Casella CEL-35X dBadge Users Handbook – Page 38
10.3 Using the CEL-352 for the Selection of
Hearing Protection
The CEL-352 dBadge ‘Plus’ can be used for the selection of
hearing protection by 2 different methods. These are the Single
Number Rating (SNR) and the High, Medium, Low (HML) methods.
Hearing protection manufacturers will provide data as follows:
HML values H=31 M=25 L=17
SNR value = 28
The SNR value is a single value which represents the attenuation
of the hearing protection. The Sound Pressure Level (SPL) at the
ear can be calculated as follows:
A-weighted SPL at the ear = L
Ceq
– SNR
For example, if the measured L
Ceq
from the CEL-352 dBadge ‘Plus’
was 102dB, and using the value for SNR in the example above
A-weighted SPL at the ear = 102
– 28 = 74dB(A)
The HML method is a more effective method of calculating the
effectiveness of hearing protection because it takes into account
the frequency component of the noise. This is because the H, M
and L values is the attenuation of the hearing protection at high,
medium and low frequencies respectively.
The LC-A
value displayed on the CEL-352 dBadge ‘Plus’ (see
Figure 21) is the L
Ceq
– L
Aeq
. It is important to know this because
using the HML method requires 2 different formulas depending on
the L
Ceq
– L
Aeq
value, as shown below:
If L
Ceq
– L
Aeq
is less than or equal to 2:
PNR = M – x (L
Ceq
– L
Aeq
– 2)
If L
Ceq
– L
Aeq
is greater than 2:
PNR = M – x (L
Ceq
– L
Aeq
– 2)
(H-M)
4
(M-L)
8
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