NCHRP Report 635: Acoustic Beamforming: Mapping Sources of Truck Noise

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

Table of Contents

Front Matter R1-R9

Summary 1-5

1.2 Heavy Truck Noise Sources 6-6

1.3 Source Identification Methods 7-8

1.4 Objective and Scope of Research 9-9

Task 5. Execute Testing Plan 10-10

Task 9. Submit Final Report 11-11

3.2.1 Noise Mapping Technique Development 12-12

3.2.2 Microphone Array Design 13-13

3.2.3 Balance Between Array Aperture and Spherical Spreading Loss 14-16

3.2.4 Design Conclusions 17-18

3.3.3 Preliminary Testing 19-19

3.4.1 Low-Speed Tests 20-21

3.4.2 High-Speed Tests 22-22

3.4.3 Passby and Intensity Measurements 23-30

3.5.1 Beamformer Calibrations with Spherical Source 31-33

3.5.2 Benchmark Measurements of Spherical Source on Moving Truck with Competing Truck Noise 34-34

3.5.3 Benchmark Parallel Array-Based and Acoustic Intensity Measurements for Stationary Trucks 35-40

3.5.4.1 Analysis Technique for Low- and High-Speed Track Passbys 41-43

3.5.4.2 Passby Evaluations of the 5900i Truck: Localization of Engine Compartment and Tire Noise 44-45

3.5.4.3 Passby Evaluations of the 9200i Truck: Localization of Engine Compartment and Exhaust Noise 46-47

3.5.4.4 Evaluations of the Truck Acoustic Source Level During Passby as a Function of Vertical Elevation 48-52

3.6.2 Data Post-Processing Algorithm Modifications 53-53

3.6.4 Roadside Measurement Setup 54-54

3.7.2 Image Results of the Vehicle Passbys 55-67

3.7.3 Example Model of Truck Sources for Simulating Noise Propagation Results of the Vehicle Passbys 68-70

4.2 Recommendations 71-72

References 73-74

Appendix A - Array Microphone Coordinates 75-75

Appendix B - Vertical Distributions of Noise Sources for Heavy Trucks 76-77

Appendix C - Glossary of Special Terms 78-79

Abbreviations used without definitions in TRB publications 80-80