Researchers from the University of California, Berkeley, have developed a new graphene-based earphone-sized speaker - that can actually outperform the best earphones. They say that even with almost no specialized acoustic design, it performs comparably to a high quality commercial headsets (a Sennheiser MX-400 earphone, in fact)
This speaker uses a diaphragm that is made from a multi-layer graphene sheet. The graphene is sandwiched between two electrodes that create a field that oscillates, causing the graphene to vibrate. The performance is so good because graphene is inherently very thin and strong, and it can be configured to have very small effective spring constant - it's the perfect diaphragm material.
The graphene film used by the Berkeley researchers is 30 nm thick and 5 mm in diameter. Another interesting feature of the graphene speaker is that it is very efficient - it converts most of its energy into sound.
This speaker is the world's first to use a graphene diaphragm, but it's not the first speaker to use graphene. In July 2011 researchers from Korea developed a transparent and lightweight speaker that uses a single graphene-oxide covered poly vinylidene fluoride (or PVDF) film. The graphene is coated from both sides - and acts as electrodes that cause the PDVF film to vibrate.