When sound waves encounter a sound barrier during propagation, three phenomena will occur: reflection, transmission, and diffraction. Usually, the barrier can prevent the propagation of direct sound and make the transmitted sound sufficiently attenuated, while the influence of the transmitted sound can be ignored. Therefore, the sound insulation effect of the sound barrier can generally be expressed by the noise reduction amount, which reflects the above two shielding and sound transmission abilities of the sound barrier. Insert a sound barrier between the sound source and the receiving point. Assuming that the barrier is infinitely long, the sound waves can only diffract over the top of the barrier, and a sound shadow area is formed behind it, just like a light is blocked by an object to form a shadow. In this sound shadow area, people can feel that the noise is significantly reduced. This is the noise reduction effect of the sound barrier.