Chapter 7 — Boundaries, diffraction, and modes

What sound does when it meets something.

A sound wave that meets a wall, an interface, an edge, or an aperture does one or more of the things in this chapter: it reflects, refracts, transmits, diffracts, or — when many reflections combine — settles into a standing pattern called a mode. All of these are consequences of the same wave equation applied with different boundary conditions. The chapter unifies them through the Huygens construction.

• 7.1 Reflection at a boundary (normal incidence)
• 7.2 Oblique incidence and Snell for sound
• 7.3 Transmission through a thin layer
• 7.4 Huygens construction — one primitive, three phenomena
• 7.5 Diffraction at an edge and through an aperture
• 7.6 Modes of a 1-D tube
• 7.7 Modes of a rectangular cavity
• 7.8 Room modes and modal density
• 7.9 Reverberation as superposition