Rubens Tube

Natural gas is flowed into a copper pipe with a series of equally spaced holes. The gas flowing out of the holes may be lit and the height of the resulting flames is an indication of pressure in the pipe at that location.

Sound waves are generated inside the pipe using a sine generator and a speaker mounted at one end. When the sine generator is tuned to a resonant frequency of the pipe, standing waves form and are observed in the flame pattern.

Playing 'Ode to Joy' on the piano gives you nice patterns (ask Sid). Note that the speaker is not too powerful, so that in order to clearly see the pressure nodes, you need to run the gas at low pressure. If you want the note to be audible, you can use an amplifier to separate and amplify the signal, which you can send through a loudspeaker.

L2, A0 or piano in L3

PIRA DCS 3D30.55