The most dynamic speaker you've heard...

All the technical info and how it relates to a speaker sounding dynamic is great, but I find it very interesting that you equate "dynamic" with "the sound of a pretty soprano piercing my [your] heart". That is a perspective that I can relate to. The sound of a pretty soprano is not the musical example usually used to discuss dynamics; if one is used at all. When a speaker sounds alive it doesn't matter wether it is particularly extended (in either direction), nor is necessarily able to play very loud. The problem that I have found is that many of the most alive sounding speakers that I have heard (usually horns), are not very "pretty" sounding tonally. Since assembling a satisfying system is always about compromise somewhere in the chain, and mixing tonal flavors (wether we want to admit it or not), I have found the solution to be a reasonably dynamic speaker (not necessarily the "most" dynamic) with good tonality well matched to tube amplification which to my ears tends to have more of that elusive "alive" sound than most ss.

Having said that, the "most dynamic" speaker I have ever heard was the Jadis Eurythmie; but I hated how they sounded tonally. Give me electrostats with well matched tubes any day.

The most dynamic speaker I have heard was a one-of-a-kind put together by DejaVu Audio in McLean Va. It used a Western Electric 22A midrange horn with WE 555 driver, supplemented by a Jensen 302A HF horn and a 15" Jensen woofer in a sealed cabinet. As I said, this was the most dynamic sound I have heard....BUT I ultimately preferred the dynamics of my own system. Here's why.

The DejaVu speaker had explosive dynamics in the midrange but the cone woofer, as good as it was, wasn't able to match the same dynamics. This caused what I now call "incoherent dynamics" because different tonal regions had different dynamic qualities.

In contrast, my 2-way speakers (Jensen 15" woofer and an Altec/WE 32 horn with Altec 802 driver) do not have the same explosive quality in the mids but the dynamics are pretty much the same across the entire tonal spectrum. To my ears, the dynamics on my speakers are more satisfying because they are coherent. I think I would find the dynamics of the 22A horn distracting over the long term.

Horns....

I do realize it is an old thread, but I figured it won't hurt to write my input.  

The most dynamic speakers I have heard are the ones I am using at this time, PIERRE ETIENNE LEON M II. You have to hear these.

The B & W 801 S3, I don't want to rule them out, but I feel they were a very large for my mid size room.  

The other thing is that you have to have a good amp as well, or you would not be able to hear the full dynamics of your speakers. 

Focal  Maestro.