Rijke Tube Resonator

The Rijke tube is an interesting example of an open cylinder resonator. Folds of copper screen are positioned about one-fifth of the way up the tube. When the screen is heated in a burner flame and then moved to one side of the flame, it will produce a strong tone at its resonant frequency for several seconds. The standard explanation has to to with the ease of excitation of a system at its resonant frequency. The air which passes up through the red hot screen is heated and expands, producing a pulse of air toward the center of the pipe. Like a push which raises a mass on a spring above its equilibrium position, that pulse of air will start the system into oscillation at its natural frequency. Note from the video clip that the excitation of the pipe depends upon the chimney effect of air moving up the path and the sound stops when the tube is turned horizontal.