2.3.3 Sound Intensity
Sound intensity is the amount of sound power flowing across a particular imaginary
surface with an area of 1m2. It is measured in watts per square metre (Wm−2). Its decibel
counterpart is sound intensity level, and it is measured in some advanced acoustical
investigations.From equation 2.6, it is clear that the sound intensity will decrease with
the square of the distance. The factor A is reduced as obstructions are introduced.
Typically, only half of free field is approached, A is reduced to 2πr2 for hemispherical
radiation. (For l/4 spherical radiation A = πr2; for a spherical radiation A = πr2/2.)
The sound intensity, like sound pressure and sound power, also covers a large range of
values. Sound intensity is expressed as a dB level described by the following relationship
[20–22]:
LI = 10logI/Ir (2.7)
where LI = sound intensity level,dB; I = sound intensity at a given distance, Ir =
reference sound intensity, 10−12W/m2.