My sources are: Cowon S9, Cowon X7 (that very quality player) and Samsung Galaxy S2 (whose primary purpose, of course, quite another is to play as music). My Compare properties in the in-ear range are: Denon AH-C 751, Klipsch S4a (already anything but cheap earplugs).
At the Cowons manage the Sony-listeners who ask Denon and Klipsch clearly in the shadows. Of course, no worlds between these three listeners. But Sony manages the virtues of Denon (spatiality, nearly linear frequency response, precision) and Klipsch (liveliness, power bass) to combine and even better to implement at least one step in each case.
The frequency response is linear as with anything else I know of in-ear (the equalizer of Cowons therefore remains consistently in neutral position). Treble and midrange are absolutely clean. The bass is incredibly present and strong, but never intrusive. The different levels of music are clearly worked out, the space is absolutely amazing for an in-ear. It's just fun. :-)
The sound of a high quality "big" headphones (eg Beyerdynamic DT-990) should not be expected anyway. It still lacks long way to airiness and sovereignty, with the example, DT-990 airs, but the Sony's are pretty damn close, and certainly irritate the currently feasible in In-Ear-segment.
Among the included ear pieces should find the right for him every user. The fit in the ear is impeccable and comfortable. Even several hours listening sessions to give rise to red ears to be (unless one hears too loud, but that's another topic).
The efficiency of the Sony handset is good, not quite as loud as the Klipsch, but rather adequate to the level of Denon, definitely. The Sony benefits from an external headphone amplifier (he then acts a trace airy and sovereign), but this is not an absolute must.
I want to leave unmentioned that you probably did not quite so much fun at a less good source. Compared with the Cowons the Galaxy S2 coincides with the Sony headphones a bit off, a difference that I have not seen so dramatically with the Denon or the Klipsch. My favorite on Galaxy S2 therefore remain the Klipsch.
The Sony just exposes any weakness, and in one (albeit high-end) Smartphone not so good audio components are now installed as times in the Cowons. Also, any weakness in the coding of the musical material should immediately stand out (FLAC Lossless formats or similar would be ideal, but perfectly encoded MP3s or OGGs it should be in any case).
A definite recommendation for those with high-quality and high-quality music playback devices material.
