For an existing acoustic environment, first measure the sound pressure level of each octave background noise, and then overlay the measured noise spectrum curve on the NR graph (coordinate alignment), with the spectrum and NR curve anywhere. The tangent highest NR curve represents the NR number of the background noise of the acoustic environment. When the NR number is used to indicate the noise environment design allowable noise standard, the noise value of each frequency band should not exceed the specified value of the corresponding NR curve for the corresponding frequency band, thereby determining the control value of the noise level of each frequency band.
After determining the NR number, the corresponding octave band sound pressure level can be calculated by formula: LP=a+bNR dBA
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