Explain the Resonance of Sound in Air Columns

Wind instruments use vibrations in air columns to generate notes. The end that air is blown into is all time considered an open end that should have an antinode in a standing wave. A few instruments, such as a flute or saxophone, have both ends of their air column open, thus the only natural frequencies picked are those which permit an antinode at each end.

The air columns of organs comprise one open end and one closed end, thus the standing waves should have a node at one end and an antinode at the other end.

This is as well the case in a common laboratory demonstration, finding the height of water in a glass tube which will generate a sound of a given frequency: alternatively, you are finding the displacement of air that generates that frequency. Generally you then use this information to compute the speed of sound in the laboratory. The sound of a set frequency is generally generated by making a tuning fork vibrate. As water is gradually let out of the tube, the air column will arrives a length at which the set frequency sound can resonate. The resonant frequency is most simply detected by moving the tuning fork away from the tube and listening as you move it back over the top of the tube. If the sound turns into very much louder as you move the tuning fork over the air, you should made the air column the right length for your set frequency to be a standing wave in the air column.