ABSTRACT
Noise control can be achieved by preventing the generation and spreading of noise. In this chapter, outdoor sound propagation and the effects of noise barriers are discussed.
A. Attenuation due to distance
a. Attenuation due to distance from a point source
The sound intensity I at a distance d generated from a point sound source whose acoustic power W in a free field is given by
I= W 4πd2
(5.1)
since the total energy that passes through a sphere of surface area 4πd2 is W. Thus, I is inversely proportional to the square of the distance. The sound
intensity/pressure level at this point can be expressed as follows
L=LW −10 log10 4π −10 log10 d2 =LW −11−20 log10 d (dB)
(5.2)
where the sound power level of the source LW is 10 log10(W/10 −12).
