Constructive VS Destructive Interference

When the waves strike other waves, instead of reflect they combine to each other. There are two types of interferences, one is constructive interferences and one is destructive interferences. The amplitudes of two waves are same direction (both waves is positive or both negative) so we will combine the two waves together by adding them together is called Constructive interferences. However, if the two amplitudes have opposite direction, we combine those two waves by subtracting. This is called destructive interference. And Constructive interference will make a sound louder while destructive interference will make a sound quieter.