
107Mold and Environmental Problems
e energy propagated by a sound wave is a function of its intensity. Conversely, the inten-
sity of the wave is the average power per unit area. e power per unit area of a sound wave
equals the excess pressure times the particle velocity. e intensity over one cycle is given by
I
P
v
=
2
2ρ
(4.12)
where
I is the intensity
P is the pressure amplitude
ρ is the average density of air
v is the velocity of the sound wave
Since the human ear has a large range of intensities over which it responds, a logarithmic scale
is used instead of a linear scale. e intensity levels are then expressed in decibels or dBA where
dBA = 10