Hypersonic Sound

• Woody Norris-HSS-Discovery Channel's "Future Weapons"

What is HSS?

• Allows you to direct sound into a narrow beam.

• Sound travels hundreds of yards without experiencing attenuation.

• Does this by manipulating inaudible ultrasound.

• Open light bulb flash light.

Sound Waves

• “Sinusoidal” wave.

• Caused by vibrations of objects.

• Humans can hear from 20 - 20,000Hz (hertz are vibrations per second).

Time

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Why use ultrasound?

• Non-linearity occurs when systems aren’t consistent; most physical objects are non-linear.

• HSS uses frequencies of more than 60,000Hz because this negates sound’s natural non-linearity.

• This allows HSS to travel long distances and remain focused without attenuating.

• When HSS hits a non-linear object (like your ear or a wall), it resounds.

Difference/Tartini Tones

• Caused by tones with slightly different frequencies.

• Perceived as fluctuations in volume.

• Only works in a non-linear system.

Piecing it Together

• With difference tones, the tone that you hear is the difference in Hz of the 2 tones being played. i.e: 400 + 401 = 1 Hz… 400 + 450 = 50Hz.

• Since humans can’t hear less than 20Hz difference, a difference tone less than 20Hz is perceived as volume fluctuation.

• But, a difference of more than 20Hz is heard as a 3rd tone being played simultaneous to the first 2 tones.

Ultrasound + Difference Tone = Sound

• Even though the 2 tones are ultrasonic, you can still produce difference tones.

• i.e. 60,000Hz and 60,300Hz gives you a 300Hz audible tone.

• Because difference tones only work in non-linear systems, you only hear the tone when it hits your ear, the wall, or some other object.

• Since the first two tones are inaudible, however, you only hear the difference tone of 300Hz.

Practical Uses

• Advertising displays

• Military NRAD technology

• Performance halls and theaters

• Car stereo systems

• Computer speakers

• Guerilla military strikes

• Classrooms

Extensions into Music

• Because acoustic instruments--and your ears--are non-linear, difference tones (in music Tartini tones) are present.

• Since no tones in music are ultrasonic, all 3 tones are evident… not just the two being played or the one Tartini tone.

• How does this affect our perception of intervals and harmony?

• How does this affect consonance and dissonance?

Annotated Resources

• Feynman, Richard P., Robert B. Leighton, and Matthew Sands. The Feynman Lectures on Physics. Reading, Mass.: Addison-Wesley, 1963.Chapter 47 of this book explores the topic of sound waves and eventually their relation to electromagnetic waves and atomic harmonics. Equations are given in calculus format.

• Kock, Winston E. Sound Waves and Light Waves. Garden City, NY: Anchor Books, 1965.This book provides the fundamentals of sound- and light-wave motion and delves into the topic of propagation and dissipation of waves.

• Levitin, Daniel J. This Is Your Brain on Music : The Science of a Human Obsession. New York: Plume, 2007.This is an excellent book about how the brain processes music and sound. In addition, a section of the book is devoted to explaining the basics of music notation and jargon.

Online Resources

• Wikipedia article on HSS.• University of New South Wales' physics

page--an excellent resource.• Woody Norris demonstrating HSS.• PDF document explaining attenuation in

greater depth.• Woody Norris's TEDtalks presentation of

HSS.