Woodwind reeds act as pressure-controlled valves while flue instruments act as flow-controlled valves

Evidence

Woodwind reed instruments make use of either a single or a double vibrating reed sound source that controls the flow of air from the player’s lungs to the instrument. The action of a vibrating reed at the end of a pipe is controlled as a function of the relative air pressure on either side of it in terms of when it opens and closes. It is therefore usually described as a pressure-controlled valve, and the reed end of the pipe acts as a stopped end (pressure antinode and velocity node—see Figure 4.18). Note that although the reed opens and closes such that airflow is not always zero, the reed opening is very much smaller than the pipe diameter elsewhere, making a stopped end reasonable. This is in direct contrast to the air reed in woodwind flue instruments such as the flute and recorder (see earlier), which, as a flow-controlled valve, provides a velocity antinode and a pressure node, and where the flue end of the pipe acts as an open end (see Figure 4.18). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1209

Categorization

• DEFINE: Clarifies the distinction between pressure-controlled (reed) and flow-controlled (flue) valve mechanisms fundamental to woodwind acoustics.
• XREF: Connects to the earlier flute/recorder air-reed discussion in prior chapters of this book; also makes intelligible why oboe reeds double over mouthpiece geometry. — connects to: Brass instruments operate acoustically as stopped-end tubes driven by lip reeds — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1234