Instruction Manual
Sound Level Meter Types 2245 –
Instruction Manual
Page 31 of 110
Equivalent Continuous Sound Level
The equivalent continuous sound level (also called time-average sound level),
L
xeq
(T)
, is
defined as twenty times the logarithm to base ten of the ratio of a root-mean-square
sound pressure during a time interval to the reference sound pressure, sound pressure
being obtained with a frequency weighting, x. The time interval is starting at
t
=
T
and
ending at
t
=
T
+ Δ
t
where:
x
is A for A-weighted, B for B-weighted, C for C-weighted or Z for Z-weighted
T
is the start time of the measurement, indicated as
Start Time
Δ
t
is the averaging time interval, indicated as
Elapsed Time
The equivalent continuous sound level is expressed in decibels (dB). In symbols,
equivalent continuous sound level,
L
xeq
(T)
, is given by:
where:
ξ is a dummy variable of time integration over the averaging time interval
p
x
(ξ) is the x frequency-weighted instantaneous sound pressure
p
0
is the reference sound pressure, equal to 20 μPa
The symbols used by the sound level meter for equivalent continuous sound
levels are (for A, B, C and Z frequency weighting):
L
Aeq
,
L
Beq
,
L
Ceq
,
L
Zeq
Equivalent Continuous I-weighted Sound Level
The equivalent continuous I-weighted sound level (also called average I-weighted
sound level),
L
xIeq
(T)
, is defined as ten times the logarithm to base ten of the mean of
ten to the power of the I time-weighted sound level,
L
xI
(t)
, divided by ten during a time
interval. The time interval is starting at
t
=
T
and ending at
t
=
T
+ Δ
t
where:
x
is A for A-weighted, B for B-weighted, C for C-weighted or Z for Z-weighted
T
is the start time of the measurement, indicated as
Start Time
Δ
t
is the averaging time interval, indicated as
Elapsed Time
The equivalent continuous I-weighted sound level is expressed in decibels (dB). In
symbols, equivalent continuous I-weighted sound level,
L
xIeq
(T)
, is given by:
where ξ is a dummy variable of time integration over the averaging time interval
The symbols used by the sound level meter for equivalent continuous I-weighted sound
levels are (for A, B, C and Z frequency weighting):
L
AIeq
,
L
BIeq
,
L
CIeq
,
L
ZIeq