Nonlinear vibrating systems generate sum, difference, and combination frequencies

Evidence

It fits a very pretty physical phenomenon that is nearly universal for physical systems that vibrate: nonlinear generation of harmonics and combination tones. Due to this effect, a vibrating system can be driven at one frequency and generate other frequencies spontaneously. If the vibrational amplitude is large enough, new frequencies are generated that are combinations and differences of multiples of the frequencies that were originally present. Thus, if we force a nonlinear system with sinusoidal frequencies f1 and f2, we might see, for example, a new sinusoidal frequency f = f2 – f1 generated as a response. — Eric J. Heller, Why You Hear What You Hear- An…, 2285

Categorization

• DEFINE: Defines nonlinear frequency generation (combination tones) and the difference-frequency mechanism.