National Academies Press: OpenBook
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Suggested Citation:"Front Matter." 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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Suggested Citation:"Front Matter." 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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Suggested Citation:"Front Matter." 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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Suggested Citation:"Front Matter." 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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Suggested Citation:"Front Matter." 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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Suggested Citation:"Front Matter." 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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Suggested Citation:"Front Matter." 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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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2009 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 635 Subject Areas Energy and Environment • Highway and Facility Design Acoustic Beamforming: Mapping Sources of Truck Noise Yuriy A. Gurovich Kenneth J. Plotkin Daniel H. Robinson WYLE LABORATORIES INC. Arlington, VA William K. Blake Bethesda, MD Paul R. Donavan ILLINGWORTH & RODKIN, INC. Petaluma, CA Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board’s recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 635 Project 08-56 ISSN 0077-5614 ISBN 978-0-309-11800-2 Library of Congress Control Number 2009935879 © 2009 Transportation Research Board COPYRIGHT PERMISSION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The project that is the subject of this report was a part of the National Cooperative Highway Research Program conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. Such approval reflects the Governing Board’s judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration, U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council. The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of this report.

CRP STAFF FOR NCHRP REPORT 635 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Christopher J. Hedges, Senior Program Officer Eileen P. Delaney, Director of Publications Natalie Barnes, Editor Doug English, Editor NCHRP PROJECT 08-56 PANEL Field of Transportation Planning—Area of Forecasting Kenneth D. Polcak, Maryland State Highway Administration, Baltimore, MD (Chair) Bruce C. Rymer, California DOT, Sacramento, CA Mariano Berrios, Florida DOT, Tallahassee, FL Robert M. Clarke, R.M. Clarke Counsulting, Caswell Beach, NC Deborah Freund, Federal Motor Carrier Safety Administration, Washington, DC Thomas A. Koos, Kentucky Transportation Cabinet, Frankfort, KY Larry J. Magnoni, Washington State DOT, Seattle, WA Judith L. Rochat, Research and Innovative Technology Administration, Cambridge, MA Michael A. Tunnell, American Transportation Research Institute, W. Sacramento, CA Mark A. Ferroni, FHWA Liaison Kimberly Fisher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 08-56 by Wyle Laboratories, Inc., in Arlington, Virginia. Wyle Laboratories is the contractor for this study, with Dr. William Blake as the team consultant, and Illingworth & Rodkin, Inc. as the subcontractor. Proof-of-concept tests were performed at the International Truck and Engine Corporation’s Truck Development and Technology Center in Ft. Wayne, Indiana. Dr. Kenneth Plotkin, Chief Scientist of Wyle Laboratories, was the Principal Investigator. The other authors of this report are Dr. Yuriy Gurovich, Acoustic Engineering Manager, and Daniel Robinson, Acoustical Engineer, of Wyle Laboratories; Dr. William Blake; and Dr. Paul Donavan of Illingworth & Rodkin. The authors are grateful to Mr. Les A. Grundman, Mr. Lee E. Schroeder, Mr. Chukwunonso Okoli and other International Truck employees for their invaluable active support during the proof-of-concept test- ing in Ft. Wayne. The authors also acknowledge Mr. Kenneth Polcak of the Maryland State Highway Administration for his assistance in conducting roadside truck noise measurements on US 301. C O O P E R A T I V E R E S E A R C H P R O G R A M S

This report documents the use of the acoustic beamforming technique to pinpoint and measure noise levels from heavy truck traffic. The system 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. The results validate the feasibility of beamforming technology, offer new insight into the distribution of truck noise sources, and provide valuable input to the design and testing of quieter pavements and noise barrier systems. This report will be of interest to anyone con- cerned with understanding and mitigating highway noise levels. Heavy trucks are significant contributors to overall traffic noise levels, and transporta- tion agencies need to better understand the location and relative levels of the principal noise sources (e.g., exhaust, mechanical, tire–pavement, and aerodynamic) on heavy vehicles in order to more successfully mitigate traffic noise impacts. Typical measures used to mitigate highway traffic noise include noise barriers, land use planning, and insulation of structures. Some transportation agencies are investigating additional measures, such as quiet pavements. Newer acoustical measurement and map- ping techniques such as beamforming show promise for isolating the location and extent of the primary noise sources emanating from heavy trucks. Under NCHRP Project 08-56, a research team led by Wyle Laboratories designed and fabricated an elliptical beamform- ing array and tested a proof-of-concept design on stationary and moving trucks in a con- trolled setting. The tests were validated using known sound sources such as loudspeakers mounted on the vehicles. The resulting data were analyzed in the laboratory, and the tests validated the array’s ability to localize and evaluate individual noise sources from the test vehicles. Following the proof-of-concept testing, the beamforming technique was used to measure truck noise sources under actual operating conditions on US 301 in Maryland. A total of 59 heavy truck and 4 medium truck pass-bys were measured, analyzed, and inter- preted. The results showed acoustic beamforming to be a very appropriate method for truck noise measurement and enabled the research team to optimize the microphone array and software for this purpose. The system was effective in isolating and measuring noise sources for both stationary and moving trucks with frequencies between 250 and 2000 Hz. The report includes a number of recommendations, including the updating of current traf- fic noise models, development of a national database for traffic noise models on different pavement types, and the further application of the study results to evaluate pavement and noise barrier designs. F O R E W O R D By Christopher J. Hedges Staff Officer Transportation Research Board

C O N T E N T S 1 Summary 6 Chapter 1 Background 6 1.1 Introduction 6 1.2 Heavy Truck Noise Sources 7 1.3 Source Identification Methods 9 1.4 Objective and Scope of Research 10 Chapter 2 Research Approach 10 Task 1. Analyze Literature, Research, and Current Practice 10 Task 2. Develop Experimental Design 10 Task 3. Perform Proof-of-Concept Test 10 Task 4. Submit Interim Report 10 Task 5. Execute Testing Plan 11 Task 6. Document and Analyze Results 11 Task 7. Summarize Key Findings 11 Task 8. Identify Future Research and Testing Needs 11 Task 9. Submit Final Report 12 Chapter 3 Research Findings 12 3.1 Review of Beamforming for Vehicle Noise Source Identification 12 3.2 Development of Experimental Design 12 3.2.1 Noise Mapping Technique Development 13 3.2.2 Microphone Array Design 14 3.2.3 Balance between Array Aperture and Spherical Spreading Loss 17 3.2.4 Design Conclusions 19 3.3 Experimental Microphone Array Engineering 19 3.3.1 Mechanical Design 19 3.3.2 Data Acquisition System 19 3.3.3 Preliminary Testing 20 3.4 Proof-of-Concept Testing 20 3.4.1 Low-Speed Tests 22 3.4.2 High-Speed Tests 23 3.4.3 Passby and Intensity Measurements 31 3.5 Proof-of-Concept Test Results 31 3.5.1 Beamformer Calibrations with Spherical Source 34 3.5.2 Benchmark Measurements of Spherical Source on Moving Truck with Competing Truck Noise 35 3.5.3 Benchmark Parallel Array-Based and Acoustic Intensity Measurements for Stationary Trucks

41 3.5.4 Example Results from Low- and High-Speed Track Passbys 41 3.5.4.1 Analysis Technique for Low- and High-Speed Track Passbys 44 3.5.4.2 Passby Evaluations of the 5900i Truck: Localization of Engine Compartment and Tire Noise 46 3.5.4.3 Passby Evaluations of the 9200i Truck: Localization of Engine Compartment and Exhaust Noise 48 3.5.4.4 Evaluations of the Truck Acoustic Source Level During Passby as a Function of Vertical Elevation 53 3.6 Roadside Testing 53 3.6.1 Microphone Array Modifications 53 3.6.2 Data Post-Processing Algorithm Modifications 54 3.6.3 Test Site Selection 54 3.6.4 Roadside Measurement Setup 55 3.7 Results of Roadside Measurements 55 3.7.1 Calibration of the Test Site Geometry 55 3.7.2 Image Results of the Vehicle Passbys 68 3.7.3 Example Model of Truck Sources for Simulating Noise Propagation Results of the Vehicle Passbys 71 Chapter 4 Conclusions and Recommendations 71 4.1 Conclusions 71 4.2 Recommendations 73 References 75 Appendix A Array Microphone Coordinates 76 Appendix B Vertical Distributions of Noise Sources for Heavy Trucks 78 Appendix C Glossary of Special Terms

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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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