Flue pipes sound through a self-oscillating vortex called the air reed.
Evidence
The preferred explanation is illustrated in Figure 4.14, and it is described in relation to the sequence of snapshots in the figure as follows. Air flows to one side of the obstruction, causing a local increase in pressure on that side of it. This local pressure increase causes air in its local vicinity to be moved out of the way, and some finds its way in a circular motion into the pipe via the mouth. This has the effect of “bending” the main stream of air increasingly, until it flips into the pipe. The process repeats itself, only this time the local pressure increase causes air to move in a circular motion out of the pipe via the mouth, gradually bending the main airstream until it flips outside the pipe again. The cycle then repeats, providing a periodic sound source to the pipe itself. This process is sometimes referred to as a vibrating “air reed” due to the regular flipping to and fro of the airstream. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1141
Categorization
- DEFINE: Explains the air-reed mechanism as alternating pressure vortices flipping the airstream.
- XREF: The flipping airstream as an acoustic oscillator parallels how the louvers/airflow described in the reader’s silence books (e.g., keynote sounds and wind tuning) might physically arise — cross-domain link to The Soundscape’s keynote winds. — connects to: Air reed oscillation is driven by pressure pulse reflections at the pipe mouth — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1159; A flue pipe’s sound arises from air passing a slit and striking a wedge; Reflected pulses at the flue end flip the air reed’s oscillation direction — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1159 (+6 more)
Broader Connections
- Air reed oscillation is driven by pressure pulse reflections at the pipe mouth
#expands(0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1159 - Reflected pulses at the flue end flip the air reed’s oscillation direction
#expands(0.82) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1159 - Reed oscillation is self-sustaining through a positive feedback loop of airflow and pressure
#expands(0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1227 - Air reed frequency rises with airflow velocity and falls with cut-up length
#expands(0.80) - A flue pipe’s sound arises from air passing a slit and striking a wedge
#expands(0.78) - Wind instruments divide into reed and non-reed sound-source types
#qualifies(0.78) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1160 - Organ pipes exemplify both reed and flue wind-instrument sound sources
#qualifies(0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1133 - Lips only begin oscillating as a reed once airflow passes a threshold
#corroborates(0.75) — David Howard, Jamie Angus, coustics and Psychoacoustics, 1263 - Reed oscillation is a damped spring cycle renewed by airflow
#complicates(0.72) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1199