I don't agree on the probability of amplifier clipping. If you listen very carefully to an amp at the edge of clipping you'll notice slight brightening of sound . This is a very dependable clue to back off the volume and save the tweeter. At the later stage of clipping the sound will become excessively distorted, the treble will become metallic and piercing.

In case of Joel, the problem is loss of treble, not brightening of sound.