Tuned mass dampers are incredible. Who knew that hanging a weight within a large structure in just the right way can make the structure more vibration-resistant? You may have seen the one inside Taipei 101 (1,2) but did you know it was also used (and banned?!) in F1 cars? (3,4)

I know what you're thinking. Can we use one to control vibrations in 3d printers, and therefore increase print speed. Have no fear, this lad right here has got you covered: https://www.reddit.com/r/3Dprinting/comments/kvibcj/was_curious_how_a_tuned_mass_dampener_would/

Jokes aside, it does seem to have been used with some reported success in the New Nine 3d printer, but it doesn't seem to have been more widely adopted: https://futureentech.com/easilybuild-brings-revolutionary-new/

I wonder if the double pendulum can apply to the extruder, but instead of the being outside fixed and the inside moving, have the inside (with the filament, heatsink, hotend, etc) stable and the outside (with the fans, and anything else possible) moving.

If I got you curious enough about Tuned Mass Dampers, this here video is pretty effective in demonstrating the concept in detail:

Assuming a 3d printed TDM can be made for a 3d printer, the hope is that much of the "rigidity" infrastructure can be removed, mostly metal parts, making more and more parts of the printer printable, and/or allowing higher speeds for the same design.