Instruction manual

118
Technical Notes
L
AE
(sound exposure level)
The L
AE
(sound exposure level) is a hypothetical constant 1-second sound pressure level
having the same energy as a single-event sound pressure level measured with A weight-
ing. It is determined by the following equation.
t
1
: Measurement start time
t
2
: Measurement end time
T0: Reference time (1 second)
p0: Reference sound pressure 20 µPa (2 × 10
-5
N / m
2
)
pA(t): Instantaneous sound pressure measured with sound pres-
sure level meter A weighting
Expressing the above equation for sound pressure level yields the following.
L
A(t)
: Instantaneous sound pressure level
In the sound pressure level meter NA-27, this statement is used as reference, and digital
processing is carried out according to the following equation.
N0: Number of samples per second
In the NA-27, the sampling interval for A/D conversion is 10 ms (100 samples per sec-
ond), and L
AE
processing is carried out every interval. The L
AE
reading can therefore be
displayed already during measurement.
L
x
(percentile sound pressure level)
The L
x
(percentile sound pressure level) is the sound pressure level which was exceeded
for x percent of the measurement time. The NA-27 allows the user to select five values for
x (from 1 to 99, in 1-percent steps), and calculates the time percentile level for these five
values simultaneously. The sampling interval for L
x
processing is 100 ms (10 samples per