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139
Appendix B
Exceedance Level (Ln)
Exceedance levels represent the percent of the run time that was spent at or above the
corresponding dB level.
Example: An L40 equal to 73 dB would mean that for 40% of the run time, the
decibel lever was equal to or higher than 73 dB.
Exceedance levels can be set from 1% to 99%.
Exchange Rate (ER)
Also known as the Doubling Rate, this refers to how the sound energy is averaged over time.
Using the decibel scale, every time the sound energy doubles, the measured level increases
by 3 dB. This is the 3 dB Exchange Rate that most of the world uses. For every increase of 3
dB in the time weighted average, the measured dose would double.
Some organizations such as OSHA in the U.S. have argued that the human ear self
compensates for changing noise levels and they felt that the 3 dB Exchange Rate should be
changed to more closely match the response of the human ear. OSHA currently uses a 5 dB
Exchange Rate which would mean that the reported dose would double with every 5 dB
increase in the time weighted average. The Exchange Rate affects the integrated reading
L
, Dose, and TWA but does not affect the instantaneous sound level.
AVG
ExpHrs
Hours of sound exposure. Accumulated exposure to sound measured in hours using an
Exchange Rate of 3 dB. The display will switch to ExpSec if RTIME is less than one hour.
(
L
[
EXP
=
2
Hrs
ExpSec
Seconds of sound exposure. Accumulated exposure to sound measured in seconds using an
) 3.01
⁄
–
94
] RTIME
eq
------------------- - Pa
3600
OR
2
H
Models SE and DL
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