HD2010UC
- 123 -
V4.2
Sound Pressure Level with Frequency Weighting:
The sound pressure level can be weighted in
frequency applying a filter that changes in a predetermined way the signal spectral structure. Acous-
tic standard filters are referred to as A and C.
Sound Pressure Level with Time Weighting:
The sound pressure level can be exponentially
weighted over the time with a given time constant. It is defined by the expression:
⋅
⋅
=
∫
∞
−
−
−
t
t
Yp
d
p
e
p
L
ξ
ξ
τ
τ
ξ
2
0
2
10
)
(
1
log
10
where:
τ = time constant expressed in seconds.
Y = symbol associated to the applied time constant.
ξ = fictitious
variable for the integration over elapsed time up to t measurement instant.
p
2
(ξ) = the instantaneous squared pressure.
p
2
0
= the square of reference pressure.
The sound pressure level can be weighted over the time with two standard time constants: FAST (F)
and SLOW (S), corresponding to 0.125s and 1s, respectively. A third time weighting called
IMPULSE (I) has been defined for the identification of impulsive components, presenting a time
constant for increasing levels equal to 35ms, while for decreasing levels it equals 1.5s.
The sound pressure level can be weighted both in frequency and in time. For example, L
AFp
will in-
dicate a frequency weighted level with A filter and with FAST time constant.
Sound Pressure Peak Level:
referred to as L
pk,
it equals the absolute value of the maximum sound
pressure in a given time interval, expressed in decibel. Sound pressure peak level can be frequency
weighted.
Continuous Equivalent Sound Pressure Level:
referred to as L
eq,
it is defined over a T time inter-
val as:
⋅
=
∫
−
t
T
t
T
eq
d
p
p
T
L
ξ
ξ
2
0
2
10
,
)
(
1
log
10
where:
T = t
2
-t
1
is the time interval under examination.
ξ = fictitious variable for the integration over elapsed time up to t measurement instant.
p
2
(ξ) = the instantaneous squared pressure.
p
2
0
= the square of reference pressure.
The equivalent sound pressure level can be frequency weighted. For example, L
Aeq,T
will give the
equivalent sound pressure level over T interval, frequency weighted with A filter.
Summary of Contents for DeltaOHM HD2010UC
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