Bounded sound waves change impedance with tube area, causing reflections

Evidence

This means that for bounded waves, the impedance depends on the surface area within the bounding structure and so will change as the area changes. As we shall see later, changes in impedance can cause reflections. This effect is important in the design and function of many musical instruments, as discussed in Chapter 4. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 174

Note that the acoustic impedance for a wave in free space is also dependent only on the characteristics of the propagating medium. … This means that for bounded waves, the impedance depends on the surface area within the bounding structure and so will change as the area changes. As we shall see later, changes in impedance can cause reflections. This effect is important in the design and function of many musical instruments, as discussed in Chapter 4. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 172

Categorization

• XREF: Connects to the mechanics of wind instruments and how bore shape produces tone in Chapter 4. — connects to: Constricting a tube at a pressure antinode leaves the frequency unchanged; Impedance mismatch determines whether a sound pulse reflects or passes; Pipe walls raise air impedance by reflecting pressure pulses back in phase (+8 more)
• corroborated: 4 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 174; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 172

Broader Connections

• Sound waves reflecting between two boundaries can form standing waves #expands (0.85) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 386
• In-pressure-zone rooms sources radiate less sound due to altered acoustic impedance #contradicts (0.75)
• Waves transitioning from bounded to unbounded space create interfering reflections #qualifies (0.72)