A sound barrier is an obstacle placed between a sound source and a receiver which interrupts the path of the noise. It's always made of sound absorption or sound insulation materials. The sound wave propagates in the air, but when it hits the sound barrier, reflection, transmission and diffraction phenomenon will take place. So there will be an acoustic shadow behind the sound obstacle. In this region, the propagation of the sound wave has a significant additional attenuation resulting in preventing the noise effects on receivers in a certain area.