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Casella CEL-35X dBadge Users Handbook – Page 37

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)

(M-L)

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Casella CEL-352 dBadge Manuale delle Istruzioni Pagina 37

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