In-phase sounds double while out-of-phase sounds cancel to silence

Evidence

Because a sound wave has periodicity, the pressure from the different sources may have a different sign and amplitude depending on their relative phase. For example, if two equal-amplitude sounds arrive in phase, then their pressures add and the result is a pressure amplitude at that point of twice the single source. However, if they are out of phase, the result will be a pressure amplitude at that point of zero, as the pressures of the two waves cancel. Figure 1.13 shows these two conditions. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 230

Categorization

• XREF: Phase cancellation is the basis of noise-cancelling headphones and active sound control, connecting to the reader’s broader interest in engineered silence.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 230