Graphene makes a good choice for a speaker membrane because it’s light, strong, and electrically conductive. That last property means it’s easy to rig up an electrostatic speaker like the one in this experiment. The 7mm wide graphene film was sandwiched between two silicon electrodes. When current is applied to the membrane, an electrostatic force causes vibrations that can be carefully controlled.
The overall quality of a speaker can be described by its frequency response. Ideally, a speaker should produce sound just as well at every frequency — from low pitch 20Hz all the way to high pitch 20KHz. This would result in a very flat line on the frequency response graph seen above. The graphene speaker was found to perform very well compared to Sennheiser MX 400. The low end is almost the same, but the higher end (more vibration) is much better with the graphene membranes.
Granted, the MX 400s are not amazing, high-end earphones (they retailed for about $20 new), but remember the graphene speaker was not tuned or optimized in any way. The researchers believe that standard techniques for producing graphene can be scaled up to make larger speaker diaphragms out of the material. Unlike applications in semiconductors and displays, a few impurities won’t render graphene unusable for speakers.