Larson Davis System 824, Reference Manual

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11/3/00 D -3
where q is the Exchange Rate Factor. See Exchange Rate.
Standard: ANSI S1.25
Criterion Sound Level (L
c
)
It is the sound level which if continually applied for the Cri-
terion Duration will produce a Noise Dose of 100%. The
current OSHA Criterion Level is 90 dB.
Standard: ANSI S12.19
Daily Personal Noise Exposure
(
LEP,d
)
It is the level of a constant sound over the Criterion Duration
that contains the same sound energy as the actual, unsteady
sound over a specific period. The period is generally shorter,
so the sound energy is spread out over the Criterion Duration
period.
Example: If the Criterion Duration = 8 hours and the specific
period is 4 hours and the average level during the 4 hours is
86 dB, then the L
EP,d
= 83 dB.
Day-Night Average Sound
Level (DNL, L
dn
)
A rating of community noise exposure to all sources of
sound that differentiates between daytime and nighttime
noise exposure. The equation for it is
The continuous equivalent sound level (See definition) is
generally calculated on an hourly basis and is shown in the
equation as L. The values for the hourly periods from mid-
night to 7 a.m. have 10 added to them to represent less toler-
ance for noise during sleeping hours. The same occurs from
10 p.m. to midnight. They are energy summed and converted
to an average noise exposure rating.
Decibel (dB) A logarithmic form of any measured physical quantity and
commonly used in the measurement of sound and vibration.
Whenever the word level is used, this logarithmic form is
implied. The decibel provides us with the possibilty of rep-
resenting a large span of signal levels in a simple manner as
CSE T
c
10
L
c
q
⁄
=
L
dn
10Log
10
10
L
i
10 +
( )
10
⁄
0000
0700
∑
10
L
i
10
⁄
0700
2200
∑
10
L
i
10 +
( )
10
⁄
2200
2400
∑
+ + =