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# Introduction to Acoustics (Part 1)

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### Overview

##### Class Central Tips
This course introduces acoustics by using the concept of impedance. It starts with vibrations and waves, demonstrating how vibrations can be envisaged as a kind of wave, mathematically and physically. The essential measures for acoustic waves, such as dB scale, octave scale, acoustic pressure, energy, intensity, will also be explained. These measures are realized by one-dimensional examples, which provide clear and simple physical insights.

The course then moves on to explaining waves on a flat surface of discontinuity, demonstrating how propagation characteristics of waves change in space where there is a distributed impedance mismatch. Subsequent topics are 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. In Part 1, we will handle topics from vibrations and waves to waves on a flat surface of discontinuity. The later parts will be covered in Part 2.

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 of sound and vibration concepts, are also welcome.

### Syllabus

Week 1: Vibration & Waves

• How are time and space related? What about the relation between frequency and wavelength?
• Does the characteristic impedance of medium determine reflection and transmission?
• Do we well see the waves of a string in terms of driving point impedance?

Week 2: Acoustics Wave Equation and Its Basic Physical Measures

(1D acoustic wave equation, Acoustic Intensity and Energy, Units of Sound)

• What are the relations of acoustic pressure, density, and particle velocity?
• How do they make acoustic wave equation?
• Is acoustic wave well analogous with one dimension string wave?

Week 3: Acoustics Wave Equation and Its Basic Physical Measures

(Acoustic Intensity and Energy, Solutions of the Wave equation, Demonstration: hearing system)

• What about the relation between acoustic intensity and energy?
• How does human hearing system measure sound and its characteristics?
• Let us experience the change of sound in level and frequency!

Week 4: Waves on a Flat Surface of Discontinuity

(Normal incidence on a Flat Surface, The Mass Law)

• How mathematically express the boundary conditions at discontinuity?
• How does impedance at discontinuity determine reflection and transmission?
• When can we use mass law?

Week 5: Waves on a Flat Surface of Discontinuity

(Transmission Loss, Snell’s Law, Transmission and Reflection of an Infinite Plate/Finite Structure)

• How different is the transmission loss of a flexible partition compared to the mass law?
• Does the obliqueness of wave play a critical role to determine transmitted and reflected wave?
• What are the roles of partition and fluid loading impedance to transmission loss?

Yang-Hann Kim

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