This is incorrect. The speed of a woofer is directly related to its transient response which is dictated by the rate of change of current thru the voice coil. And since a voice coil is essentially an inductor, and inductors don't like the current to change thru them, the higher the inductance, the slower this rate of current change thru the coil and the "slower" the transient response or speed of the woofer. The transient response is also directly related to the frequency response. If you compare two similar size woofer's responses, one with a longer, higher inductance VC and one with a shorter, lower inductance VC, you notice the frequency response of the shorter coil extends higher. Mass has nothing to do with it. Mass does effect sensitivity and resonance but not speed. It is a constant in the force equation, as is BL (Motor strength- assuming it's a well designed motor). The rate of change in current is proportional to the acceleration of the system which is directly affected by the voice coil's inductance. Put simpler, speed and acceleration are time variant parameters. So when you say the "speed" of a woofer is pretty much the magnetic force (BL) divided by the moving mass, you have a quotient derived by dividing two constants. There isn't a time variant parameter to be found in this equation.