Airborne sound travels through the air and can be transmitted through an obstruction. When sound reaches an environment where it is unwanted, it becomes noise. Noise can come from both external and internal sources. Traffic noise is an example of an external noise source that can be transmitted through an exterior structure. Noise can also transfer from one room within a building to another by transmitting through an interior partition. Airborne sound can also pass under doorways, through ventilation, over, under, and around obstructions. close window