Abatement and Distance from Source

The disruption of sound pressures waves which reduces the noise is called attenuation

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Spherical Distance

sound pressure in distance from source

The sound pressure in a spherical distance from a source can be expressed as:

p2 = ρ c N / (4 π r2) (1)

where

p = sound pressure (Pa, N/m2)

ρ = density of air (kg/m3)

c = speed of sound (m/s)

N = sound power (W)

π = 3.14

r = distance from source (m)

Half Spherical Distance

sound pressure in distance from source

The sound pressure in a half spherical distance from a source can be expressed as:

p2 = ρ c N / (4 π r2 / 2) = 2 ρ c N / (4 π r2) (2)

A generic expression can be formulated as:

p2 = D ρ c N / (4 π r2) (3)

where

D = directivity coefficient

The directivity coefficient depends on several parameters - the position and direction of the source, the room or the surrounding area, etc.

The Sound Pressure Level - Lp - can be expressed as:

Lp = 20 log ( p / pref ) = 20 log ( (D ρ c N / (4 π r2))1/2 / pref )

= 20 log ( 1/r (D ρ c N / (4 π))1/2 / pref ) (4)

where

pref = 2 10-5 - reference sound pressure (Pa)

Note! For every doubling of the distance from the noise source, the sound pressure levels - Lp, will be reduced by 6 decibels.

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Related Topics

  • Acoustics Room acoustics, acoustic properties - decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity, attenuation ..

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