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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