Mechanical Engineering Grad Theses


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Rose-Hulman Institute of Technology
Rose-Hulman Scholar
Graduate Theses - Mechanical Engineering

Mechanical Engineering

Spring 5-2015
The Development and Evaluation of a Method for Understanding the Impact of Transmission Loss On the Overall Noise Attenuation of Finite Barriers
Ashwin Arvind Upasani
Rose-Hulman Institute of Technology

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Recommended Citation
Upasani, Ashwin Arvind, "The Development and Evaluation of a Method for Understanding the Impact of Transmission Loss On the Overall Noise Attenuation of Finite Barriers" (2015). Graduate Theses - Mechanical Engineering. Paper 3.
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THE DEVELOPMENT AND EVALUATION OF A METHOD FOR UNDERSTANDING THE IMPACT OF TRANSMISSION LOSS ON THE
OVERALL NOISE ATTENUATION OF FINITE BARRIERS
A Thesis Submitted to the Faculty
of Rose-Hulman Institute of Technology
by
Ashwin Arvind Upasani
In Partial Fulfillment of the Requirements for the Degree of
Master of Science in Mechanical Engineering
May 2015
© Ashwin Arvind Upasani

ABSTRACT
Upasani, Ashwin Arvind M.S.M.E Rose-Hulman Institute of Technology May 2015 The Development and Evaluation of a Method for Understanding the Impact of Transmission Loss on the Overall Noise Attenuation of Finite Barriers Thesis Advisor: Dr. Darrell Gibson
The purpose of this study is to evaluate the impact of transmission loss on the overall noise reduction obtained from finite barriers. The noise attenuation ability of barriers is understood to be a consequence of sound waves diffracting around their edges. Although the presence of transmission loss is acknowledged, its significance in affecting noise attenuation is usually not considered a priority in barrier design. This study incorporates the Fresnel Number concept for predicting theoretical insertion loss of a finite barrier and compares these predictions to experimental observations. The experiments performed in this study offer a method to isolate the transmission loss component from diffraction based noise attenuation. This isolation allows the comparison of these two factors in the overall barrier performance. The influence of transmission loss is found to be significant and the findings encourage its consideration in designing solutions to modern noise control challenges.

DEDICATION
In Memory of Abhishek Bangale An Optimist, A True Friend, An Undaunted Fighter
Always Present, in the Good Times and the Bad

ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to Dr. Darrell Gibson for his assistance and guidance during this study. I would also like to express my gratefulness to Dr. Eva Andrijcic and Dr. Jerry Fine for their continuous support and invaluable advice during my research work. As my advisory committee, their encouragement has been fundamental to my academic journey at Rose-Hulman Institute of Technology.
I would like to extend a special thank you to Dr. Edward Wheeler for providing access to his lab, which made the experimental investigations in this study possible.
I would also like to convey my gratefulness to the Learning Center for proofreading my drafts and offering crucial suggestions. My sincere appreciation also goes to the Library staff, especially Bernadette Ewen and Amy Harshbarger for their indispensible efforts in providing research materials that were essential for this study. A special thank you also to the Graduate Office for providing the financial opportunities that encourage and support graduate research.
My most sincere appreciation goes to my parents and my family. Their encouragement and hard work has been vital in providing an environment full of opportunities and possibilities for success.
Last but not the least, I would like to express my deepest gratitude to Isabella Magni for her assistance with the experiments and draft corrections. Her encouragement, kindness, and unconditional support have been fundamental to this journey for which I will be forever grateful.

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TABLE OF CONTENTS
LIST OF FIGURES ...................................................................................................................... v LIST OF TABLES ...................................................................................................................... vii LIST OF ABBREVIATIONS ................................................................................................... viii LIST OF SYMBOLS ................................................................................................................... ix GLOSSARY................................................................................................................................... x Chapter I: INTRODUCTION ..................................................................................................... 1 Chapter II: BACKGROUND....................................................................................................... 4
2.1 TYPES OF BARRIERS............................................................................................................... 5 2.1.1 Semi-Infinite Barriers .................................................................................................... 5 2.1.2 Finite Barriers ................................................................................................................ 5 2.1.3 Reflective Barriers ......................................................................................................... 5 2.1.4 Absorptive Barriers ........................................................................................................ 7
2.2 FACTORS AFFECTING BARRIER PERFORMANCE: .................................................................... 8 2.2.1 Barrier Height and the Proximity of Source and Receiver from the Barrier ................. 8 2.2.2 Sound Absorbing Material ............................................................................................. 8 2.2.3 Surface of the Source ..................................................................................................... 9 2.2.4 Frequency of Sound and its Effect on Diffraction ....................................................... 10 2.2.5 Transmission Loss ....................................................................................................... 11
Chapter III: LITERATURE REVIEW .................................................................................... 13 3.1 SOUND PRESSURE LEVEL (SPL)........................................................................................... 13 3.2 DIFFRACTION THEORY ......................................................................................................... 15

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3.2.1 Noise Attenuation from Semi-Infinite Barriers ........................................................... 15 3.2.2 Noise Attenuation from Finite Barriers ....................................................................... 17 3.3 TRANSMISSION LOSS............................................................................................................ 20
3.3.1 Transmission Coefficient ............................................................................................. 20 3.3.2 Limp-wall Mass Law ................................................................................................... 22 3.3.3 Impact of Material Stiffness......................................................................................... 24 3.3.4 Standard Method for Measuring Transmission Loss ................................................... 27 3.4 ACOUSTICAL REVERBERATIONS........................................................................................... 28
3.4.1 Direct and Reflected Sound ......................................................................................... 28 3.4.2 Reverberant Sound Field.............................................................................................. 30 3.4.3 Anechoic Chambers ..................................................................................................... 31 3.5 METHODS FOR EVALUATING BARRIER INSERTION LOSS ...................................................... 34
3.5.1 Experimental Measurements........................................................................................ 34 3.5.2 Numerical Estimation: Ray Tracing Method ............................................................... 34 Chapter IV: THE EXPERIMENT ............................................................................................ 36
4.1 THE FRESNEL NUMBER CONCEPT ........................................................................................ 36
4.2 APPARATUS.......................................................................................................................... 37
4.2.1 The Sound Source ........................................................................................................ 37 4.2.2 The Barrier ................................................................................................................... 38 4.2.3 The Receiver ................................................................................................................ 39 4.3 REVERBERATION CONTROL ................................................................................................. 40
4.4 SETUP AND PROCEDURE....................................................................................................... 43
4.4.1 Initial Setup .................................................................................................................. 43 4.4.2 Ambient SPL Measurements ....................................................................................... 44 4.4.3 SPL Measurements before Barrier Insertion................................................................ 45 4.4.4 SPL Measurements after Barrier Insertion .................................................................. 46 4.4.5 Measuring Diffraction Paths for the Sound Waves ..................................................... 47 4.4.6 Precautions ................................................................................................................... 48 Chapter V: RESULTS AND DISCUSSION............................................................................. 49
5.1 THEORETICAL CALCULATION OF IL ..................................................................................... 49
5.2 COMPARING THEORETICAL CALCULATIONS TO EXPERIMENTAL OBSERVATIONS OF IL ....... 50
5.2.1 Barrier Insertion - 0.5 in. Thickness ............................................................................ 50

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5.2.2 Barrier Insertion - 1.0 in. Thickness ............................................................................ 51 5.2.3 Barrier Insertion - 1.5 in. Thickness ............................................................................ 52 5.2.4 Comparative Assessment of all Barrier Setups............................................................ 53 5.3 EFFECT OF CRITICAL RESONANCE FREQUENCY OF TL ON NOISE ATTENUATION ................. 55 5.4 EFFECT OF PANEL RESONANCES ON TL AND THE OVERALL NOISE ATTENUATION .............. 57 5.5 EFFECT OF BARRIER THICKNESS ON FREQUENCY SPECIFIC NOISE ATTENUATION ............... 58 5.6 HEALTH, SAFETY, AND DESIGN CONSIDERATIONS............................................................... 61
CHAPTER VI: LIMITATIONS................................................................................................ 63
CHAPTER VII: CONCLUSIONS AND FUTURE WORK ................................................... 65
7.1 CONCLUSIONS ...................................................................................................................... 65 7.2 FUTURE WORK..................................................................................................................... 67
LIST OF REFERENCES ........................................................................................................... 69
APPENDICES ............................................................................................................................. 71
APPENDIX A .............................................................................................................................. 72 APPENDIX B............................................................................................................................... 73 APPENDIX C............................................................................................................................... 75 APPENDIX D .............................................................................................................................. 76

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Mechanical Engineering Grad Theses