Short term, recoverable effects:
Severe compression and distortion. This can happen as the signal approaches the physical limits of the drivers, without permanent damage.
Voice coil overheating can also cause compression effects over longer periods of time. So pro / PA gear has to deal with proper driver motor venting and cooling.
Permanent failure modes:
Cone over-excursion: The force can actually make the coil/cone ballistic.
Overheating voice coil: The insulating enamel melts, shorts and loose it’s ability to create a strong enough magnetic field to push against the permanent magnet, while at the same time reducing the speaker impedance, possibly damaging an amplifier.
Wiring fuses, or opens, preventing the amplifier signal from flowing, so, no sound.
Shorting or opening of the crossover components, including coils, caps and resistors, causing either no sound at all or possibly all the sound reaching the driver. In any event, the speaker sounds wrong. Can cause secondary effect of too much power reaching a delicate driver, tweeters especially, thereby causing the driver to fail as well.
Best,
E
