Sound intensity is energy flow per unit area, spanning a trillion-to-one range

Evidence

The sound intensity represents the flow of energy through a unit area. In other words, it represents the watts per unit area from a sound source, and this means that it can be related to the sound power level by dividing it by the radiating area of the sound source. … The sound intensity of real sound sources can vary over a range, which is greater than one million-million (1012) to one. Because of this, and because of the way we perceive the loudness of a sound, the sound intensity level is usually expressed on a logarithmic scale. This scale is based on the ratio of the actual power density to a reference intensity of 1 picowatt per square meter (10−12 W m−2). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 177

Categorization

• DEFINE: Defines sound intensity as watts per unit area and grounds the reference intensity for the SIL scale.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 177