This document specifies methods for qualifying an environment that approximates to an acoustic free field near one or more reflecting planes. The goal of the qualification is to determine the environmental correction , which is used to correct for reflected sound when determining the sound power level or sound energy level of a noise source from sound pressure levels measured on a surface enveloping the noise source (machinery or equipment) in such an environment.
In practice, the  value determined will be a function of both the reflected sound from the test environment and the shape and size of the measurement surface used for the  determination. For the purposes of this document and the documents that refer to it, the differences between  values determined with different measurement surfaces are assumed to be included in the stated measurement uncertainty for the test method.