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Unit
Octave Band Levels
Hz
63 125 250 500 1k
2k
4k
8k
Ear muff, mean attenuation
dB
-
13
20
33
35
38
47
41
Standard Deviation
dB
-
6
6
6
6
7
8
8
Assumed protection
dB
-
7
14
27
29
31
39
33
Corrected level
dB
66
80
93
98
98
98
95
92
Levels at ear
dB
66
73
79
71
69
67
56
59
Predicted level of noise with
protection
81 dBA
4dB correction
85 dBA
In accordance with the Control of Noise at Work Regulations 2005, the
predicted level of noise with hearing protection must be increased by 4dB,
therefore the quotable predicted noise level taking into account the worn
hearing protection is 85dBA.
Protection Calculation - HML Method (High Medium Low)
Not as accurate as the octave band method but can be used on instrumentation
that do not have octave band analysis. This method can also be used for noise
at work assessments.
Simply measure the A-weighted and C-weighted energy equivalent sound level
(LAeq and LCeq) simultaneously.
LAeq = 103.2 dBA
LCeq = 103.4 dBC
Take the manufacturers ear protector data: -
H = 25 dB
M = 19 dB
L = 13 dB
Determine (LCeq – LAeq) and then enter the manufacturer’s data into the
relevant equation to find the predicted noise rating PNR: -
If (LCeq – LAeq) <= 2 then :-
PNR
M
H M
−
4
L
Ceq
L
Aeq
−
2
−
(
)
⋅
−
:=
If (LCeq – LAeq) > 2 then :-
PNR
M
M L
−
8
L
Ceq
L
Aeq
−
2
−
(
)
⋅
−
:=
