Hypersonic Sound Woody NorrisHSSDiscovery Channels Future Weapons What

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 Pressure • “Sinusoidal” wave. • Caused by vibrations of objects. • Humans can hear from 20 - 20, 000 Hz (hertz are vibrations per second). Time

Why use ultrasound? • Non-linearity occurs when systems aren’t consistent; most physical objects are nonlinear. • HSS uses frequencies of more than 60, 000 Hz because this negates sound’s natural nonlinearity. • 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 = 50 Hz. • Since humans can’t hear less than 20 Hz difference, a difference tone less than 20 Hz is perceived as volume fluctuation. • But, a difference of more than 20 Hz is heard as a 3 rd 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, 000 Hz and 60, 300 Hz gives you a 300 Hz audible tone. • Because difference tones only work in nonlinear 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 300 Hz.

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.