Circular Membrane (drum head) Vibration

A circular membrane (drum head) vibrates with a variety of interesting patterns and shapes, each at their own frequency. In this demonstration I took a 6-inch square of latex rubber dental dam (courtesy of my dentist), stretched it over a short length of 4-inch diameter PVC pipe, and held it in place with rubber bands. I drew some lines and circles on the membrane to help identify vibration shapes. A frequency generator (you could use a computer) provides a sine wave to a loudspeaker. A strobe light was