The Single Event Level SEL

1
The Single Event Level SEL

• Angelo Farina

2
The Equivalent Continuous Level (Leq)
The continuous equivalent level Leq (dB) is
defined as where T is the total measurement
time, p(t) is the instantaneous pressure value
and prif is the reference pressure

• Leq,T ? dB (linear frequency weighting)
• LAeq,T ? dB(A) (A weighting)

3
Definition of SEL (Single Event Level)
the SEL is the equivalent level packed in one
second
4
Definition of SEL (Single Event Level)
the SEL is the equivalent level packed in one
second
5
Example of SEL (Single Event Level)
Time history of the passage of an aircraft
6
Noise from roads and railways

• Angelo Farina

7
Contnuous Line Sources
Many noise sources found outdoors can be
considered line sources roads, railways,
airtracks, etc.

• Geometry for propagation from a line source to a
  receiver
• in this case the total power is dispersed over a
  cylindrical surface

In which Lw is the sound power level per meter
of line source
8
Coherent cylindrical field

• The power is dispersed over an infinitely long,
  pulsating cylinder

L
r
In which Lw is the sound power level per meter
of line source
9
discrete (and incoherent) linear sources
Another common case is when a number of point
sources are located along a line, each emitting
sound mutually incoherent with the others

• Geometry of propagation for a discrete line
  source and a receiver
• We could compute the SPL at the receiver as the
  energetic (incoherent) summation of many
  spherical wavefronts. But at the end the result
  shows that SPL decays with the same cylindrical
  law as with a coherent source

Lw Note that the incoherent SPL is 2
dB louder than the coherent one!
10
A road is a sequence of point sources
d
V (km/h)

• EXAMPLE
• V 50 km/h
• Q 500 vehicles/h
• Lw,1veic 90 dB(A)
• Hence
• d V/Q 50000/500 100 m
• Lw Lw,1vehicle 10log10(d) 90
  10log10(100) 70 dB(A)
• Consequently, at a distance r 50 m, we get
• Lp,50m Lw 10log10(r) 6 70
  10log10(50) 6 47 dB(A)

11
Definition of SEL (Single Event Level)
The SEL is the equivalent level packed in one
second
SEL
Leq
12
Relationship between SEL and Lw
We did find that
SEL is measured at the standard distance r 7.5
m, and referes to just one of the Q vehicles
passing each hour, packed in one second
When V50 km/h, we get SEL Lw 26.19 dB(A)
For a constant value of Lw, SEL decreases with
the speed of vehicles V
13
Computing the time profile
14
Effect of vehicles speed
Sound Power Level Lw increases with speed above
30 km/h
15
Effect of vehicles speed
Aerodynamics
6 dB/radd.
Rolling
Engine
Sound Power Level Lw increases with speed above
30 km/h
16
Time profile vs vehicles speed
Increasing the speed the profile becomes shorter
and higher
17
SEL vs vehicle speed
-3 dB/radd.
3 dB/radd.
SEL has a minimum around 70 km/h
18
SEL vs vehicle speed
SEL has a minimum around 70 km/h
19
Definition of personal exposure level (Lep)
The personal exposure level Lep (dB) is defined
as where 8h is the standardised duration of a
work day. Hence
20
Example of Lep computation