Acoustic reflections arise at any change in tube cross-sectional area

Evidence

Figure 2.10 and Equation (2.22) on page 27 show us that a plane wave travels in the tube without modification as long as the area is constant, but at any discontinuity of A(x) a part of the wave is reflected back and the rest propagates onwards. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 614

Categorization

• XREF: The impedance-mismatch reflection principle that governs vocal-tract acoustics also drives cochlear impedance matching, transmission-line theory, and architectural acoustics.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 614