Tough question, alot of partial answers here. There are different ways a speaker can be blown. It is possible for a speaker to run out of excursion limits (travel), when this happens, you normally would hear a popping sound before it is too severly damaged. That popping is the voice coil former bottoming out against the magnet, then the voice coil is damaged from slapping against the magnet or the cone rips from too much travel as you stated in your question. The most typical problem has been somewhat addressed above by others. Amplifiers are driven to clipping, the voice coils heat up and either come apart or get so hot that they may partially melt and seize the cone. If a cone seizes its obvious, it is frozen (won't move). If the coil has partially come off the former, that is where you will hear a rubbing or garbled sound. As Elizabeth stated, you can put your fingers on both sides of the center of the cone and push evenly, if the coil has shifted, you will hear or feel a rub. If the tweeter is blown, most designs have replaceable diaphrams, its kinda like a recone on a mid or woofer. Reputable woofers and mids have recone kits available. It is very important to get the correct kit, the weight of the cone and stiffness of the surround and other things must all match for the performance to be the same of the original driver. Lastly, it is possible for a component to be bad in the crossover, typically a burnt resistor or a electrolytic cap can burst. So when you say, "what actually happens" it is a very broad question. I have given you a very broad answer, but one that I hope makes sense. Good Luck, Tim
