SCIENCE - Gel-based audio speaker demonstrates capabilities of ionic conductors, long thought limited in application (w/ Video) Aug 29, 2013 Read more at: http://phys.org/news/2013-08-gel-based-audio-speaker-capabilities-ionic.html#jCp

In a materials science laboratory at Harvard University, a transparent disk connected to a laptop fills the room with music—it's the "Morning" prelude from Peer Gynt, played on an ionic speaker.

http://phys.org/news/2013-08-gel-based-audio-speaker-capabilities-ioni