“N Waves” from Bursting Balloons

When a round balloon is burst “perfectly,” the resulting acoustic disturbance should have the shape of the letter N. In the experiments reported here, the N wave is received by a baffled microphone, whose frequency-response characteristic is flat to about 80 kHz. The oscillogram of the microphone output is then photographed. The waveforms obtained show deviations from the idealized N shape, which are attributed to loss of spherical symmetry. Important factors determining the departure from spherical symmetry are the type of balloon and the method of bursting. By paying careful attention to experimental technique and photographing the waveforms from many balloons, it is possible to obtain good approximations of the N shape.