How do sound waves travel through walls?

Unlike light, which is reflected from an opaque wall and cannot travel through, some of the sound waves are not reflected but continue to move through the wall, causing the wall to vibrate and transmit the sound. However, what is inside the cavity of the wall can affect how much sound travels through to the other side of the wall; if the wall is fairly solid, there is little to disperse the sound waves and some of the sound will make it through. If the cavity contains cords, insulation batting, etc., the sound waves are more likely to be scattered, which can mean that little or no sound gets through to the other side. Hence, a soundproofed wall won’t let the sound waves pass through.