Quest Engineering The EDGE eg5, User Manual

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Appendix B
Warranty
053-669, Rev A eg5
72
R
el
a
ti
v
e
R
es
p
o
n
se
(
d
B
)
Frequency (Hz)
C-A
The C-A measurement is an L
AVG
that enhances the low- frequency components of the
sound signal. It is the result of subtracting an A-weighted L
AVG
from a simultaneously
collected C-weighted L
AVG
and is sometimes used as the NRR (noise reduction rating)
factor to determine if hearing protection devices are adequate for usage in the field.
Figure B-1: C-A weighting response curve
Combining Noise sources
Because sound levels are measured in decibels they cannot be simply added together. A sound level of
90dB plus 90dB does not yield 180dB but rather 93dB. The procedure for mathematically determining
a combined level of sound from independent measurements made for two noise sources is given
below.
1. Make independent measurements for both noise sources, where each exists without the
presence of the other.
2. Determine the decibel difference between these two measurements.
3. Find that difference on the x-axis of the figure below.
4. Find the point on the curve directly above this difference.
5. Read the corresponding value on the y-axis for that point (the Amount to Add).
6. Add this value to the larger of the two measurements.
Example: Independent measurements for the two noise sources yielded levels of 90 dB and
91 dB. For a difference of 1 dB, the correction factor taken from the curve below
is 2.5 dB.
Therefore the combined level when these two sound sources are present in the measurement
area at the same time 93.5 dB.