Any discontinuity in a medium reflects an incident wavefront

Evidence

In Figure 2.8c, the mass–spring medium (such as a rope) is terminated rigidly. The discontinuity of the medium causes a reflection of the wave at the termination. As will be shown below, any discontinuity of the medium can result in full or partial reflection of a wavefront. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 175

Categorization

• XREF: Underpins echo and reverberation in rooms, and impedance matching in the ear — discontinuities at the eardrum and cochlear boundaries matter for hearing.