Introduction to Acoustics (Part 2)

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Course Date: 11 August 2014 to 15 September 2014 (5 weeks)

Price: free

Course Summary

Learn about acoustics by using the concept of impedance. Following part 1, radiation, scattering, and diffraction are studied. Wave propagation in closed space is also covered. Leads to understand essentials as well to cover graduate level topics.

Estimated Workload: 3-6 hours/week

Course Instructors

Yang-Hann Kim

The research area of professor Yang-Hann Kim is mainly acoustics, noise/vibration. Experimental approaches and associated digital signal processing are used the most. Research projects include sound field visualization, noise source identification using array microphone, detection and estimation of moving noise source, structural acoustics, duct acoustics, silencer design, diagnostics of machines, and active noise/vibration control. Recently, he has been recognized as a pioneer in the field of sound visualization and manipulation. The latter is to make any sound field or shape in the selected region/regions. Therefore, it can be used for having very focused sound field, private sound zone/zones, or 3D listening field.

He joined the Department of Mechanical Engineering as an Associate Professor in 1989. Previously he worked for five years at the Korea Institute of Technology as an Assistant and Associate Professor of the Department of Mechatronics. From 1979 to 1984, he was a research assistant at the Acoustics and Vibration Laboratory of Massachusetts Institute of Technology while pursuing Ph.D. degree in the field of acoustic and vibration, and obtained Ph.D. in February 1985 at M.I.T., Mechanical Engineering (O.E. Program).

He has been on the editorial board of Mechanical Systems and Signal Processing (MSSP), editorial advisor of the Journal of Sound and Vibration (JSV) and Journal of Noise Control Engineering. He also served KSNVE as an editor for three years (1995 - 97). His research has been recognized in the professional societies and institutes in many respects, including the bet paper award by KSNVE (1998), the best research award by ASK (1997), second place award in the sound visualization competition by the Acoustical Society of America (1997), the best international cooperation award from KAIST, and KSNVE, and the best teaching award from KAIST, department of M.E (2010). He is elected as co-chairman of inter-noise 2015, San Francisco, also a director of I-INCE. He is a Fellow of the Acoustical Society of America. He is also an editor of Noise Control Engineering Journal(NCEJ), starting from Sept. of 2014.

He has published more than 100 papers, mostly in the field of sound visualization and manipulation, in the well-known journals, including the Journal of the Acoustical Society of America, Journal of Sound and Vibration, and Journal of Acoustics and Vibration, the Transaction of ASME. He is an author of well-known acoustics texts, Sound Propagation: An Impedance Based Approach and Sound Visualization and Manipulation (coauthored with Jung-Woo Choi), published by John Wiley & Sons, Inc. He also wrote the chapter “Acoustic holography” in the Handbook of Acoustics, published by Springer Verlag.

Course Description

This course introduces acoustics by using the concept of impedance. In the previous part, the course starts with vibrations and waves, demonstrating how vibration can be envisaged as a kind of wave, mathematically and physically. They are realized by one-dimensional examples, which provide mathematically simplest but clear enough physical insights. Then the part 1 ends with explaining waves on a flat surface of discontinuity, demonstrating how propagation characteristics of waves change in space where there is a distributed impedance mismatch. 
Following the part 1, part 2 starts with radiation, scattering, and diffraction, which can be explained in a unified way by seeing the changes of waves due to spatially distributed impedance. Lastly, the course covers sound in closed space, which is considered to be a space that is surrounded by spatially distributed impedance, and introduces two spaces: acoustically large and small space. 
This course is for graduate students and advanced undergraduates in acoustics, audio engineering, and noise control engineering. Practicing engineers and researchers in audio engineering and noise control, or students in engineering and physics disciplines, who want to gain an understanding sound and vibration concepts, are also welcome. For the continuity of the lecture, taking part 1 of the course is recommended (but not required). 


Will I get a Statement of Accomplishment after completing this class? 

Yes. Students who successfully complete the class will receive a Statement of Accomplishment signed by the instructor. The final grade is based on 4 quizzes (80% of the final grade) and a final exam (20% of the final grade). To receive a Statement of Accomplishment, you have to obtain more than 60% of the maximum score. To receive a Statement of Accomplishment with Distinction, you have to obtain more than 80% of the maximum score.

What is the coolest thing I'll learn if I take this class? 

Acoustics is one of the most complicated studies, which needs a lot of mathematical formulation. For the beginners, this course offers a less mathematically-intensive means to understand a subject matter, which provides an excellent launching point for more advanced study. For the experts, this course gives a chance to review the basics, by using the concept of impedance.


Week 1. Radiation – Breathing & Trembling Sphere Problem

What happens if we have a certain discontinuity that is a function of three spatial variables (e.g. x,y,z for Cartesian coordinate)?

- What are the radiation characteristics of a breathing sphere, which is assumed to vibrate omni-directionally with equal magnitude?

What is the difference between a breathing sphere and a trembling sphere, which vibrates in a certain direction with a uniform velocity?

Week 2. Radiation – Baffled Piston & Finite Vibrating Plate Problem

How can we generate sound? By the fluctuation of fluid particles or the vibration of structures? How are they related?

How can we understand the radiation of a finite vibrating plate? Can we assume this plate as numerous vibrating pistons?

 Week 3. Scattering & Diffraction / Kirchhoff-Helmholtz Equation

How can we express the wave propagation when it is reflected due to the presence of discontinuities in space?

How can we explain the circumstances under which we can hear sound but cannot see the sound source?

What is the relation between the wavelength and the diffraction?

Week 4. Wave Propagation in Space / Reverberation Period and its Design Application

If there are different types of impedance distribution in space, how can we explain the propagation characteristics?

How can we acoustically define ‘large’ or ‘small’ space’? Is it related to the frequency?

Is there any measure that can represent the characteristics of the space?

Week 5. Wave Propagation in Space / Duct Acoustics

How can we express the sound field that is neither fully diffuse field nor only a direct field?

When the size of the space is small relative to wavelength, what happens to the propagation of sound?

When the length of one direction is significantly greater than the cross-sectional direction of the space, how does the wave propagate with respect to its wavelength?


The class will consist of 1 introduction video and 6 lecture videos per week, each of them is about 20 minutes in length. There will be a quiz every week, and a final exam at the final week. Lecture PPT files are available in the course. 

Suggested Reading

Although the lectures are designed to be self-contained, we recommend (but do not require) that students refer to the book "Sound Propagation: An Impedance Based Approach (Wiley & Sons, 2010) Written by the instructor, Yang-Hann Kim. Chapter 4 and 5 covers the topics that are dealt in part 2.

Course Workload

3-6 hours/week

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