Resonators amplify sound by capturing near-field energy and reradiating it with a phase shift

Evidence

A nearly self-canceling (short-circuiting) dipole source (like the wooden marimba key) or quadrupole sound source (like a vibrating cup or bowl, as we show shortly) is actually quite loud in places very near the source— the near-field region. A resonator exposed to the near field is the key to amplifying the sound. Here, we have the real reason why marimba resonators work: the energy in the near field is captured and then reradiated with a phase shift, foiling the short-circuiting. The reradiated amplitude may add partly constructively with the formerly out-of-phase part of near field. We call this the NFC mechanism: short for near-field capture, phase shift, and reemit. The marimba and many other instruments and devices work this way. — Eric J. Heller, Why You Hear What You Hear- An…, 1888

Categorization

• DEFINE: Introduces and defines the NFC mechanism as the actual reason marimba resonators work.