What does the term "Speed" mean in a speaker?

 As much as I have enjoyed reading through this thread, I couldn't help but remember when Velodyne made subs that used an accelerometer on the woofer cone, allowing it to be 'corrected' by the sub amp 3,500 times per second (maybe that is the way they still operate, dunno). It has been a very long time since I have owned such an animal, but I still remember the speed that I heard in the bass. To me, it came across not only in impact, but pitch definition as well. 
 Years earlier, when I owned a pair of corner horns, the bass had much of this kind of quality too, IIRC. 
 The sub that I am using presently (10" driver with a 12" passive radiator) with a velodyne SMS-1, doesn't have these effects, even though the bass is enhanced (increased).

The TS parameters for bass driver being used in a horn is very different from the same sized driver used elsewhere. For example, the surround of the driver is much stiffer (typically a cloth material), since the cone moves very little. +/- 1/16 was amount stated in the horns that I made.