Larson Davis SoundAdvisor 831C Reference Manual page 238

Criterion Sound Level (L
Daily Personal Noise Exposure (L
Day-Night Average Sound Level (DNL, L
Decibel (dB)
SoundAdvisor Model 831C
)
c
It is the sound level which if continually applied for the Criterion Duration will produce a Noise
Dose of 100%. The current OSHA Criterion Level is 90 dB.
Standard: ANSI S12.19
)
EP,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
)
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
L = 10Log
dn
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 midnight to 7 a.m. have 10 added to them to represent less
tolerance 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.
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 deci-
bel provides us with the possibility of representing a large span of signal levels in a simple manner
as opposed to using the basic unit Pascal for acoustic measurements.
It is not possible to directly add or subtract physical quantities when expressed in decibel form
since the addition of logarithmic values correspond to multiplication of the original quantity.
The word level is normally attached to a physical quantity when expressed in decibels; for exam-
ple, L represents the sound pressure level.
p
The difference between the sound pressure for silence versus loud sounds is a factor of
1,000,000:1 or more, and it is very unpractical to use these large numbers. Therefore, a measure
that would relate to "the number of zeros" would help, for example, 100,000 would be equal to 50
and 1000 would be equal to 30 and so on. This is the basic principal of the dB measure.
= 83 dB.
EP,d
0700

1  
  10 
L + 10

----- -
i
10 +
10
24

0000
2200 2400

   10 
L 10 L + 10
i i
10 + 10
0700 2200



C-3