The feedback from this is both unpleasant and damaging to the system. The Lissajous generator centers itself when powered up, but after it has modulated a few sounds the center tends to drift down. So be ready to readjust the tripod at any time. Begin by asking the kids if they know what sound is, or how sound is made. Explain that sound is made when things move .
Vibration is just a word that means moving back and forth.
Have the kids put their hands over their throats and hum so they can feel the vibrations. When they vibrate, they move the air molecules right next to them. These molecules bump into the ones next to them, and so on. This is how sound moves through the air. Pretty soon some of the vibrations have traveled all the way to your ear.