Similar to the paper speakers these wood speakers are created by carving or laser engraving a spiral shape into wood that has been prepared with a highly conductive layer. If you then run a 5-9V amplified sound signal through this coil and hold a magnet close to the center of the coil then it will make sound. Unlike most speakers that have the wire coil wrapped cylindrically and placed around the magnet, here the coil is in the plane and part of the membrane that moves the air creating sound.
For more details please see the paper speaker post:
Lasercut and engraved
Inspired by Jean-Babtiste Labrune’s wood flexure speaker structures.
Link to flexure design >> http://dl.dropbox.com/u/9029347/FlexureSpeakerBC1.svg
Styrofoam plate speaker Instructable >> http://www.instructables.com/id/Styrofoam-Plate-Speaker/
Presentation from Open Course Ware class on flexures taught by Martin Culpepper at MIT >> http://ocw.mit.edu/courses/mechanical-engineering/2-72-elements-of-mechanical-design-spring-2009/lecture-notes/MIT2_72s09_lec08.pdf