The main cause of subwoofer failure is overdriving or driving a clipped or distorted signal continuously to your sub. This can result in a mechanical or electrical
failure. With electrical failure the result is normally a burnt voice coil causing the sub to go open circuit or in some cases short circuit to ground.
It is important to match the “RMS” ratings of your sub to your amplifier to avoid overdriving. Clipping or distortion is the audible sign of an unclean signal and this can originate from any piece of equipment in the signal chain. What this means is you may be only driving your amplifier at say half power yet your head unit/source may be driving at close to it’s maximum output which could be supplying a clipped or distorted signal to the amp thus creating the audible distortion you hear.
Mechanical failure is when the spider or butyl surround rips or tears or sometimes the voice coil jumps the gap. What we mean by jumps the gap is that when the sub is being mechanically overdriven it can result in over excursion or over travel. This result is the voice coil leaves the gap that it travels in and results in failure.
Mechanical failures in general are all symptoms of over excursion which can be caused by having the wrong size enclosure and or overdriving. It is very important to follow the recommended enclosure volumes to ensure the optimum performance of your sub and to protect it from these types of failures. Another important fact is the port length and diameter in relation to the tuning of the enclosure as this also could adversely affect performance and reliability.