...because there's no more juice...
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So, if there is no more juice than why is there a concern of blowing the speaker?
The fear of blowing a speaker with a weak amplifier is often overblown
. If you have a 300 W or 400 W rated speaker what harm can be done from a 50W amplifier? A 50W amplifier can not put out more than 50W, period. The speaker woun't even break a sweat.
A real danger comes from 'matching' amplifier and speaker. For instance, if you have a 200W rated speaker and 200W amplifier than you have to watch for clipping. Clipping distorts the waveform and add tons of higher harmonics. That's why clipping sounds raspy. These harmonics are re-directed by the crossover circuits to the tweeters and there is enough juice to burn them.
