Appendix I:A-4. A-Weighted Network
The A-weighted network has become popular in the assessment of overall noise hazard because it is thought to provide a rating that indicates the injurious effects of noise on human hearing.
• The A-weighted sound level has been adopted as the measurement for assessing noise exposure by OSHA and the American Conference of Governmental Industrial Hygienists (ACGIH).
• The A-weighted sound levels have also been shown to provide reasonably good assessments of speech interference and community disturbance conditions, and have been adopted by the Environmental Protection Agency (EPA) for such purposes.
A graphical representation of the A-weighted network of sound level meters is shown below with the octave-band correction factors indicated.

Calculating the Equivalent A-Weighted Sound Level

There are occasions when it is necessary to convert a set of octave band sound pressure levels into an equivalent A-weighted sound level. This is easily done by applying the A-scale correction factors for the nine standard octave center frequencies and combining the corrected values by decibel addition. The A-scale correction factors are the values of the A-weighting network at the center of each particular octave band. The resulting value is designated the A-weighted sound level (dBA).
Example:
 Octave Band Center Frequency (Hz) Example Lp A-Scale Correction Factor (dB) Corrected Values (dB) 31.5 94 -39 55 63 95 -26 69 125 92 -16 76 250 95 -9 86 500 97 -3 94 1,000 97 0 97 2,000 102 +1 103 4,000 97 +1 98 8,000 92 -1 91
The A-weighted sound level can now be calculated by combining the corrected band levels:
LA = 10 log10 (S 10Li/10) LA = 10 log (105.5 + 106.9 + 107.6 + 108.6 + 109.4 + 109.7 + 1010.3 + 109.8 + 109.1) = 105 dBA

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