In March of this year, researchers at the University of California Berkeley published a paper demonstrating the use of graphene to build a set of Electrostatic loudspeakers which would be good for use as in-ear headphones. They compared the performance to a set of (cheap) sennheiser earbuds and found reasonable comparable performance. The key benefits appear to be extremely low power / high efficiency and good high frequency response.
can be exceedingly high (close to 1) because the power dissipation path is almost pure air damping, which converts the mechanical vibration of diaphragm to sound. Magnetic coil type earphones (the type used today for virtually all earphone applications) typically have efficiencies <0.1.
3a) is markedly better than that for the MX-400 thanks to the extremely low-mass diaphragm. In the low frequency region, the EDGS and MX-400 response curves both bend downward, largely due to limited capability of the sensing microphone and restricted coupling between the speaker and microphone.
ExtremeTech has a write up summarizing the paper.
We can probably expect more work in this area to refine the design for commercial use in the future.