AES = Audio Engineering Society.
One of their many jobs is to maintain standards set for all things audio to ensure compatibility of specs. When it says power rating is x watts AES, it means that the method of testing power handling is the one prescribed by the AES for that purpose. You can see this on other specs in fine print, such as 'T/S parameters have been tested on an AES baffle'.
I believe it's a certain amount of time with pink noise at that power, but I'll have to check.
Beranek\'s law
\'bits of ply round a driver\'
