i know what causes them to blow but what actully happens to the speaker when it happens?
chris m is pretty much right on the money. also, a speaker rely's on the changing magnetic field of the voice coil moving through the magnet to clamp the current through each cycle. If your playing distortion, the cone isn't moving for that brief second and current is allowed to rape that voice coil. that's why it gets hot.
sometimes, with some speakers, you can blow your speaker by overloading its mechanical limits, so the voice coil hits the bottom of magnetic gap, or leaves basket by jumping out of it with cuted rubber and spider funny to see but not so. it's dead, and most of car speakers have no recone kits so you can throw it in a bin. but basically, its by overheating - described once, no need to repeat.
Well it would usually be something like the capacitors that blow in a sub, in a speaker it'd be the crossover usually.
Heat is what causes speakers to blow. The voice coil of a speaker is nothing but a cardboard tube with fine wire winding around it. When you run heavy distortion into the speaker, the voice coil gets hot. If too hot, it melts and creates either a dead short or becomes open and nothing passes. The burnt smell that comes from the speaker is usually the cardboard coating on the tube burning.
