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Acoustics

Explore the fascinating world of acoustics through the properties of sound. Discover how sound waves are created when objects vibrate, and how they travel through different mediums like air, water, and solids. Engage in hands-on experiments, such as plucking rubber bands to observe string vibrations and learn about harmonics and fundamental frequencies. Understand how these concepts apply to musical instruments, and uncover the secrets behind how sound is perceived and measured. Dive into the harmonic series and learn how they contribute to the richness of musical tones.

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Acoustics

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  1. Acoustics

  2. Acoustics:The Properties of Sound • air pressure changes when objects vibrate, producing sound in the ear • pound a table • pluck a string

  3. Sound Waves • vibrations are transmitted to our ears by a medium — usually air • sound waves radiate through air outward from the source sound like <W1:28>waves in water that radiate in circles from a tossed pebble

  4. Sound Waves • sound waves also radiate through water and solid materials, such as doors • listen to underwater sounds in the swimming pool! • get a friend to hum underwater • how far away can you hear the sound?

  5. Vibrating String

  6. String Vibrations • rubber band experiment • hold both ends of a rubber band • have a partner pluck the rubber band • notice the movement of the rubber band • the whole length is vibrating

  7. String Vibrations • strings and pipes vibrate in segments of their length, as well as in their entirety — at the same time • fundamental • frequency produced by vibration of total length • usually loudest frequency produced

  8. String Vibrations • harmonics • exact whole-number multiples of fundamental • proportion of string is reciprocal of frequency string length = f = fundamental frequency 1/2 string length = 2f 1/3 string length = 3f 1/4 string length = 4f • [i:30] harmonics on sanxian

  9. Harmonic Series • harmonic series • a series of harmonics or partials above a given pitch • harmonic partials • occur at integer multiples of the fundamental • wind and string instruments • example: if the frequency of C= 64 Hertz, the frequency of the 2nd partial is 2 * 64 = 128 Hertz

  10. Harmonics • <w1:29>pipes like the flute have harmonics

  11. Harmonic Series • The French horn also has harmonic partials – live demo

  12. How Does Sound Work? • Many musical sounds are made of special combinations of harmonics

  13. How Loud Are the Harmonics? • Here is a graph of the first 15 harmonics of a [i:31] vocal tone

  14. How Loud Are the Harmonics? • Here is the average loudness of the same [i:31] vocal tone

  15. How Loud Are the Harmonics? • The vocal tone's first harmonic fades in and out like this:

  16. How Steady is the Sound? • The vocal tone's frequency moves up and down this:

  17. Harmonic Series • Using its harmonic pattern , we can recreate a [i:32] vocal tone

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