Wood And Wind instruments
In Lesson 4, resonance of a string causes standing waves to form in the string and this can clearly be seen. This
type of standing wave is formed when both ends are fixed. It would be useful to revise what happens when there
is reflection from at free-end of a string and how the pattern of nodes and anti-nodes changes for a standing
wave formed due to free-end reflection. We use these ideas to explain what happens in wind instruments.
Here the moving air particles create the sound and the standing wave pattern and resonance can not easily be
seen but we show, that resonance can be heard in an air column even if both ends are open. This means that
standing waves are created in an air column where the tube is the length is equal to half the wavelength of the
natural frequency or first harmonic. We show animations of the standing waves that occur in instruments with air
columns open at both ends (e.g. organ pipes) and those open at one end (e.g. recorders and flutes). A pattern
is created by the standing waves. In areas where the air column is open, antinodes develop and where the air
column is closed, nodes develop. Learners are shown how to calculate the correct length of an instrument tube
so that it has a given first harmonic. This lesson ends by exploring the marimbas and an interview with a skilled
player of these wooden instruments.