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Octave Bands - Hearing Protection |
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Although there are other methods for assessing the effectiveness of hearing protection for the worker, the most widely used is that of octave analysis. When measuring noise for an assessment of hearing damage/prevention to a worker it is best to use the A weighting filter in conjunction with octave analysis, as it is easier to see which frequencies contribute most significantly to the A weighted Lp.
It is normal for hearing protection manufacturers to quote the octave band attenuation of their devices, typically in the eight octave bands 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz and 8kHz. They may quote the APL (Assumed Hearing Protection Level) for each frequency. The APL is commonly acknowledged to be:
APL = Mean Value - 1 Standard Deviation
For example, the Bilsom 727 hearing defenders have the following data:
|
Frequency (Hz) |
63 |
125 |
250 |
500 |
1K |
2K |
4K |
8K |
|
Mean Value (dB) |
16.8 |
13.9 |
19.9 |
29.7 |
35.8 |
35.9 |
35.9 |
37.4 |
|
Standard Deviation (dB) |
2.9 |
3.3 |
2.9 |
2.9 |
2.9 |
2.2 |
3.9 |
4.4 |
|
Assumed Protection (dB) |
13.9 |
10.6 |
17.0 |
27.0 |
33.0 |
33.8 |
36.1 |
33.1 |
A number of methods can then be used to arrive at a single figure for the assumed protected Lp. |
