How can constructive interference make a sound louder?

Constructive interference makes a sound louder by increasing the amplitude of the resulting sound wave. This occurs when two or more sound waves overlap in space while they are in phase—meaning their crests coincide.12

According to the principle of superposition, when these waves combine, the resulting disturbance is the algebraic sum of the individual disturbances. Because the amplitude of a sound wave determines its intensity, which is perceived by the human ear as loudness, the reinforcement of these amplitudes creates a louder sound than that of the individual waves alone.13