full size sub-woofers have trouble playing this. The HE-400 extended all the way down and was able to play the low bass (Under 40hz). The ambiance of the song surrounded my whole head.
L.A. Noire Theme 9th Minor Extended, Andrew Hale, Jazz
Nice bass that never invades the rest of the sound. Soundstage and imaging is great, you can tell where the violins are, the Sax, piano, etc. All the instruments are rendered nicely and sound realistic. Treble was a bit too bright on some parts of the song, but was never a huge issue.
E Extended Mix, Drunkenmunkey, Techno
Drums and Hi-Hats rendered with authority, strong thumping bass with great speed that was able to keep up.