Text: [Acoustics] Under far field/free field conditions, sound intensity varies inversely with the square of the distance from the source. The difference in sound pressure level between far field locations is expressed as: Lp2 = Lp1 - 20 log(R2/R1) where: Lp1 = sound pressure level in decibels at location 1 Lp2 = sound pressure level in decibels at location 2 R1 = distance from noise source to point 1 R2 = distance from noise source to point 2 (R1 and R2 must have the same units)

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