[ampair]

apparently, researchers from tsinghua university and foxconn in china have created the first ever earbuds powered by the thermoacoustic effect, i.e. speakers without moving parts:
 
http://cen.acs.org/articles/91/web/2013/09/Rocking-Carbon-Nanotubes.html
 
the spl chart also looks interesting, but at a sensitivity of ~48dB/mW those guys would suck your portable player's/amp's battery dry in no time

 

[wink]

Woeful SPL.
Let's hope the R&D people burn the midnight oil to develop a moer linear graph.