Idea: Resonant weight

Old idea. A voice coil with a weight would be attached to a surface. The weight would oscillate and tune to the frequency of the surface it was attached to, creating the most noise/vibration possible! Lots of mischievous uses (what if you attached it to a piece of plate glass!).

Might have some use in vibration testing, where it would find all of the vibration frequencies, and give you the ability to do sweeps. Might save time for package designers that don’t have access to a vibration table?