30/11/2012single event level - sel1 the single event level sel angelo farina dip. di ingegneria...

30/11/2012 Single Event Level - SEL 1

The Single Event Level The Single Event Level SELSEL

Angelo Farina

Dip. di Ingegneria Industriale - Università di Parma

Parco Area delle Scienze 181/A, 43100 Parma – Italy

[email protected]


The Equivalent Continuous Level (LThe Equivalent Continuous Level (Leqeq):):

T

rifTeq dt

p

tp

TL

02

2

,

)(1log10

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)


Definition of SEL (Single Event Level)Definition of SEL (Single Event Level)

sTT

TLeqSEL 1log10 0

010

the SEL is the equivalent level packed in one second



the SEL is the equivalent level packed in one second

SEL

1s


Example of SEL (Single Event Level)Example of SEL (Single Event Level)

Time history of the passage of an aircraft

45

55

65

75

85

95 L

ive

llo

So

no

ro in

dB

(A)

0 10 20 30 40 50 Tempo (s)

Fokker 50 - Esponenziale - FAST


Noise from roads and railwaysNoise from roads and railways

Angelo Farina

Dip. di Ingegneria Industriale - Università di Parma

Parco Area delle Scienze 181/A, 43100 Parma – Italy

[email protected]


Contnuous Line SourcesContnuous Line SourcesMany 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:

d

R

r

dx XO

)(8log10

)(6log10

emissioncoherentdLL

emissionincoherentdLL

Wp

Wp

In which Lw’ is the sound power level per meter of line source

dx

r

WI

24

'


Coherent cylindrical fieldCoherent cylindrical field

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

rlg108'LL

rlg102lg10WL

Wlg10

W

W

ILr2

W

lg10I

Lr2W

lg10I

Ilg10L

Lr2

W

S

WI

WI

oo

o

oooI

r

L

In which Lw’ is the sound power level per meter of line source


““discretediscrete”” (and incoherent) linear sources (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!

d

R

1

r 1 r i

S r i-1

i

a

]dB[6dlog10alog10LL Wpp


A road is a sequence of point sourcesA 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 – 10·log10(d) = 90 – 10·log10(100) = 70 dB(A)

Consequently, at a distance r = 50 m, we get:

• Lp,50m = Lw’ – 10·log10(r) – 6 = 70 – 10·log10(50) – 6 = 47 dB(A)



sTT

TLeqSEL 1log10 0

010

The SEL is the equivalent level packed in one second

45

55

65

75

85

95

Liv

ello

So

no

ro in

dB

(A)

0 10 20 30 40 50 Tempo (s)

Fokker 50 - Esponenziale - FAST

Leq

SEL


Relationship between SEL and Lw’Relationship between SEL and Lw’

6log101000

log10 10101.

r

V

QLLeq vehicleW

3600log1065.7log101000

1log10 101010

VLwSEL

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:

19.9log10 10 VLwSEL

When V=50 km/h, we get:

SEL = Lw – 26.19 dB(A)For a constant value of Lw, SEL decreases

with the speed of vehicles V


Computing the time profileComputing the time profile

r

R

r’(x)

x O

Lw

v (m/s)

v·t

11log10)(

11'log10)(22

10

210

tvrLwtLp

trLwtLp

Profilo Temporale - Lw = 90 dB, r = 50 m

10

15

20

25

30

35

40

45

50

-120 -90 -60 -30 0 30 60 90 120

Tempo (s)

Lp

(d

BA

)30


Effect of vehicle’s speedEffect of vehicle’s speed

Sound Power Level Lw increases with speed above 30 km/h

Emissione sonora vs. velocita'

88

90

92

94

96

98

100

102

0 50 100 150 200

Velocita' (km/h)

Lw

(d

BA

)


Effect of vehicle’s speedEffect of vehicle’s speed

Sound Power Level Lw increases with speed above 30 km/h

Emissione sonora vs. velocita'

89

90

91

92

93

94

95

10 100

Velocita' (km/h)

Lw

(d

BA

)

20 30 40 50 60 70 80

6 dB

/radd

.

Engine

Rolling

Aerodynamics


Time profile vs vehicle’s speedTime profile vs vehicle’s speed

Increasing the speed the profile becomes shorter and higher

Profilo Temporale

20

25

30

35

40

45

50

-120 -90 -60 -30 0 30 60 90 120

Tempo (s)

Lp

(d

BA

) 30

50

70


Immissione sonora vs. velocita'

55

56

57

58

59

60

61

62

63

64

65

10 100

Velocita' (km/h)

SE

L (

dB

A)

a 50

m

20 30 40 50 60 70 80

SEL vs vehicle’ speedSEL vs vehicle’ speed

SEL has a minimum around 70 km/h

3 dB/radd.

-3 dB/radd.


SEL vs vehicle’ speedSEL vs vehicle’ speed

SEL has a minimum around 70 km/h

Immissione sonora vs. velocita'

55

56

57

58

59

60

61

62

63

64

65

0 50 100 150 200

Velocita' (km/h)

SE

L (

dB

A)

a 50

m


Definition of personal exposure level (LDefinition of personal exposure level (Lepep):):

T

02rif

2

ep dtp

)t(p

h8

1log10L

The personal exposure level Lep (dB) is defined as:

where 8h is the standardised duration of a work day. Hence:

8h

Lep

h

TLL eqep 8

log10


Example of LExample of Lepep computation: computation:

1h 1h 2h 3h 1h 2h

7580

75

84

7578

dBh

L

dBh

L

ep

eq

4.818

102101103102101101log10

4.8010

102101103102101101log10

8.75.74.85.70.85.7

8.75.74.85.70.85.7

30/11/2012single event level - sel1 the single event level sel angelo farina dip. di ingegneria...

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