I have long been a fan of quite simple enclosure designs. I have
used acoustic suspension (sealed) and bass reflex (ported) enclosures
in my vehicles for years. All have performed certain tasks very
well, while lacking in certain areas at the same time.
Sound reproduction is based on the laws of physics. If you take into consideration, and account for all the laws, to the best of your abilities, you should end up with a great sounding audio system. Sound is basically a wave traveling through the air. The length of the wave (or frequency) is what causes most of the problems for subwoofer systems in a vehicle. High frequencies have very short wavelengths, while low frequencies are just the opposite. The wavelengths of a deep bass note can be 20, 30 or 40 feet. It is difficult to transmit this wave through the air in any form. (This is why radio stations modulate the information (music) onto a high frequency carrier to transmit it.) There is one advantage of trying to recreate low bass in a car. A small area like the interior cabin of a vehicle exhibits what's known as a transfer function. What does this do for you? It is an inherent gain associated with this small space. And it's what allows a pair of 8-inch woofers to have low frequency output below 25 Hz in a car.
What did you want your system to do? In my case, accuracy is important, but so is having some fun. So I am likely to use a ported enclosure, subwoofers with moderate physical power handling, and supply them with lots of power.
JL Audio specifies a combined physical and thermal power handling rating for all their drivers. In their case, this number represents the amount of power, that, in a properly designed enclosure, will, for 8 hours, not cause any damage to the speaker. They also specify a normal, and long-life power level in their Enclosure design book (see you local JL Audio dealer). The other way of rating power handling is the one that produces the big flashy numbers. Lots of companies list outrageous power handling numbers on their drivers. Numbers between 1,000 and 2,000 Watts are not uncommon. BUT, this number is commonly the amount of heat that the drivers voice coil and magnet assembly can dissipate before causing damage. It does not necessarily describe power that can be absorbed with the driver in any type of enclosure. It also does not provide a length of time at which this level can be maintained. I am not saying that there is anything wrong with this number, but the true useable power handling number must then be calculated from the specific enclosure design you wish to utilize. A drivers suspension will allow it to only move so far before some component (the spider, surround, tinsel leads or voice coil former) is damaged.