Correlated sound sources cancel at points where path difference equals half a wavelength

Evidence

Consider the situation shown in Figure 1.25, which shows two correlated sources feeding sound into a room. When the listening point is equidistant from the two sources (P1), the two sources add constructively because they are in phase. If one moves to another point (P2), which is not equidistant, the waves no longer necessarily add constructively. In fact, if the path difference is equal to half a wavelength, then the two waves will add destructively, and there will be no net pressure amplitude at that point. This effect is called interference, because correlated waves interfere with each other; note that this effect does not occur for uncorrelated sources. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 360

Categorization

• DEFINE: Defines acoustic interference as a phenomenon requiring correlated sources and geometric path differences.
• XREF: This half-wavelength cancellation ties to standing waves and room mode text that likely appears in later chapters on room acoustics.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 360