The ESP Guitar Company

Howdy Lads, was having a jam with a mate the other night when he went to shift his speaker cab around to face us, while doing this the power lead from his preamp slightly came out of the socket, when he pushed it back in an extremely loud, and i mean LOUD "pop" came through the speaker, I have heard that this can damage the speaker, it still sounds fine, but how can you tell if it's damaged/or not? The cab has Celestions in it. Anyone in the know? Thanks lads.