So, here's the set-up: A small stereo speaker is connected to a function generator. A concave lens, bearing a ball is place over the speaker. Now, the frequency is slowly increased in the function generator. My question is, Will the ball really bounce at a certain frequency? Because I am not really sure about it. I just a found that set-up from a problem in a book and I want to try it for my research. And also, if it will bounce, what causes it to bounce? Is it the vibration of the lens?