Sound waves propogate in roughly spherical form through the air and into the interior (air-borne sound). They are reflected to a greater or lesser extent by all the surfaces enclosing the room and by all the objects in the room. The smoother and harder the surface, the less distorted and more complete is the sound.
One strategy to combat air-borne sound transmission is to increase the mass of the components. The object is made as heavy as possible and so given a high inertia i.e., it consists of a material with a high density and therefore air-borne sound waves cause it to vibrate only to a limited extent. Another way of dealing with air-borne transmission is to provide an efficient seal, which prevents the air-borne sound propagating through leakage points such as joints, gaps, and seams. There is also the possibility of attenuating air-borne sound with double-leaf construction with an insulated cavity.
Read more in Facade Construction Manual
, T. Herzog, R. Krippner, and V. Lang, page 24.