Instruction Manual
Sound Level Meter Types 2245 –
Instruction Manual
Page 33 of 110
Peak Sound Level
The peak sound level,
L
xpeak
(T)
, is defined as twenty times the logarithm to base ten of
the ratio of the greatest absolute instantaneous sound pressure,
p
x
(t)
, within a time
interval starting at
t
=
T
and ending at
t
=
T
+Δ
t
, to the reference sound pressure,
p
0
,
instantaneous sound pressure being obtained with a frequency weighting,
x
, where:
x
is A for A-weighted, B for B-weighted, C for C-weighted or Z for Z-weighted
p
x
(t)
is the x frequency-weighted instantaneous sound pressure
p
0
is the reference sound pressure, equal to 20 μPa
T
is the start time of the measurement, indicated as
Start Time
Δ
t
is the measuring period, indicated as
Elapsed Time
The maximum peak sound level is expressed in decibels (dB).
The symbols used by the sound level meter for peak sound levels are (for A, B, C and Z
frequency weighting):
L
Apeak
,
L
Bpeak
,
L
Cpeak
,
L
Zpeak
Average Sound Level
Average Sound Level with Time Weighting S and Exchange Rate Q = 4 or 5. Exchange
rate is the increase in noise level that corresponds to a doubling of the noise level. This
is a widely used occupational health noise parameter in the USA, corresponding to the
LAeq used otherwise.
The symbols used by the sound level meter for average sound levels are (for exchange
rates 4 and 5):
L
avS4
,
L
avS5
Statistics
Statistics can be based on sampling the continuous output of the A-weighted
exponential detectors F every 16 ms or S every 125 ms or the 1 s linearly averaged
results
L
Aeq
. The samples are divided into 0.2 dB classes in which the frequency of
appearance is counted. Based on the counted frequency distribution the percentile
sound levels (also called the exceedance levels)
L
AyN
are calculated.
x
is A for A-weighted or B for B-weighted
y
is F for Fast-weighted or S for Slow-weighted and nothing for Leq
N
is a percentage between 0.1 and 99.9. It notes the percentage of time that the
indicated noise level was exceeded during the measurement period.