Pressure feedback drives the reed into full closure across each cycle

Evidence

The gap between the reed and shallot is narrow, and for air to flow, there must be a higher pressure in the boot than in the shallot, which tends to close the reed fractionally, resulting in the gap between the reed and shallot being narrowed. When the gap is narrowed, the airflow rate is increased and the pressure difference that supports this higher airflow is raised. The increase in pressure difference exerts a slightly greater closing force on the reed, and this series of events continues, accelerating the reed toward the shallot until it hits the edge of the shallot, closing the gap completely and rapidly. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1198

Categorization

• XREF: A positive-feedback mechanism, same family as squeal in audio amplification; parallels spontaneous oscillation in hearing mechanics. — connects to: Positive feedback drives the reed to slam shut — David Howard, Jamie Angus, coustics and Psychoacoustics, 1227