This video shows the motion of a Celestion CF1025C compared with that of a competitor's driver of similar specification, They are both shown in this laser scan, reproducing a 1400Hz signal.
The competitor unit demonstrates several distinct radial modes with the motion of the cone edge/surround lagging being the motion of the cone body. Conversely the CF10 motion is relatively pistonic, moving back and forth in a more linear fashion. This is demonstrated by the consistency of colour in the scan.
It is the linearity, the pistonic motion that is most desirable when developing a PA speaker, it makes the sound output clearer, more accurate and more and pleasing to listen to.