Most people today will (rightly or wrongly) probably associate folded‑ribbon tweeter technology with the Adam brand, but the technology actually goes back to 1973 and a Dr Oskar Heil, who also invented the Field Effect Transistor or FET. Heil's 'Air Motion Transfomer' (AMT) design uses a ribbon material placed between the poles of very strong Neodymium magnets. However, instead of operating as a simple flat piston (like a ribbon mic's diaphragm) the AMT's ribbon diaphragm is deeply folded, a bit like a concertina. In the case of the Elac Jet III incarnation used in The Rock, those folds are only 0.84mm wide.
As the audio signal current flows around the ribbon folds, it interacts with the magnetic field and forces the folds to move in such a way that they actually 'pump' the air in and out, rather than just pushing it back and forth. This configuration makes the design much more efficient than a simple planar ribbon, and because the diaphragm is also the motor, there's a much lower moving mass involved than any moving‑coil driven cone or dome tweeter design. Interestingly, the actual diaphragm movement is also much smaller and slower than a conventional driver (roughly four times slower than the sound it produces), and this results in a better transient response, wider bandwidth (up to 50kHz in this case) and lower distortion than a conventional cone or dome tweeter, as well as better power efficiency.