Researchers at ENSTA Paris have created a loudspeaker without a magnet or copper coil, instead using a simple dielectric elastomer membrane and a conductive grease. Through adding a transmitted electrical signal, the flexible material reacts causing the necessary vibrations to send sound waves, optimising efficiency, spectral balance, and linearity. The newly designed speaker is much lighter than current models, leading to easier and less expensive production. There are however still technical issues with the design, including the membrane being very fragile, but if overcome the system could be massively industrialized at a more affordable cost with less weight, making applications limitless.
https://www.polytechnique-insights.com/en/columns/science/loudspeakers-new-materials-in-acoustics/