声波遇到声屏障时，就会发生反射、透射和绕射三种现象。通常屏障能够阻止直达声的传播，并使透射声有足够的衰减，而透射声的影响可以忽略不计。因此，声屏障的隔声效果一般可采用减噪量表示，它反映了声屏障上述两种屏蔽透声的本领。在声源和接收点之间插入一个声屏障，设屏障无限长，声波只能从屏障上方绕射过去，而在其后形成一个声影区，就象光线被物体遮挡形成一个阴影那样。在这个声影区内，人们可以感到噪声明显地减弱了，这就是声屏障的减噪效果。
When sound waves encounter a sound barrier, there will be three phenomena: reflection, transmission and diffraction. Usually the barrier can prevent the transmission of direct sound and make the transmission sound attenuate enough, and the influence of transmission sound can be neglected. Therefore, the sound insulation effect of the sound barrier can generally be expressed by noise reduction scale, which reflects the above two kinds of sound shielding capabilities of the sound barrier. A sound barrier is inserted between the sound source and the receiving point. The barrier is infinitely long. Sound waves can only be diffracted from above the barrier, and then a sound shadow area is formed, just as light is shaded by an object. In this sound and shadow area, people can feel that the noise is obviously reduced, which is the noise reduction effect of the sound barrier.