I did this too for an architecture thesis-ish thing. Trying to experiment with self-regulation and analog feedback. Wild to see that you're doing it too. May I ask your intentions?
Mine didn't work well. I was using a pan on a speaker, not the actual cone so I didn't ruin it, but the results were pretty lackluster. I couldn't get enough volume to actually get much result in the starch (and the pan probably muted some of it). I think to really get it to work well, one would have to use a car stereo speaker or something with a lot of travel. I was also using a waveform generator, so I could get really pure low tones which made patterns, but the variation of music I think is responsible for some of the more dynamic forms that you see on youtube.
This was one of those 2am things... someone overheard that I was making ooblek in order to visualize the resonant tones that I have been assaulting the 9th floor of Wurster Hall with. So she came over and we watched a few cornstarch monster videos on youtube and, damn the thesis, I was going to have some fun. I managed to produce one monster before I blew out one speaker. Then the next morning, with one of my advisors and a crowd of people watching, it failed to produce the monster... and then the second speaker blew out.