Acoustic resonance enhancement is used to purify tones by suppressing contaminating frequencies.

Evidence

Resonance enhancement by NFC played a large role in production of pure sinusoidal tones, necessary for careful psychophysical studies. The Helmholtz resonance enhancement of a partial—one frequency—made any contaminating frequencies in the source all the less important. Even today, distortion lurks in the finest electronic equipment, and it is hard to be sure that only a pure sinusoidal tone is produced. Using inexpensive electronics, extreme distortion including harmonic generation can easily result, as was done deliberately in creating figure 25.6. — Eric J. Heller, Why You Hear What You Hear- An…, 1904

Categorization

• XREF: Ties to Chapter 16’s discussion of tube modes and resonators; also connects to the reader’s general listening question about why resonators shape perceived timbre.