The most dynamic speaker you've heard...

A field coil driver uses an electromagnet (coil of wire carrying a current that creates a magnetic field) in place of the permanent magnet of a regular driver. This type of driver requires a power supply to energize the coil creating the magnetic field.

The field coil drivers I've heard were quite lively sounding (very dynamic). Old examples would include the Western Electric 555 driver, and modern examples include the woofer in the top line JM labs speakers and all of the drivers in the big Classic Audio speakers, and certain Feastrix full range drivers.

There are so many things that have to be right to get the most out of a field coil driver, particularly the power supply. I was really surprised how different these speakers sound with different power supplies.

I haven't found any speaker that has exhibited exceptional dynamics under all conditions. Great horn drivers are truly exceptional at lower volume levels and can make music sound lively and engaging at surprisingly low levels, but, they tend to "shout" a bit when pushed to higher volumes. A lot of the the dynamic speakers people have been listing above are good at higher volumes, but sound lifeless when played at softer volumes. The same goes, to me, with the MBL speakers--great at higher volumes, but not the best at lower volume.

Some horn and field coil speakers, like the Classic Audio T-1, sound very good across a surprisingly wide range of volume.

I rarely listen at high volume levels so I have gone with fairly high efficiency speakers that exhibit great dynamics at lower volume. My midrange is a Western Electric 713b driver, the woofer and tweeter are modern high efficiency models. The 713b is a fantastic driver, but, it does exhibit a bit of "shouty" quality when played at high volume (not dramatically so, but noticeable). Everything in audio involves so kind of tradeooff, so personal priorities are important.