Opposite-phase monopole sources cancel at a distance when separated by less than a wavelength

Evidence

We need only to check the sound intensity some distance away from the source. We can use the superposition principle, the same principle that lets us add two waves to get a resultant wave; here, we add the pressure patterns from each of the two sources. If the wavelength is large compared to the spacing between the sources, the sound pressure fields from each source are almost equal and opposite at any point some distance away. The two monopole waves making up the dipole source waves almost cancel, making the sound much less loud. — Eric J. Heller, Why You Hear What You Hear- An…, 605

Categorization

• DEFINE: Explains superposition and dipole cancellation mechanism in clear, physics-grounded terms.