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Acoustic Beamforming: Mapping Sources of Truck Noise (2009)

Chapter: Chapter 2 - Research Approach

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Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Acoustic Beamforming: Mapping Sources of Truck Noise. Washington, DC: The National Academies Press. doi: 10.17226/14311.
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Page 10
Page 11
Suggested Citation:"Chapter 2 - Research Approach." National Academies of Sciences, Engineering, and Medicine. 2009. Acoustic Beamforming: Mapping Sources of Truck Noise. Washington, DC: The National Academies Press. doi: 10.17226/14311.
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Page 11

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10 Task 1. Analyze Literature, Research, and Current Practice A review was conducted of current noise source identifica- tion techniques. Emphasis was on beamforming, which had been demonstrated to be generally suitable for this type of measurement. A major objective of the literature review was to quantify frequencies, distances, array sizes, etc., to ensure that the array developed for this project would reflect the current state of the art. The recent work by I&R for Caltrans provided key data for analysis of these issues, particularly for investigat- ing array size, frequency range, and spatial resolution. Results of the review of current noise source identification techniques are presented in Chapter 3. Task 2. Develop Experimental Design Two separate experimental tasks were proposed in this project to develop a practical measurement technique for quantifying truck noise sources. The first experimental task was the design and validation of a noise source mapping tech- nique through proof-of-concept tests on a limited number of trucks and pavements, with emphasis on validating the noise mapping method. This proof-of-concept test was completed in Tasks 2 and 3 and is described in Chapter 3. Task 3. Perform Proof-of-Concept Test The technology demonstration was accomplished through the proof-of-concept testing with the assistance of Inter- national Truck and Engine Corporation (IT) at their proving grounds in Fort Wayne, Indiana, in July 2006. A limited but representative sample of trucks was selected from the vehicle test matrix developed in the previous task and available at IT. The beamforming tests were conducted on a stationary truck operating under different conditions, were validated using known sound sources such as loudspeakers added to the vehi- cle, and then were conducted with trucks performing a series of passby procedures. Beamforming measurements were con- ducted for a number of test configurations. The proof-of-concept test data were post-processed and analyzed in a laboratory. This analysis included an experimen- tal evaluation of various performance characteristics of the array measurement system, comparison with the theoretical parameters specified earlier for the array in the design stage, as well as example results for truck passbys at low- and high-speed tracks with localization and identification of individual noise sources for the tested trucks. Task 4. Submit Interim Report The interim report summarizing the results of Tasks 1 through 3 was submitted in July 2007. It presents the results of the literature search, development of the experimental design, and the proof-of-concept tests. Following a review and meet- ing with the NCHRP, comments by the NCHRP were accom- modated in the experimental design and testing plan for the remaining tasks. Work on the subsequent tasks proceeded fol- lowing NCHRP approval. Task 5. Execute Testing Plan The second experimental task of the project, application of the validated method to quantify noise sources on typical heavy trucks, was accomplished through noise mapping of a number of trucks under actual roadside conditions on an in- service highway. Prior to the mapping, the necessary adjust- ments to the technique identified during the proof-of-concept testing of Task 3 were performed. The roadside testing was conducted in April 2008 with the beamforming system collect- ing data for a wide range of trucks and various operating con- ditions on a selected highway (US 301). One hundred vehicle passbys were recorded in one day of testing using the measure- ment system developed. C H A P T E R 2 Research Approach

Task 6. Document and Analyze Results The roadside test data were again post-processed in a laboratory. The analysis included an experimental evalua- tion of the spectral content of the measured truck pass- bys and the vertical distribution of the noise from truck sources, as well as statistical assessment for multiple pass- bys. The results of the testing are presented and discussed in Chapter 3. Task 7. Summarize Key Findings The key findings of the study are summarized and pre- sented in the Summary of this report. Task 8. Identify Future Research and Testing Needs Potential areas for follow-up research to and application of the truck noise source mapping technique developed in the study for further truck testing are identified and presented in Chapter 4. Task 9. Submit Final Report This final report incorporates the interim report material revised according to the NCHRP comments, includes the new results for the roadside truck testing, summarizes the key findings of the study, and identifies the future research and testing needs. 11

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 635: Acoustic Beamforming: Mapping Sources of Truck Noise explores the acoustic beamforming technique in an attempt to pinpoint and measure noise levels from heavy truck traffic. The beamforming technique uses an elliptical array of more than 70 microphones and data acquisition software to measure noise levels from a variety of noise sources on large trucks—including the engine, tires, mufflers, and exhaust pipes.

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