C-16
Model 820 Technical Reference Manual
where p
0
is the reference sound pressure of 20 µPa. The square of
the sound pressure is a power-like quantity that can be expressed in
the original form of the level definition
Sound Pressure Level can be converted to sound pressure as fol-
lows. If the sound pressure is 1 Pascal, then the sound pressure
level is
Calibrators often use a level of 94 dB so they generate a sound
pressure of 1 Pascal.
If the sound pressure level = 76.3 dB, then the sound pressure is
Energy Average (L
eq
)
: The value of a steady sound measured over
a fixed time period that has the same sound energy as the actual
time varying sound over the same period. This descriptor is widely
used. It is a fixed average (See Sound Pressure).
Impulse
: The value of an impulsive sound. The reading will depend
on the time-weighting applied.
Unweighted Peak
: The peak value of a sound with a meter that has
flat frequency weighting and a peak detector.
L
p
20log
10
p
rms
p
0
----------
=
p
rms
p
0
10
L
p
20
⁄
=
L
p
10log
10
p
rms
2
p
0
2
----------
=
p
rms
2
p
0
2
10
L
p
10
⁄
=
L
p
20log
10
1
20 10
6
–
•
----------------------
20log
10
50000
[
]
20 4.699
[
]
94.0
dB
=
=
=
=
Pa
20 10
6
–
•
10
76.3 20
⁄
•
20 10
3.815 6
–
•
20 10
2.185
–
•
20 0.0065
[
]
0.13
=
=
=
=
=
