Sound intensity measures power density as watts per unit area
Evidence
The sound intensity is defined as the power per unit area. Therefore the sound intensity as a function of distance from a sound source is given by: where I = the sound intensity (in W m−2) Wsource = the power of the source (in W) and r = the distance from the source (in m) Equation 1. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 301
The energy of a sound wave is a measure of the amount of sound present. However, in general, we are more interested in the rate of energy transfer than in the total energy transferred. Therefore we are interested in the amount of energy transferred per unit of time, that is, the number of joules per second (watts) that propagate. Sound is also a three-dimensional quantity, and so a sound wave will occupy space. Because of this, it is helpful to characterize the rate of energy transfer with respect to area, that is, in terms of watts per unit area. This gives a quantity known as the “sound intensity,” which is a measure of the power density of a sound wave propagating in a particular direction, as shown in Figure 1.10. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 176
Categorization
- DEFINE: Clean one-line definition of sound intensity as power per unit area — the fundamental definitional building block for the chapter.
- corroborated: 4 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 301; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 176
- XREF: connects to: Sound intensity measures energy transfer rate per unit area — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 176; Sound power level can be derived by dividing intensity by radiating area; Sound intensity level and sound pressure level are roughly equivalent