Conventional loudspeakers work by passing a current though a coil near a magnet. The current creates its own magnetic field and so is pushed or pulled by the magnet. If you keep changing the current you will move the coil backwards and forwards creating vibrations in the air, and with the right set of currents, music. However, as you have probably noticed loudspeakers are large and unwieldy things.
Chinese researchers may have come up with an alternative. They have produced sheets of roughly-aligned 10 nanometre carbon nanotubes. They then applied an electric current to the fabric and sound came out. This was quite surprising so they tried to work out what was causing the sound. They shone lasers at the surface of the material and it appears that it isn't actually moving. What is happening instead is that it is heating and cooling from room temperature to 80 Celsius hundreds of times a second. This heats and cools the air close to it which causes it to expand and contract: creating vibrations and therefore sound.
This is not a new effect. It was first noticed over a hundred years ago by passing large currents though platinum foils. However, because it takes a lot of energy to heat up platinum it was immensely inefficient. It takes 260 times less energy to heat up this nanotube material by 1°C and it has a large surface area. As a result it efficiently heats the air and will work a lot better.
The material is transparent so it could be added to the front of an LCD screen on a phone and it is flexible so it could be placed on curve.