The simple device described below will let you see the sound waves from your voice transformed into moving patterns of light on a wall. You'll need an empty can with both ends removed, a balloon, scissors, tape, a small piece of foil and a flashlight. Cut the fat end off a balloon. (If you use a fairly big can like we did, you'll need a large round one). Stretch the balloon over one end of the can so it makes a smooth drum-like surface. Attach a small piece of foil to the centre of the balloon. We discovered that the device will work much better if you attach it with a loop of tape from behind. The foil must be able to move with the balloon as it vibrates. Here's how it works. When you make a noise in one end of the can, the sound waves hit the rubber balloon and make it vibrate too, in the exact same pattern as the sounds hitting it. If you reflect a light off the foil from the other side so that the reflected light falls on a white wall, you will see the pattern of light change as you make different sounds. We found that it works best in a dim room with a flashlight. Aim the reflection at the wall until you get a clear pattern from the foil. Then start making noises into the end of the can. We got the best results when singing, with the can tight to the face. You can easily see different patterns as your voice gets louder and softer, and especially so when you sing different notes. It would also be interesting to see the result if the light source were a laser pointer! It would be fascinating to try beaming the light pattern at a light-sensitive cell that would produce a varying electric current as the different sounds hit it. This in fact is the principle behind fibre-optic voice communications (if you ignore the fact that we aren't sending the light through a tube). Resources