Make sound waves visible with this awesome device called a vibration speaker. It turns practically any surface into a larger speaker. The audio jack connects to standard audio output sockets. Stick the speaker onto a variety of surfaces and objects to find out which materials produce the best sound.
Experiment to see sound waves ripple through a tray of sand, water, and other substances.
With signal generating apps, you can experiment to visualize different sound wave patterns.
Recommended age is 8+.