Download or read book Parallel Barrier Effects for Distant Receivers written by and published by . This book was released on 2002 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: The research described in this report determined the effects of parallel noise barriers as a contributing factor to the perception of increased noise levels by distant receivers. Data to quantify the characteristics of noise propagation was acquired at the HAM-71-11.44 and SUM-8-6.8 parallel barrier sites. Both sites had complaints of increased noise levels due to barrier construction. An in-situ test system using a point source was devised and developed to identify the existence, location, and relative intensity of reflections between parallel noise barriers. Multiple reflections from barrier walls existed at each receiver location for all parallel barrier sites tested. The reflections increased noise levels for receivers from below 1 dB for receivers closest to the noise barriers, to increases approaching the theoretical maximum of 3 dB for receivers farther from the noise barriers. Reflection contributions to receiver sound levels increased with greater receiver distance from the highway up to 120 m from the noise barrier. A mean barrier attenuation of 2-4 dB was predicted for modeled receivers 180m to 420m from the near barrier. The propagation path height change with the barrier construction increased received levels from a test signal point source by an average of 3 to 4 dB, but as much as 14 dB for receivers 180m to 360m from the barriers. The increase in received levels was attributed to a reduction in ground attenuation caused by the increased ray path height following barrier construction. The sound-absorbing panels used to retrofit the west side noise barrier on the Summit 8 project substantially reduced the contribution of reflections for east side receivers. The reduction in reflection contributions due to the sound-absorbing panels was greater for receivers at increased distances from the highway. The results of the investigation support the hypothesis that many of these distant receivers realized little barrier attenuation following noise barrier construction. Further, the amount of barrier attenuation realized was in many cases more than offset by the loss in ground attenuation due to the change in noise path height due to barrier construction. Finally, reflections between parallel noise barriers increased noise levels above the levels expected for single barriers.