30/11/2012Single Event Level - SEL1 The Single Event Level SEL Angelo Farina Dip. di Ingegneria Industriale - Università di Parma Parco Area delle Scienze 181/A, Parma – Italy

30/11/2012Single Event Level - SEL2 The Equivalent Continuous Level (L eq ): The continuous equivalent level Leq (dB) is defined as: where T is the total measurement time, p(t) is the instantaneous pressure value and p rif is the reference pressure L eq,T dB (linear frequency weighting) L Aeq,T dB(A) (A weighting)

30/11/2012Single Event Level - SEL3 Definition of SEL (Single Event Level) the SEL is the equivalent level packed in one second

30/11/2012Single Event Level - SEL4 Definition of SEL (Single Event Level) the SEL is the equivalent level packed in one second SEL 1s

30/11/2012Single Event Level - SEL5 Example of SEL (Single Event Level) Time history of the passage of an aircraft

30/11/2012Single Event Level - SEL6 Noise from roads and railways Angelo Farina Dip. di Ingegneria Industriale - Università di Parma Parco Area delle Scienze 181/A, Parma – Italy

30/11/2012Single Event Level - SEL7 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

30/11/2012Single Event Level - SEL8 Coherent cylindrical field The power is dispersed over an infinitely long, pulsating cylinder: r L In which Lw is the sound power level per meter of line source

30/11/2012Single Event Level - SEL9 discrete (and incoherent) linear sourcesdiscrete (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!

30/11/2012Single Event Level - SEL10 A road is a sequence of point sources d V (km/h) EXAMPLE: V = 50 km/h Q = 500 vehicles/h L w,1veic = 90 dB(A) Hence: d = V/Q = 50000/500 = 100 m L w = L w,1vehicle – 10·log 10 (d) = 90 – 10·log 10 (100) = 70 dB(A) Consequently, at a distance r = 50 m, we get: L p,50m = L w – 10·log 10 (r) – 6 = 70 – 10·log 10 (50) – 6 = 47 dB(A)

30/11/2012Single Event Level - SEL11 Definition of SEL (Single Event Level) The SEL is the equivalent level packed in one second Leq SEL

30/11/2012Single Event Level - SEL12 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 V=50 km/h, we get: SEL = Lw – dB(A) For a constant value of Lw, SEL decreases with the speed of vehicles V

30/11/2012Single Event Level - SEL13 Computing the time profile

30/11/2012Single Event Level - SEL14 Effect of vehicles speed Sound Power Level Lw increases with speed above 30 km/h

30/11/2012Single Event Level - SEL15 Effect of vehicles speed Sound Power Level Lw increases with speed above 30 km/h 6 dB/radd. Engine Rolling Aerodynamics

30/11/2012Single Event Level - SEL16 Time profile vs vehicles speed Increasing the speed the profile becomes shorter and higher

30/11/2012Single Event Level - SEL17 SEL vs vehicle speed SEL has a minimum around 70 km/h 3 dB/radd. -3 dB/radd.

30/11/2012Single Event Level - SEL18 SEL vs vehicle speed SEL has a minimum around 70 km/h

30/11/2012Single Event Level - SEL19 Definition of personal exposure level (L ep ): The personal exposure level Lep (dB) is defined as: where 8h is the standardised duration of a work day. Hence: 8h Lep

30/11/2012Single Event Level - SEL20 Example of L ep computation: 1h 2h 3h1h 2h