If sound quality and appearances matter to you then you might be interested in this pair's just-announced relative, the HD681 EVO headphones. Unlike the vanilla HD681 model, the EVOs look like a professional piece of equipment and supposedly have a flatter response. Like the HD681s they are semi-open, though.
The Superlux HD681 headphones may look like they cost $30, but they certainly don't sound like it. These are truly "monitor" headphones in that they are designed to expose details in the music, and hence can be ruthless with poorly recorded music. There is a definite boost in the upper-mids that adds a breathiness to vocals and accentuates high-frequency instruments like cymbals. While this can make music sound more exciting, the downside is this can make some music too bright and even uncomfortable to listen to.
"My Number" by British band Foals sounded overly compressed and splashy despite this actually being quite a punchy recording. In comparison, theheadphones sounded more natural, with less emphasis on the mushy hi-hat cymbals.
Despite the hyped upper register, the headphones are balanced elsewhere with a controlled bass response that isn't hyped like some of the other sub-$100 headphones out there. If you like anything with deep bass, dubstep for example, then these headphones will keep the music from closing in upon itself.
Likewise midrange is tight and to the point. Compared with the similarly pricedheadphones, the Superlux HD681s are a revelation: the JVCs are distant-sounding and made the snare drum of Future of the Left's "Plague of Onces" seem like it was coming out of a cardboard tube. The Superluxes are able to convey the -- frankly insane -- song in a much more natural and enticing way.
At $30 there isn't much to compare to the Superlux HD681: these are open-sounding, detailed headphones that are much more balanced than the equivalent JVC HA-RX700s. The issue is that they are not very dynamic and the treble can overwhelm the rest of the spectrum. If you spend a little more you can get a simply great set of headphones in the , but they are much less comfortable.
Are the HD681 headphones a hi-fi bargain? Not quite, and their capacity for modification sounds like bloody-mindedness on behalf of the owner rather than a real benefit. They sound great for the money if you only have $30 -- they could be a "gateway drug" into the world of hi-fi. But if you are willing to spend a little extra I would strongly advise buying a pair of Sony MDR-V6 or Gradoor headphones -- all better-looking and better-sounding.