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More On Sound

More On Sound. Quality. How you can tell one sound source from another even when playing the same frequency Depends on the presence of overtones. Tuning Fork Guitar. Noise. Unpleasant combo of overtones. Sound Interference.

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More On Sound

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  1. More On Sound

  2. Quality • How you can tell one sound source from another even when playing the same frequency • Depends on the presence of overtones

  3. Tuning Fork Guitar

  4. Noise • Unpleasant combo of overtones

  5. Sound Interference • When sound waves travel through the same space, they interfere with one another • In some places they interfere constructively and the sound intensity is amplified • In some places they interfere destructively and intensity is decreased • Constructive interference occurs every whole wavelength while destructive interference occurs every ½ wavelength

  6. Beat • When two sounds are close in frequency they can interfere with one another over time • You will hear alternating loud and and soft sounds

  7. Beat Frequency • Number of loud sounds heard per second B =  f2 – f1 • Human ear can only detect beat frequencies less than 7 Hz (difference in frequency of 7 Hz) • Used to tune instuments

  8. Example • A tuning fork produces a steady 400Hz tone. When struck and held near a guitar string twenty beats are counted in 5 seconds. What are the possible frequencies of the guitar string?

  9. Mach • Supersonic Speed – faster than sound • Mach – ratio of speed of an object to the speed of sound Mach = speed/ speed of sound

  10. Example • What is the speed of a plane traveling at Mach 3?

  11. Sonic Boom • When an object approaches the speed of sound, circular wave fronts pile up in front • At point of pile up, air pressure is high – called the Sound Barrier (lots of turbulance) • Once past the sound barrier, wave fronts pile up along the side • Constructive interference creates high pressure area which sweeps the ground – Sonic Boom

  12. Doppler Effect

  13. What Is It? • Pitch of an object appears to change as it passes a stationary observer • In front of moving object, waves pile up creating area of higher frequency • Behind waves spread out, lower frequency

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