Some Notes and Details:
So first thing's first: this project turned out a bit quieter than I'd have hoped, but considering this started off as a sort of a weird hybrid of a concept for a 3D printed drum and a concept for a 3D printed solenoid... I'm pretty happy with it.
The basic idea here is sort of a primitive "moving iron" speaker, where the magnet is attached to a diaphragm, and an electromagnet [speaker coil] applies a varying magnetic field. This moves the magnet/diaphragm and pushes the air, or in the case of an exciter, it vibrates the substrate or plate that you've placed the exciter on.
Winding the bobbin in this project until it's "full" of 28 gauge magnet wire, should get you in the ballpark of 16 ohms, depending on enamel thickness, etc. - which can be driven by most audio power amplifiers.
For those looking to make or modify this design:
As mentioned, there's a lot of room for improvement, so I've left an assembly as a .step file in case anyone wants to make mods in their favorite CAD software. If you've got flexible filament, I think separating that cone into multiple parts, and making it more "speaker-like" could go a long way.
I think one low-hanging fruit if you want to take a similar approach to this design, might be to try thinning out the cone a little bit more (the diaphragm is currently 0.3mm thickness, but I've successfully printed "drumskins" with 0.1mm - it's just a challenge to get these off the print bed)!
Check out the build video if you're interested in seeing how it was made: