UNIVERSITY OF CINCINNATI Date: 23-Feb-2010 I, Won Joon Song , hereby submit this original work as part of the requirements for the degree of: Doctor of Philosophy in Mechanical Engineering It is entitled: Study on Human Auditory System Models and Risk Assessment of Noise Induced Hearing Loss Student Signature: Won Joon Song This work and its defense approved by: Committee Chair: J. Kim, PhD J. Kim, PhD William Murphy, PhD William Murphy, PhD Mark Schulz, PhD Mark Schulz, PhD Teik Lim, PhD Teik Lim, PhD 3/3/2010 412 Study on Human Auditory System Models and Risk Assessment of Noise Induced Hearing Loss A dissertation submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the requirements for the degree of DOCTORATE OF PHILOSOPHY in the Department of Mechanical, Industrial and Nuclear Engineering of the College of Engineering and Applied Science 2010 By Won Joon Song B.S. Mechanical Engineering Hanyang University, Seoul, Korea, 1995 M.S. Mechanical Engineering Hanyang University, Seoul, Korea, 1997 Committee Chair: Dr. Jay H. Kim Abstract Simulation-based study of human auditory response characteristics and development of a prototype for advanced noise guideline are two major focuses of this dissertation research. This research was conducted as a part of the long-term effort to develop an improved noise guideline for better protection of the workers exposed to various noise environments. The human auditory responses were studied with simulation models. A human full-ear model derived from an existing model, Auditory Hazard Assessment Algorithm for Human (AHAAH), was utilized as a baseline for the study. Frequency- and time-domain responses of well-known human middle ear network models were cross-compared to estimate expected accuracy of the models and understand their proper use. Responses of the stapes to impulsive noises were investigated by using the middle ear models to understand the effects of the temporal characteristics of impulsive noises on the responses. Available measured transfer functions between the free-field pressure and the stapes response for human and chinchilla were also used to study the auditory response characteristics. The measured transfer functions were refined and reconditioned to make them have equivalent formats. Using the reconstructed transfer functions, time-domain stapes responses of human and chinchilla to impulsive and complex type noises were calculated and compared. Applicability of the noise metrics defined in terms of the stapes response to assess the risk of the noise induced hearing loss was studied. A prototype of an improved noise guideline was developed from existing chinchilla noise iv exposure data. Applying a new signal processing technique to the time histories of the exposed noises and studying the relationship between the noise metric and the permanent threshold shift (PTS), the dose-response relationship (DRR) was established in a compatible way with the definition used in current human noise guidelines. From the DDR, noise induced hearing loss (NIHL) threshold is estimated as a function of frequency. An advanced noise guideline that enables quantitative, frequency by frequency assessment of risk of the noise was developed by utilizing the identified NIHL threshold. The guideline was developed so that it can be easily transformed to a human noise guideline. Therefore, the guideline serves as a prototype of a future human noise guideline. v vi Acknowledgements Theory , practice , knowledge and experience, inscribed at the entrance of Swift Hall and Old Chemistry, are four elements that should be equipped to be a real engineer. I must acknowledge the dedicated efforts of Prof. Jay Kim in guiding and assisting my research. With his valuable advices and innovative suggestions, I could proceed and finalize this work. I would like to express my appreciation to Prof. Teik Lim, Prof. Mark Schulz and Dr. William Murphy for accepting to be in my dissertation committee and providing helpful review comments. My special thanks go to Drs. Price and Kalb in the U.S. Army Research Laboratory (USARL) and Drs. Hamernik and Qui in SUNY Plattsburgh for supplying useful data. The financial support by the National Institute for Occupational Safety and Health (NIOSH), Grant number R21 OH008510, is to be highly appreciated. I am deeply grateful to Shrikant Pattnaik, Steve Goley and Ed Zechmann for the friendship they showed to me. I really appreciate to my Korean friends in UC and international friends in Baldwin 445 for sharing great times with me. I wish all of them to make great strides in their future careers. I also would like to offer my special gratitude to Prof. J. K. Lim, a role model to me, in Hanyang University. My parents deserve the greatest gratitude from me. From the bottom of my heart, I appreciate the unconditional supports that I owed to my younger sisters and brother-in-law. vii Contents Introduction ............................................................................................................................................................ 1 I. Introduction to the human auditory system: Structure and functions .................................... 6 A. External ear ................................................................................................................................................ 7 B. Middle ear ................................................................................................................................................... 9 1. Tympanic membrane ......................................................................................................................... 9 2. Ossicular chain ................................................................................................................................... 11 3. Middle ear cavities ........................................................................................................................... 13 4. Eustachian tube ................................................................................................................................. 15 C. Inner ear ................................................................................................................................................... 15 II. Auditory system modeling ..................................................................................................................... 19 A. Sound source and the external ear modeling ............................................................................. 19 1. From the free-field to the concha entrance ............................................................................ 19 2. Concha and the ear canal modeling ........................................................................................... 36 B. Middle ear modeling ............................................................................................................................ 45 1. Classic configuration of the human middle ear .................................................................... 45 2. Tympanic membrane models ...................................................................................................... 50 3. Ossicular-chain and middle-ear transformer ........................................................................ 59 4. Nonlinear elements .......................................................................................................................... 72 viii 5. Stapes-cochlea (SC) complex network model ....................................................................... 87 6. Network analogues for the middle-ear cavities .................................................................. 105 C. Cochlear modeling .............................................................................................................................. 113 1. Passive cochlear model by Zwislocki (2002b) .................................................................... 113 2. Cochlear transfer function .......................................................................................................... 116 III. Comparative study of human middle ear models based on the frequency response solutions .............................................................................................................................................................. 124 A. Middle ear network models ............................................................................................................ 124 1. Classic configuration of the middle ear network model .................................................. 126 2. Selected network models for comparison ............................................................................ 128 3. Impedance characteristics of reference network models ............................................... 130 B. Middle ear transfer functions of network models .................................................................. 131 1. Pressure transfer function .......................................................................................................... 131 2. Middle-ear transfer admittance ................................................................................................ 136 3. Displacement-pressure transfer function ............................................................................. 139 4. Volume velocity transfer function ...........................................................................................