It's also an open-back design, so its sound will be audible to anyone within a few feet. On a positive note, a key advantage of open-back headphones is that they're arguably safer to use in public, since it allows ambient sound to enter from your surroundings, though, as I mentioned, the audio quality isn't ideal.
The first thing you'll notice about the sound of these headphones is their exceptional detail, but you'll never experience listening fatigue even after hours of use -- that's because the HE-400's sound is beautifully balanced from the deepest bass to highest treble. Switching over to the Shure SRH1440 full-size headphones the sound appears "closer," less spacious, and less rich.
The HE-400s' bass is also notably articulate and deep, without a hint of muddiness. Compared with the pricier Grado RS 1i headphones, the HE-400s' soft-to-loud dynamics are more explosively alive and the bass oomph is stronger. The HE-400s rock harder, but also sound equally poised at low, moderate, and loud volume levels.
Radiohead's guitarist Jonny Greenwood wrote the orchestral score for the film "There Will Be Blood," and the HE-400 proves its mettle on the sound of the strings. The orchestra sounded perfectly natural with no hardness or glare. And when playing DJ Krush's ambient trip-hop, the headphones projected a huge soundstage beyond the confines of the earcups -- the HE-400 really does sound great with all kinds of music.
At home, the headphones work best with receivers and headphone amplifiers like the $399 CEtrance DACport. And although the HE-400 isn't optimized for use with portable music players, it certainly sounds acceptable plugged into my iPod Classic. Power is the first issue, however, and it can't play nearly as loud with the iPod or phones as it does with a home theater receiver. Still, bass impact and overall clarity are better at home, though I wouldn't totally rule out occasionally playing the HE-400 on the go.
The HiFiMan HE-400 looks, feels, and sounds like a much more expensive set of headphones. They're sure to please audiophiles with sophisticated tastes, and they sound remarkably spacious, making the HE-400s ideal for home theater duty. The HE-400s' only real limitation is their lack of synergy with on-the-go portable use. Other than that one caveat, they're highly recommended.