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The Single Event Level SEL

The Single Event Level SEL

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The Single Event Level SEL

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  1. Dip. di Ingegneria Industriale - Università di Parma Parco Area delle Scienze 181/A, 43100 Parma – Italy angelo.farina@unipr.it The Single Event Level SEL Angelo Farina Single Event Level - SEL

  2. The Equivalent Continuous Level (Leq): The continuous equivalent levelLeq (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) Single Event Level - SEL

  3. Definition of SEL (Single Event Level) the SEL is the equivalent level packed in one second Single Event Level - SEL

  4. SEL 1s Definition of SEL (Single Event Level) the SEL is the equivalent level packed in one second Single Event Level - SEL

  5. Example of SEL (Single Event Level) Time history of the passage of an aircraft Single Event Level - SEL

  6. Dip. di Ingegneria Industriale - Università di Parma Parco Area delle Scienze 181/A, 43100 Parma – Italy angelo.farina@unipr.it Noise from roads and railways Angelo Farina Single Event Level - SEL

  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 Single Event Level - SEL

  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 Single Event Level - SEL

  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! Single Event Level - SEL

  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 – 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) Single Event Level - SEL

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

  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 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 Single Event Level - SEL

  13. Computing the time profile Single Event Level - SEL

  14. Effect of vehicle’s speed Sound Power Level Lw increases with speed above 30 km/h Single Event Level - SEL

  15. Effect of vehicle’s speed Aerodynamics 6 dB/radd. Rolling Engine Sound Power Level Lw increases with speed above 30 km/h Single Event Level - SEL

  16. Time profile vs vehicle’s speed Increasing the speed the profile becomes shorter and higher Single Event Level - SEL

  17. SEL vs vehicle’ speed -3 dB/radd. 3 dB/radd. SEL has a minimum around 70 km/h Single Event Level - SEL

  18. SEL vs vehicle’ speed SEL has a minimum around 70 km/h Single Event Level - SEL

  19. Lep 8h Definition of personal exposure level (Lep): The personal exposure levelLep (dB) is defined as: where 8h is the standardised duration of a work day. Hence: Single Event Level - SEL

  20. 84 80 78 75 75 75 1h 1h 2h 3h 1h 2h Example of Lep computation: Single Event Level - SEL