This is a trick that is somewhat well known, but not often used. Say you have a snare that wasn't recorded with a bottom mic, or the snare you have doesn't have enough snare rattle...
This is the process of placing a speaker on top of a snare, sending the snare signal to it, and putting a mic on the bottom. It works really good and allows you to recreate the sound of snares that were never recorded. You can adjust the tightness of the snares for more or less rattle.
It even works great for drum machines. We are actually using room mics with it as well to get more snare room sound on other tracks.
(please forgive the poor phone photo)