Originally Posted by warrenpchi
If we go by http://www.head-fi.org/a/describing-sound-a-glossary
Transparent - Easy to hear into the music, detailed, clear, not muddy. Wide flat frequency response, sharp time response, very low distortion and noise. A hear through quality that is akin to clarity and reveals all aspects of detail.
Open - Sound which has height and "air", relates to clean upper midrange and treble.
"Open" needs a third attribute: it needs good treble extension (mainly 12-18kHz) that is relatively flat. HE400s aren't great but are better than most in that aspect.
It still has peaks and small ringing ridges (around 13kHz) which cause a little tizz, but otherwise it gives the sound signature a lot of air.
In comparison, HE500s:
Notice how it has a pretty big chunk of upper treble missing, that helps give it a very forgiving tonality especially with harsh vocal recordings. However the downside is it contributes to the headphones not sounding as open as something like the HE400.
A third comparison would be something like SR007mk2.5, which is reputed to have some of the most airy "materialize-out-of-thin-air" sound possible:
Notice just how clean, even, and nice the upper treble is extended, and that it is relatively emphasized. The lack of peak/ringing means even with the emphasis it is still not tizzy, and the emphasis relates to how there is huge amounts of air in its presentation.
Admittedly I have not had a chance to audition high-end STAXs yet, only the Hifiman and Audeze planar lines (all of them), but there is a perfect correspondance with their measurements and my subjective impressions of their treble behavior and "openness", so I thought it'd be fair to extrapolate a bit.
Edited by jerg - 12/1/12 at 1:57pm