An interaction of echoes that leads to reinforcement rather than to partial or total cancellation is known as:

• A. Refraction
• B. Constructive interference
• C. Destructive interference
• D. Autocorrelation

Answer: (B)

Constructive interference occurs when two waves meet in phase, so their crests align with crests and troughs align with troughs. In echoes, when overlapping waves line up in phase, they add together and produce a stronger, reinforced signal rather than canceling out. That reinforces the echo rather than reducing it, which is why this interaction is called constructive interference. Refraction changes direction, not amplitude in the overlapping sense. Destructive interference would weaken or cancel the signal where peaks meet troughs. Autocorrelation is a signal-processing concept that compares a signal with a delayed version of itself, not the physical overlap of echoes.