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Design of a Fully Anechoic Chamber

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Design of a Fully Anechoic Chamber Design of a Fully Anechoic Chamber Roman Rusz Master’s Degree Project TRITA-AVE 2015:36 ISSN 1651-7660 iii iv Preface This Thesis is the final project within the Master of Science program Mechanical Engineering with specialization in Sound and Vibration at the Marcus Wallenberg Laboratory for Sound and Vibration Research (MWL) at the department of Aeronautical and Vehicle Engineering at the KTH Royal Institute of Technology, Stockholm, Sweden. This Thesis was conducted at Honeywell, in partnership with Technical University of Ostrava, Ostrava, Czech Republic under the supervision of Ing. Václav Prajzner. Supervisor at KTH Royal Institute of Technology was Professor Leping Feng, Ph.D. v Acknowledgment To begin with, I would like to thank Ing. Michal Weisz, Ph.D., the main acoustician of the Acoustic department at Technical University of Ostrava. He was an excellent support during the project. I would like to thank him for sharing his experiences and knowledge in acoustics. I would also like to thank my supervisor Leping Feng, Ph.D. for his guidance in this project and for sharing his deep knowledge for the topic and all the teachers and professors at KTH Royal Institute of Technology for their support and assistance. I would like to give special thanks to: my beloved family. I thank you for your strong support during my studies at KTH Royal Institute of Technology. my dear friend Jakub Cinkraut for being such an amazing friend. I thank you for the countless hours we spent together in Sweden, Finland and Czech Republic. I would not enjoy my studies without you. my girlfriend Petra Gomolova for being such a wonderful partner. I thank you for all your support and encouragement during my studies in Stockholm. vi Table of Contents Preface ..................................................................................................................................... v Acknowledgment .....................................................................................................................vi Abstract .................................................................................................................................... ix List of abbreviations ................................................................................................................. x List of mathematical notations, indices and symbols .............................................................. xi 1. Introduction ..................................................................................................................... 1 1.1 Fully Anechoic Chamber ................................................................................................. 2 1.2 Objective ........................................................................................................................ 4 2. Theory .............................................................................................................................. 6 2.1. Free Field (Direct field) .................................................................................................. 7 2.2 Chamber Shape and Dimensions ................................................................................... 9 2.3 Room Modes .................................................................................................................. 9 2.3.1 Calculation of the Room Modes ............................................................................ 12 2.3.2 Preferred Room Dimensions According to Room Modes ..................................... 13 2.4 Wedge design ............................................................................................................... 14 2.4.1 Sound Absorption Material ................................................................................... 14 2.4.1.1 Main Absorber Categories ............................................................................. 14 2.4.1.2 Measurement Methods for Absorption and Impedance ............................... 16 2.4.1.3 The influence of air absorption ...................................................................... 20 2.4.2 Wedge Structure and Design ................................................................................ 21 2.4.3 Finite Element Method (FEM) Analyses of Wedge ............................................... 26 2.4.3.1 Properties of Bulk Reacting Material ............................................................. 28 2.4.3.2 Numerical Scheme ......................................................................................... 29 2.4.3.2 Design Curves for Reacting Wedges .............................................................. 30 2.5 Transmission loss ......................................................................................................... 37 2.5.1 Single wall.............................................................................................................. 38 2.5.1.1 Critical frequency (Coincidence frequency) ................................................... 38 2.5.1.2 Infinite panel .................................................................................................. 39 2.5.1.3 Finite panel ..................................................................................................... 40 2.5.2 Double wall............................................................................................................ 41 2.5.3 Transfer Matrix Method (TMM) ............................................................................ 41 2.5.3.1 Thin Elastic Panel............................................................................................ 42 2.5.3.2 Fluid layer ....................................................................................................... 43 2.5.3.3 Porous layer ................................................................................................... 44 vii 2.5.3.4 Interface to/from porous layer ...................................................................... 44 2.5.3.5 Transmission factor from transfer matrix ...................................................... 45 2.5.4 Sound Propagation through Multiple Partitions ................................................... 46 2.6 Vibration Isolation ........................................................................................................ 46 2.6.1 Vibration Isolators ................................................................................................. 50 2.6.2 Isolator Selection ................................................................................................... 53 2.7 Calibration of the Anechoic Chamber .......................................................................... 54 3. Design of the Anechoic Chamber ....................................................................................... 56 3.1 Shape and Dimensions of the Chamber Design ....................................................... 57 3.2 Room modes calculation .......................................................................................... 57 3.3 Sound Absorption Material Design .......................................................................... 59 3.4 Wedge Structure and Design ................................................................................... 60 3.4.1 Wedge structure ............................................................................................... 61 3.4.2 Wedge Dimensions Design ................................................................................ 61 3.5 Transmission Loss (TL) .............................................................................................. 64 3.5.1 Wall Transmission Loss ..................................................................................... 64 3.5.2 Doors Transmission Loss ................................................................................... 66 3.5.3 Average Transmission Loss ............................................................................... 68 3.6 Vibration Isolation .................................................................................................... 68 3.7 Conclusions .............................................................................................................. 72 References.............................................................................................................................. 74 Appendix ................................................................................................................................ 76 1. Vibration isolation ASHARE guide. [1] ................................................................ 76 2. Villot TMM validation plot [19] .......................................................................... 78 3. Measured absorption factors – different thickness ........................................... 79 viii Abstract This thesis deals with fully anechoic chamber design. The main aim of this thesis is to design fully anechoic chamber according to acoustics laws and customers (Honeywell’s) requirements. The fully anechoic chamber will be used for measuring sound and vibration quantities. This work is divided into two main parts. The first part deals with the general anechoic chamber theory and all its related design aspects. The second part, practical part, focus on specific design according to requirements. The design of the chamber was performed using advanced design methods. Key words: Sound, Vibration, Design, Anechoic chamber, Acoustics ix List of abbreviations 1D
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