The octave-shifted echo likely arose from Bragg-like periodic spacing of plantation trees

Evidence

The irony is that a much more plausible explanation of the harmonic echo involves the principles of Bragg scattering, the effect for which Bragg received the Nobel Prize! Sir William may not have noticed an additional clue that Rayleigh left us: the forest causing the echo was “a plantation of trees”—that is, a rectangular array of equally spaced trees. Park personnel at Bedgebury confirm that terminology and the history of regular arrays of trees there. Some orderly plantations of trees can still be seen in Google Earth photos of Bedgebury (figure 28.8). — Eric J. Heller, Why You Hear What You Hear- An…, 2648

Categorization

• XREF: Bragg scattering of sound by periodic structures echoes the reader’s work on periodic structure resonances and Brillouin zones. — connects to: Open and dense forest canopies create distinct sound atmospheres — Vinson Brown, Reading the Woods: Seeing More in…, 154
• SEED: Angle: how a Nobel-winning optics phenomenon (Bragg scattering) solves a century-old forest-echo mystery Rayleigh himself misdiagnosed.
• SHARE: The irony — Bragg himself repeated Rayleigh’s wrong explanation for the very effect he won the Nobel for — is a lovely nerdy tidbit for a physicist friend.