Larson Davis System 824, Reference Manual

Page: 523 / 536

11/3/00 D -19
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
follows. 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 pres-
sure 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.
Weighted Peak: The peak value of a sound with a meter that
has a frequency weighting other than flat and a peak detec-
tor.
Sound Power(W)
The sound power emitted by a sound source. It is measured
in Watts.
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
[ ]
94.0dB = = = =
Pa 20 10
6 –
•
10
76.3 20
⁄
•
20 10
3.815 6 –
•
20 10
2.185 –
•
20 0.0065
[ ]
0.13 = = = = =