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

Another way of talking about "speed" is "lack of stored energy."

That is, the waterfall plot is very clean and very short, without ringing.

Not to brag, but...

My subwoofers are so fast, they can do a 20-cycle sine wave in a MERE fifty milliseconds.

Not only that, I’ll go out on a limb and claim NOBODY makes a subwoofer that can complete a 20-cycle sine wave in less time than mine.

;^)

Seriously, I agree with those who have noted in various ways that what happens with the trailing edge of the note - how quickly and cleanly it decays - is (in general) more important than what happens at the leading edge of the note, at least when it comes to the subjective impression of "speed".

Duke

Another way of talking about "speed" is "lack of stored energy."

I supposed that has more to do with "driver break up" or suffering from "impedance anomaly".  Paper cones may have a clean water fall plot, but an aluminum cones may have "faster speed" but may not look as clean on the water fall plot.  

Of course having "faster speed" does not always mean "better".  There word "speed" in this thread seems to have a lot of different interpretations.  Different people seem to have different impression of the word.

Now I get. The view perpendicular to the revolution is opposite except in  the downward position.  

i think speed in a speaker mostly refers to the mid and upper bass 50hz-250hz region which are the power frequencies where the music lives. vocals, drum kits, pianos, cellos, horns.....they all fall down or rise in this area.

leading edge precision and the presence or lack there of ease and refinement in these frequencies either impart flow and energy to the music and maintain the timing or muddle and restrict that flow and energy.

this is a speaker-amplifier-room issue, not just the speaker. and typically you see a crossover right here, amps struggle controlling the drivers here, and rooms have most of their worst bass nodes in this area. as you increase the dynamics and SPL’s this will be where things go to hell first as the combination of the speaker’s limitations, the amp and the room acoustics all rear their ugly heads.

but get the crossover out of this region, have sufficient driver surface to limit the need for much excursion, and appropriate amplifier for the speaker draw, solve the room issues, and you can get the ease and effortlessness and the speed and precision of the music will result in that speed that serves the music, the music breathes and soars.