Does the sound decay with distance from the source?
When a point source radiates uniformly into free space, the distribution obeys the inverse square law; thus the intensity I can be written as the sound power W divided by (4π r2) where r is the distance between the source and the measuring location.
 

What do sound isolation and insulation mean?
Sound Isolation is separating sound energy from the utility space. This is usually achieved by using proper isolating ‘screens’ or partitions.Insulation: As a noun it means material which insulates. To insulate is to cut off from connection or communication as in to prevent the passing of heat, sound, electricity, etc from a body, or area, to another. Thus, to place in a detached situation. In acoustics, Insulation value is the capacity of a material to prevent noise from reaching a receiver room.