Environmental Noise

1. Environmental Noise Architectural Acoustics II March 17, 2008

2. Outline • Barriers • Basic insertion loss • Location relative to S and R • Edge geometry • Source and receiver conditions • Close vs. far • Moving vs. stationary • Distance effects • Ground cover • Grazing incidence • Temperature inversions • Traffic and railroad noise

3. Sources/Resources • Long, Architectural Acoustics • J. Foreman, Sound Analysis and Noise Control, Van Nostrand Reinhold, 1990. • Kurze and Anderson, “Sound Attenuation by Barriers,” Appl. Acoust. 4, 35 (1971). • S. Ho et al., “Noise reduction by a barrier having a random edge profile,” JASA 101 (5) 1997. • Z. Maekawa, ‘‘Noise reduction by screens,’’ Appl. Acoust. 1, 157, 1968. • D. N. May and N. M. Osman, “Highway noise barriers: new shapes,” J. Sound. Vib. 73 (1), 1980. • Berkhoff, “Control strategies for active noise barriers using near-field error sensing,” JASA 118 (3), 2005.

4. Noise Barrier Performance http://www.ashraeregion7.org/tc26/pastprograms/Outdoor_Noise/barriers.pdf

5. -2π -π 0 π 2π Math Review • Hyperbolic tangent:

6. b a R d θ S = source S R = source d = source-to-receiver distance a + b = shortest path from S to R over the barrier θ = angle between and the Fresnel Number: barrier normal Barrier Geometry Barrier Kurze and Anderson, “Sound Attenuation by Barriers,” Appl. Acoust. 4, 35 (1971).

7. Barrier Insertion Loss • Assumptions • S is a point source • No sound is transmitted through the barrier • The barrier is infinitely long • Ground reflections and other secondary propagation paths are negligible Kurze and Anderson, “Sound Attenuation by Barriers,” Appl. Acoust. 4, 35 (1971).

8. Theoretical Barrier Performance for a Point Source What does the increasing trend with N suggest about the optimal placement of a barrier given the source and receiver positions?

9. Theoretical Barrier Performance for a Line Source • Integrate the point-source IL equation R Barrier Line Source

10. Comparison of Point Source and Line Source IL Foreman, Sound Analysis and Noise Control, Figure 4.28, p. 104.

11. Comparison with Measurements Ho et al., “Noise reduction by a barrier having a random edge profile,” JASA 101 (5) 1997.

12. Homework Assignment • Come up with a new barrier design • Explain why you think it will out-perform a standard barrier • Due Thursday 3/27

13. Jagged-Edge Barriers “…the edge [at the top of a noise barrier] acts as a line source. For the traditional straight-edge barrier, the line source is coherent. Since a crooked line source is less coherent, we propose to improve barrier performance by making the edge randomly jagged.” Ho et al., “Noise reduction by a barrier having a random edge profile,” JASA 101 (5) 1997.

14. Jagged-Edge Barriers Improved performance at high frequencies, worse at low frequencies. Why? Ho et al., “Noise reduction by a barrier having a random edge profile,” JASA 101 (5) 1997.

15. Other Barrier Designs 5 5 3.5 2 X Reported broadband increase in IL (dBA) over a straight-edge barrier D. N. May and N. M. Osman, “Highway noise barriers: new shapes,” J. Sound. Vib. 73 (1), 1980.

16. Other Barrier Designs 2.5 X Reported broadband increase in IL (dBA) over a straight-edge barrier D. N. May and N. M. Osman, “Highway noise barriers: new shapes,” J. Sound. Vib. 73 (1), 1980.

17. Other Barrier Designs And THNAD is for ThnadnersAnd oh, are they sad, oh!The big one, you see, has the smaller one's shadow.The shadow the small Thnadner has should be his.I don't understand it, but that's how it is.A terrible mix-up in shadows! Gee-Whizz!

18. Absorptive Barrier Surfaces Long, Architectural Acoustics, Figure 5.9, p. 167

19. Absorptive Barrier Surfaces Long, Architectural Acoustics, Figure 5.10, p. 168

20. Active Barriers: Theory Berkhoff, “Control strategies for active noise barriers using near-field error sensing,” JASA 118 (3), 2005.

21. Microphone Array Sources Barrier Active Barriers: Experiment Berkhoff, “Control strategies for active noise barriers using near-field error sensing,” JASA 118 (3), 2005.

22. Active Barriers: Simulation Results Berkhoff, “Control strategies for active noise barriers using near-field error sensing,” JASA 118 (3), 2005.

23. Environmental Effects • Air absorption due to • Viscosity • Thermal conductivity • Molecular relaxation Sources of energy loss

24. Environmental Effects • Air absorption

25. Environmental Effects • Excess attenuation in forests • f = frequency • r = distance through the forest • Grazing attenuation • Reflection of sound from a soft surface at shallow angles (close to parallel incidence) often results in a phase shift • The reflection destructively interferes with the direct sound to cause excess attenuation • This also occurs in concert halls with grazing incidence sound over audience seats. The attenuation is known as “seat dip”.

26. Environmental Effects Wind velocity increases upward Long, Architectural Acoustics, Figures 5.20 and 5.21, p. 178

27. Truck Noise Long, Architectural Acoustics, Figures 5.28, p. 189

28. Truck Noise Long, Architectural Acoustics, Figures 5.29, p. 190

29. Car Noise Long, Architectural Acoustics, Figures 5.30, p. 190

30. Train Noise Long, Architectural Acoustics, Figures 5.32, p. 191

31. Train Noise Long, Architectural Acoustics, Figures 5.36, p. 195

32. Train Noise Long, Architectural Acoustics, Figures 5.37, p. 195

33. Aircraft Noise