Casella CEL CEL-35X dBadge - Manual (Page 41)

Casella CEL-35X dBadge Users Handbook – Page 41
The LC-A value displayed on the CEL-352 dB
adge „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)
Where PNR is the predicted noise level reduction provided by the
hearing protection. For example, if from the CEL-352 dB
adge „Plus‟
the values were:
L
Ceq
102.4dB L
Aeq
98.6dB
Therefore, as the L
Ceq
– L
Aeq
value is greater than 2:
PNR = M
–
x (L
Ceq
– L
Aeq
– 2)
From the example of the hearing protector mentioned above:
PNR = 25
–
x (102.4
– 98.6 – 2)
PNR = 25
– 1 x 1.8
PNR = 25
– 1.8
PNR = 23.2dB
The A-weighted SPL at the ear = L
Aeq
– PNR
The A-weighted SPL at the ear = 98.6
– 23.2 = 75.4 = 75dB(A)*
*Note:
some countries assume that „real world factors‟ will effectively
reduce the effectiveness of hearing protection. For example, in the
UK a further standard 4dB is taken off the PNR, so in this case the
value at the ear would be 79dB(A).
(H-M)
4
(M-L)
8
(25-17)
8
(M-L)
8