The biggest cause of woofer failure is from its inability to dissipate the power that is being transmitted to it. With the incredible power capabilities of today's modern amplifiers, and the drive to achieve higher and higher SPL numbers, people are driving their woofers with the highest levels of power ever. A single driver in a highly competitive SPL vehicle may receive in the neighborhood of 15,000 Watts or more.
Sadly, even the most efficient of conventional loudspeakers has an efficiency of no more than 1.5%. In fact, SPL woofers are typically less efficient as their components are oversized to handling the extreme stresses they undergo during competition.
In the past five years, manufacturers have taken upon themselves the task of greatly increasing a drivers ability to dissipate this wasted energy, which manifests itself in the form of heat.
One of the most popular cooling methods that has been implemented has been spider plateau cooling vents. Speakers have had vented pole pieces for along time. This is a hole in the T-yoke that allows hot air under the dust cap, and on the inside of the voice coil to escape. The air is driven out by the motion of the woofer itself. Spider plateau venting involves a series of holes or vents that allows hot air to escape from the outside of the voice coil. The space between the top of the top-plate and the spider has a series of vents that allows the hot air to escape. I first saw this cooling method on the six-sided Xtant woofers. A similar design incorporated cooling vents in the top plate itself, as found in the massively powerful MMATS Audio Juggernaut competition woofer.
Another area of power handling problems that has greatly improved has been in the voice coil itself. Pioneer has introduced a ceramic coated aluminum voice coil winding to deal with the incredible amounts of power that it receives.
In an effort to improve efficiency, there have been several other improvements that have been implemented. SPL woofers are using square and rectangular copper and aluminum voice coil windings. This increases the amount of copper exposed, as the gaps between the windings are reduced, and theoretically increases the magnetic field strength. One company was even working on an edge wound SPL woofer. I don't know if they released it though.
There are a few woofers, JBL and MTX for example, the use multiple voice coils and multiple (or tall) magnet structures to improve efficiency, and also dissipate the thermal load over a larger area.
The use of exotic cone materials was pioneered by Precision Power as a Carbon-Fiber / Nomex honeycomb flat panel cone. Precision Power is no longer using this technology, but Phoenix Golf and Elemental Designs has taken up where they left off with a Nomex flat panel on their woofers. These are some of the best sounding woofers I have ever auditioned, and are well worth looking at. Remember, ignore speaker design, pay attention only to how well a driver performs. The Elemental Designs drivers are designed primarily for Sound Quality applications, but the flat panel dust cap on the Phoenix Gold woofers have had some good success in SPL applications at the hands of fellow Canadian Moe Sabourin in his Honda Civic.