Spartan 821/721 Manual Glossary C-3
Daily Personal Noise Exposure (L
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
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 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.
Decibel (dB)
A unit of measure commonly used to describe the ratio of one power level or field level
value to another on a logarithmic scale. The decibel is a simplified way of representing a
large span of signal levels, and sometimes very large numbers, as opposed to using the
Pascal. For example:
To directly add or subtract physical quantities expressed in decibel form, you can use
the following equation to convert decibels to Pascals.
With regard to measuring noise exposure, remember the following rules when dB values
are used for sound levels:
• Doubling of the Sound Pressure = 6 dB
L
DN
10Log
10
1
24
------
10
L
i
10+ 10
0000
0700
10
L
i
10
0700
2200
10
L
i
10+ 10
2200
2400
+ +
=
dB Power Ratio
Amplitude
Ratio
50 100 000 316.2
3 3.995 ≈ 4 1.995 ≈ 2
-50 0.000 01 0.003 162
dB 10Log
10
P
2
P
0
2
--------
20Log
10
P
P
0
-----
;= =
p
0
20Pa=
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