What increases when two Soundwaves are out of phase?

When two sound waves are out of phase, specifically by 180 degrees, they can interfere destructively, leading to a reduction or cancellation of sound intensity. This results in a decrease in perceived loudness or even silence if the amplitudes of the waves are equal. Conversely, when they are in phase, constructive interference occurs, increasing the sound intensity and loudness. Thus, the phase relationship significantly affects the resulting sound quality and intensity.