Larson Davis 831 - Page 542

Model 831 Manual Glossary D-17
Sound Exposure Level (SEL,
L
E
)
The total sound energy in a specific time period. The
equation for it is
The sound pressure is squared and integrated over a specific
period of time (T
2
-T
1
) this is called the sound exposure and
has the units Pascal squared- seconds or Pascal squared-
hours. P0 is the reference pressure of 20 µPa and T is the
reference time of 1 second. It is then put into logarithmic
form. It is important to note that it is not an average since the
reference time is not the same as the integration time.
Sound Pressure The physical characteristic of sound that can be detected by
microphones. Not all pressure signals detected by a
microphone are sound (e.g., wind noise). It is the amplitude
of the oscillating sound pressure and is measured in Pascals
(Pa), Newtons per square meter, which is a metric equivalent
of pounds per square inch. To measure sound, the oscillating
pressure must be separated from the steady (barometric)
pressure with a detector. The detector takes out the steady
pressure so only the oscillating pressure remains. It then
squares the pressure, takes the time average, and then takes
the square root (this is called rms for root-mean square).
There are several ways this can be done.
SE p
A
2
t
k
td
T
1
T
2

=
SEL 10Log
10
p
2
t td
T
1
T
2

p
0
2
T
-------------------------
=