Science Forums 2

[Pyrotex]

stretch a thick plastic film very tightly on a large rigid circular frame -- like a meter-wide steel ring -- making something very like the head of a drum. Mount the film horizontally and place a speaker cone underneath. Sprinkle some contrasting powder on the film -- if the film is white, use black powder (like pepper) or if it's dark, use a white powder (like salt).

Play constant sounds through the speaker, and see if the powder clumps together at the film's static nodes of vibration. It should if you increase the volume, and if the speaker is close enough to the film.

For sounds, begin with pure sine-wave tones. Try different frequencies. Then combine two different sine-wave tones. See if there's any difference when the two pure tones "harmonize together" and when they sound discordant (clash). Use a digital camera or phone camera to capture the powder patterns on the film. Analyze these patterns. Determine what they tell you about the sounds being used.