RESONANCE FOR SOUND WAVES
Just as standing waves can be set up on a vibrating string, standing sound waves
can be established within an enclosure. In the figure below, a vibrating source at
one end of an air-filled tube produces sound waves that travel the length of the tube.
These waves reflect off the far end, and the superposition of the forward and
reflected waves can produce a standing wave pattern if the length of the tube and
the frequency of the waves are related in a certain way.
Notice that air molecules at the far end of the tube can’t oscillate horizontally
because they’re up against a wall. So the far end of the tube is a displacement node.
But the other end of the tube (where the vibrating source is located) is a
displacement antinode. A standing wave with one antinode (A) and one node
position (N) can be shown as follows: