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From page 305...
... C-3 C H A P T E R C - 1 Introduction to Appendix C This appendix compares the results of the Phase 1 noise measurements at sound-reflecting barriers with the Phase 2 noise measurements at sound-absorbing barriers. It does not provide background on the subject, overall findings, applications, recommendations, or suggested research.
From page 306...
... C-4 C H A P T E R C - 2 Study Locations Five locations with sound-reflecting barriers were studied in Phase 1, and three locations with soundabsorbing barriers were studied in Phase 2. Table 1 provides details.
From page 307...
... Table 1. Studied locations, Phases 1 and 2.
From page 308...
... C-6 Table 2. I-24 microphone positions.
From page 309...
... C-7 The microphone positions are described in Table 3. Table 3.
From page 310...
... C-8 Table 4. SR-71 microphone positions.
From page 311...
... C-9 MD-5, Hughesville, MD (Location EA-5, Sound-reflecting Barrier) The measurements at the MD-5 location were conducted on June 9, 2015.
From page 312...
... C-10 I-75, Troy, OH (Location OH-1, Sound-absorbing Barrier) The measurements at the I-75 location were conducted on Tuesday, November 15, 2016, from approximately 17:00 to 21:00.
From page 313...
... C-11 I-70, Troy, OH (Location OH-2, Sound-absorbing Barrier) Measurements were conducted on Wednesday, November 16, 2016, from approximately 14:30 to 18:30.
From page 314...
... C-12 C H A P T E R C - 3 Measured Broadband Level Differences at Reference Microphones Between the Road and the Barrier A Phase 1 finding was that the measured broadband unweighted sound pressure levels and A-weighted sound levels were generally higher at the Barrier microphones than at the No Barrier microphones. This finding held for the reference microphone located midway between the barrier and the road for the I-24 and SR-71 sound-reflecting barriers.
From page 315...
... C-13 Figure 7. Differences in running Leq (5 min.)
From page 316...
... C-14 2.6 dB, averaging approximately 1.4 dB higher; the A-weighted levels are higher by a range of 0.2 dB to 1.8 dB, averaging approximately 1.4 dB higher. Figure 9.
From page 317...
... C-15 Figure 10. Differences in running Leq (5 min.)
From page 318...
... C-16 C H A P T E R C - 4 Measured Broadband Level Differences at the Community Microphones Across the Road from the Barrier The higher levels seen opposite the sound-reflecting barriers were also seen to some extent for the soundabsorbing barriers. At the I-24, MD-5 and I-70 locations, the community microphones were at the same distances from the road, but at different heights above the road.
From page 319...
... C-17 Figure 11. Differences in running Leq (5 min.)
From page 320...
... C-18 For MD-5 (sound-reflecting barrier) , Figure 13 shows the differences in the unweighted and A-weighted levels for BarCom03 and NoBarCom05 (lower microphones)
From page 321...
... C-19 Figure 14. Differences in running Leq (5 min.)
From page 322...
... C-20 Figure 15. Differences in running Leq (5 min.)
From page 323...
... C-21 Community Microphones at Different Distances At the two sound-reflecting locations (I-90 and SR-71) and at the sound-absorbing location (I-75)
From page 324...
... C-22 Figure 18. Differences in running Leq (5 min.)
From page 325...
... C-23 Figure 19. Differences in running Leq (5 min.)
From page 326...
... C-24 for the more distant BarCom04 and NoBarCom06 positions. At BarCom04, the unweighted levels range from 0.5 dB lower than at NoBarCom06 to 1.9 dB higher, averaging approximately 0.6 dB higher.
From page 327...
... C-25 C H A P T E R C - 5 One-Third Octave Band Differences for Equivalent Leq (5 min.) Periods In the data analysis for the FHWA Method (comparing one-third octave band levels at Barrier and equivalent No Barrier sites)
From page 328...
... C-26 Figure 23. Averages of the differences in Leq (5 min.)
From page 329...
... C-27 For MD-5 (sound-reflecting barrier) , Figure 24 shows the results for the Downwind Neutral class.
From page 330...
... C-28 Figure 24. Averages of the differences in Leq (5 min.)
From page 331...
... C-29 For the sound-absorbing I-70 barrier, Figure 25 shows in the upper graph that , in general, the BarRef01 levels are less than 1 dB higher than the NoBarRef02 levels across most of the spectrum, from 80 Hz through 3.15 kHz. Below 63 Hz, the BarRef01 levels are from 1 dB to 3 dB higher, and above 3.15 kHz, 1.2 dB to 2 dB higher.
From page 332...
... C-30 Figure 25. Averages of the differences in Leq (5 min.)
From page 333...
... C-31 Community Microphones at Different Distances The I-90, SR-71, and I-75 locations had the community microphones pairs at different distances from each other. In general, the I-90 and SR-71 sound-reflecting barrier results showed greater differences in Barrier/No Barrier levels at the community microphones than for the sound-absorbing I-75 barrier.
From page 334...
... C-32 Figure 26. Averages of the differences in Leq (5 min.)
From page 335...
... C-33 For SR-71 (sound-reflecting barrier) , Figure 27 shows the averages of the differences in the Barrier and No Barrier microphones' levels for all the Downwind Neutral groups.
From page 336...
... C-34 Figure 27. Averages of the differences in Leq (5 min.)
From page 337...
... C-35 For the sound-absorbing I-75 barrier, Figure 28 shows the results for an average of all the Calm Inversion groups. In the upper graph, the BarRef01 levels are approximately 0.6 dB to 2.7 dB higher than the NoBarRef02 levels across the entire spectrum, except at 20 Hz, where the difference is only 0.2 dB.
From page 338...
... C-36 Figure 28. Averages of the differences in Leq (5 min.)
From page 339...
... C-37 C H A P T E R C - 6 Broadband L90 and L99 Statistical Descriptors In addition to the examination of the differences in levels for the equivalent pairs of running 5-minute Leq data, the differences in the Ln des criptors for the overall data without segregation into equivalent periods were investigated. The focus was on the possible change in the background level in the presence of the noise barrier.
From page 340...
... C-38 Figure 29. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-24, BarRef01 and NoBarRef02.
From page 341...
... C-39 Figure 31. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-24, BarCom04 and NoBarCom06.
From page 342...
... C-40 Figure 32. Differences in broadband A-weighted 5-minute L90, L99 and Leq, MD-5, BarCom03 and NoBarCom05.
From page 343...
... C-41 For the sound-absorbing I-70 barrier, Figure 34 presents the reference microphone differences, computed as BarRef01 minus NoBarRef02. The results show that while the A-weighted Leq (5 min.)
From page 344...
... C-42 Figure 35. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-70, BarCom03 and NoBarCom05.
From page 345...
... C-43 Community Microphones at Different Distances The I-90 (sound-reflecting barrier) , SR-71 (sound-reflecting barrier)
From page 346...
... C-44 Figure 38. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-90, BarCom04 and NoBarCom06.
From page 347...
... C-45 NoBarCom06 to 5.4 dB higher. During this time period, the meteorological class was Downwind Neutral.
From page 348...
... C-46 Figure 41. Differences in broadband A-weighted 5-minute L90, L99 and Leq, SR-71, BarCom04 and NoBarCom06.
From page 349...
... C-47 Figure 42. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-75, BarRef01 and NoBarRef02.
From page 350...
... C-48 Figure 43. Differences in broadband A-weighted 5-minute L90, L99 and Leq, I-75, BarCom03 and NoBarCom05.
From page 351...
... C-49 C H A P T E R C - 7 Ln Descriptors for One-Third Octave Bands The preceding analysis was for the broadband A-weighted sound levels and unweighted sound pressure levels. The following analysis examines the data in terms of one-third octave bands by use of color shading.
From page 352...
... C-50 Figure 46 presents the I-24 Ln differences for BarCom03 and NoBarCom05, while Figure 47 presents the Ln differences for BarCom04 and NoBarCom06. Some evidence exists of slightly higher Ln values at BarCom03 vs.
From page 353...
... C-51 For I-90 (sound-reflecting barrier) , Figure 48 compares BarRef01 and NoBarRef02 levels.
From page 354...
... C-52 Figure 50. I-90 Differences in Ln (5 min.)
From page 355...
... C-53 Figure 52. SR-71 Differences in Ln (5 min.)
From page 356...
... C-54 Figure 54. MD-5 Differences in Ln (5 min.)
From page 357...
... C-55 Figure 55. MD-5 Differences in Ln (5 min.)
From page 358...
... C-56 Figure 56. MD-5 Differences in Ln (5 min.)
From page 359...
... C-57 Figure 57. I-75 Differences in Ln (5 min.)
From page 360...
... C-58 Figure 59. I-75 Differences in Ln (5 min.)
From page 361...
... C-59 Figure 61. I-70 Differences in Ln (5 min.)
From page 362...
... C-60 C H A P T E R C - 8 Spectrograms Spectrograms show the frequency content of sound as a function of time. This section qualitatively compares Phase 1 and Phase 2 results of the spectrogram analysis before comparing the difference spectrograms.
From page 363...
... C-61 Figure 63. I-24 (sound-reflecting barrier)
From page 364...
... C-62 Figure 64. I-24 (sound-reflecting barrier)
From page 365...
... C-63 Figure 65. I-24 (sound-reflecting barrier)
From page 366...
... C-64 the community side of the highway, BarCom03 and NoBarCom05 (69 ft. from the center of the near travel lane)
From page 367...
... C-65 In addition to examining vehicle pass-by events at the I-90 location, spectrograms for larger blocks of data were studied. Figure 67 provides an example for the near microphones (BarCom03/NoBarCom05)
From page 368...
... C-66 For SR-71 (sound-reflecting barrier) , spectrograms for a group of trucks traveling southbound are shown in Figure 68.
From page 369...
... C-67 In addition to the vehicle pass-by events, blocks of data were also examined for SR-71. Figure 69 is for a 4-minute block of clean data in the morning at 09:49 and shows a clear difference between the Barrier and No Barrier sites at the far microphones.
From page 370...
... C-68 Spectrograms for an MD-5 (sound-reflecting barrier) vehicle pass-by event are shown in Figure 70.
From page 371...
... C-69 In addition to examining vehicle pass-by events, spectrograms for blocks of data were also examined at the MD-5 location. Figure 71 provides an example for the upper microphones (BarCom04/NoBarCom06)
From page 372...
... C-70 Spectrograms for the sound-absorbing I-75 barrier location are discussed here. Figure 72 through Figure 74 are for a 5-minute time block from 17:55 to 18:00 for the barrier-side (reference)
From page 373...
... C-71 Figure 72. I-75 (sound-absorbing barrier)
From page 374...
... C-72 Figure 73. I-75 (sound-absorbing barrier)
From page 375...
... C-73 Figure 74. I-75 (sound-absorbing barrier)
From page 376...
... C-74 Figure 75. I-75 (sound-absorbing barrier)
From page 377...
... C-75 Figure 76. I-75 (sound-absorbing barrier)
From page 378...
... C-76 For the I-70 sound-absorbing barrier location, spectrograms for a 5-minute data block are shown in Figure 77 through Figure 79. Figure 77 is for the barrier-side (reference)
From page 379...
... C-77 Figure 77. I-70 (sound-absorbing barrier)
From page 380...
... C-78 Figure 78. I-70 (sound-absorbing barrier)
From page 381...
... C-79 Figure 79. I-70 (sound-absorbing barrier)
From page 382...
... C-80 Figure 80. I-70 (sound-absorbing barrier)
From page 383...
... C-81 Figure 81. I-70 (sound-absorbing barrier)
From page 384...
... C-82 C H A P T E R C - 9 Difference Spectrograms and Comb Filtering This portion of the comparison of the Phase 1 and Phase 2 results focuses on spectrogram differences. Key elements of the comparison are: The research team developed a method to visualize spectrogram differences for the same vehicle passing by a Barrier site and an equivalent No Barrier site.
From page 385...
... C-83 second figure of each pair is a plot showing a slice in time that reveals the peaks in differences by one-third octave band frequency. Examination of the spectrogram difference plots reveals lines of hot spots across the spectrograms, particularly just before and after the maximum sound level of the event.
From page 386...
... C-84 delay of 10 ms, this corresponds to a repetition pitch of 1/0.010 = 100 Hz. Longer delay times result in lower-frequency repetition pitches.
From page 387...
... C-85 Figure 82. Spectrogram difference plot for MD-5 (sound-reflecting barrier)
From page 388...
... C-86 Figure 83. Differences at time -2 seconds from maximum; MD-5 (sound-reflecting barrier)
From page 389...
... C-87 Figure 84. Spectrogram difference plot for MD-5 (sound-reflecting barrier)
From page 390...
... C-88 Figure 85. Differences at time -0.5 seconds from maximum; MD-5 (sound-reflecting barrier)
From page 391...
... C-89 Figure 86. Spectrogram difference plot for I-90 (sound-reflecting barrier)
From page 392...
... C-90 Figure 87. Differences at time +2.7 seconds from maximum; I-90 (sound-reflecting barrier)
From page 393...
... C-91 Figure 88. Spectrogram difference plot for I-90 (sound-reflecting barrier)
From page 394...
... C-92 Figure 89. Differences at time +1.75 seconds from maximum; I-90 (sound-reflecting barrier)
From page 395...
... C-93 Figure 90. Spectrogram difference plot for SR-71 (sound-reflecting barrier)
From page 396...
... C-94 Figure 91. Differences at time +1.5 seconds from maximum; SR-71 (sound-reflecting barrier)
From page 397...
... C-95 Figure 92. Spectrogram difference plot for SR-71 (sound-reflecting barrier)
From page 398...
... C-96 Figure 93. Differences at time +1.1 seconds from maximum; SR-71 (sound-reflecting barrier)
From page 399...
... C-97 Figure 94. Spectrogram difference plot for MD-5 (sound-reflecting barrier)
From page 400...
... C-98 Figure 95. Differences at time -3 seconds from maximum; MD-5 (sound-reflecting barrier)
From page 401...
... C-99 This could indicate that a twelfth-octave narrow-band analysis, or possibly an even narrower band analysis (showing all frequency content) , is needed to reveal what is truly happening on a frequency basis.
From page 402...
... C-100 Figure 96. Spectrogram difference plot for I-75 (sound-absorbing barrier)
From page 403...
... C-101 Figure 97. Differences at time 2.5 seconds from maximum; I-75 (sound-absorbing barrier)
From page 404...
... C-102 Figure 98. Spectrogram difference plot for I-75 (sound-absorbing barrier)
From page 405...
... C-103 Figure 99. Differences at time -0.25 seconds from maximum; I-75 (sound-absorbing barrier)
From page 406...
... C-104 Figure 100. Spectrogram difference plot for I-70 (sound-absorbing barrier)
From page 407...
... C-105 Figure 101. Differences at time -0.75 seconds from maximum; I-70 (sound-absorbing barrier)
From page 408...
... C-106 Figure 102. Spectrogram difference plot for I-70 (sound-absorbing barrier)
From page 409...
... C-107 Figure 103. Differences at time -2 seconds from maximum; I-70 (sound-absorbing barrier)
From page 410...
... C-108 Figure 104. Spectral difference plots for vehicle pass-by events for all sound-reflecting and soundabsorbing barrier sites.
From page 411...
... C-109 R E F E R E N C E S Frans A Bilsen and Roelof J
From page 413...
... D-1 Using the Barrier Reflections Screening Tool A P P E N D I X D Judy Rochat and Keith Yoerg ATS ConSulTing Pasadena, CA
From page 414...
... D-2 CONTENTS CHAPTER D-1 .................................................................................................................................... D-3 Intended Use .........................................................................................................................................................

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