Propagation speed is also influenced by the strength of the driver magnetic field, the level of travel control, the rate of recovery, the level of speaker deformation, and a multitude of cone and driver behaviours.
Keep in mind that these behaviours don't occur in unitary fashion, but many, many times over a period of a minute during a song. The woofer cones we deal with have a feedback mechanism internal to the cone, they have a feedback mechanism with the surround, they have a feedback mechanism with the voice coil and magnet assembly, they have a feedback mechanism with the speaker enclosure, and a feedback mechanism with the amplifier. A woofer that is not designed to account for all these interactions is going to reveal shortcomings along the path, ones that allow it to work within design parameters with ease, or fail at multiple facets.
Fast bass allows the woofer to recover and reproduce the next impulse event in the shortest period, or number of cycles, possible. Conversely, a woofer that is not rigorously designed can still be dealing with the first propogation event five beats later. This is the basis for fast bass vs bloated bass.