One of the challenges any woofer has, in particular subwoofers, is stopping and starting with any degree of accuracy. The mass of the cone on these woofers is high; there's a lot there relative to a tiny tweeter or midrange.
The woofer's motor, not much more than a magnet and coil of wire, takes a good deal of energy to make the cone move. Once in motion, it takes energy to stop its motion and reverse its path. I think of these actions like those of stepping on the gas and brake of a car. Think of how it feels to be in a car when it accelerates and brakes. Your personal mass has a lag time moving forward; as well as a tendency to keep going when the brakes are applied. A woofer's cone has the same issues as those of a passenger in a car.
Imagine for a moment the electrical signal controlling the woofer. The electrical signal demands the woofer move forward a specific distance, then back again; all at a predefined speed. Only, that's not exactly what happens, due to the tendency of the woofer to not want to move when ordered to; and its similar reluctance to stop instantly and return to where it started. To overcome these obstacles you need a good deal of power from your amp and, as well, you'd be better served with something else in the mix; a way to measure the cones movement and compare it to what's being demanded.
That's tomorrow.
