In reply to:
Bren: what is there about clipping that will damage a speaker? There is all sorts of music with all sorts of wild power/ frequency swings.
The easy answer - when a signal is clipped, it's turned into somewhat of a square wave, which increases all the harmonics in the form of distortion (on a S/S amp - it's odd order distortion and sounds like crap... on a tube amp - it's even order distortion and sounds musical, this distortion is what gives the "tube sound") want to see what clipping looks like on an oscilloscope? Get a piece of letter sized paper, I'll wait.
Got it? Good... now draw a camel's humps - say ten of them... a wavy line about 2" high total, half the humps below an imaginary centre line, half above...
---/\/\/\/\/\--- like that only rounded - there's a sine wave - I drew a triangle wave in ASCII there and if it looked like ---|\|\|\|\--- that would be a sawtooth waveform... anyone that played with early digital synths should recognize those. But I digress. Now draw the same thing, only 12" high (but you're not allowed to go off the page - flatten out the peaks. It's starting to look like a square wave (or pulse wave) now.
But why does a pulse/square wave destroy speakers? Honestly, I'm not sure if anyone knows. Yes, there is a lot more "oomph" to them because of all the harmonics... but as the harmonic intervals get further away from the fundamental (original) wave, they get less powerful very quickly.
In short - I personally can't tell you why it happens, just that it does. Alan? Your opinion?
As for music with "swings" in frequency and amplitude - that's really not what we're talking about here. Well, unless you set the volume for the diminished level and the elevated levels push the amp into a clipping state.