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The Nature of Sound Wave

The Nature of Sound Wave . Recall: A wave is a disturbance that travels through a medium,  transporting energy from one location to another location. The medium is simply the material through which the disturbance is moving; it can be thought of as a series of interacting particles.

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The Nature of Sound Wave

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  1. The Nature of Sound Wave

  2. Recall: • A wave is a disturbance that travels through a medium, transporting energy from one location to another location. • The medium is simply the material through which the disturbance is moving; it can be thought of as a series of interacting particles

  3. Sound is a Mechanical Wave A sound wave is similar in nature to a slinky wave for a variety of reasons: • there is a medium that carries the disturbance from one location to another. Ex. Air, water, steel, etc • there is an original source of the wave, some vibrating object capable of disturbing the first particle of the medium

  4. the disturbance could be created by the vibrating vocal cords of a person, the vibrating string and soundboard of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker • the sound wave is transported from one location to another by means of particle-to-particle interaction.

  5. Since a sound wave is a disturbance that is transported through a medium via the mechanism of particle-to-particle interaction, a sound wave is characterized as a mechanical wave.

  6. A sound wave is different than a light wave in that a sound wave is • produced by an oscillating object and a light wave is not. • not capable of traveling through a vacuum. • not capable of diffracting and a light wave is. • capable of existing with a variety of frequencies and a light wave has a single frequency.

  7. Sound as a Longitudinal Wave • Longitudinal waves are waves in which the motion of the individual particles of the medium is in a direction that is parallel to the direction of energy transport • Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves

  8. The result of such longitudinal vibrations is the creation of Compressions and rarefactions within the air. • Compressions are regions of high air pressure • Rarefactionsare regions of low air pressure

  9. The wavelength of a wave is merely the distance that a disturbance travels along the medium in one complete wave cycle • Longitudinal wave does not contain crests and troughs, its wavelength must be measured differently • The wavelength is commonly measured as the distance from one compression to the next adjacent compression or the distance from one rarefaction to the next adjacent rarefaction.

  10. Sound as Pressure Wave • a sound wave consists of a repeating pattern of high-pressure and low-pressure regions moving through a medium • If a detector, whether it is the human ear or a man-made instrument, were used to detect a sound wave, it would detect fluctuations in pressure as the sound wave impinges upon the detecting device

  11. pressure versus time

  12. Pitch and Frequency • The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium.  • The frequency of a wave is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time.  1 Hertz = 1 vibration/second

  13. the period of the sound wave can be found by measuring the time between successive high pressure points (corresponding to the compressions) or the time between successive low pressure points (corresponding to the rarefactions)

  14. The human ear is capable of detecting sound waves with a wide range of frequencies, • ranging between approximately 20 Hz to 20 000 Hz • Infrasound - any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) • Ultrasound - any sound with a frequency above the audible range of hearing (i.e., more than 20 000 Hz)

  15. Dogs can detect frequencies as low as approximately 50 Hz and as high as 45 000 Hz. • Cats can detect frequencies as low as approximately 45 Hz and as high as 85 000 Hz. • Bats can detect frequencies as high as 120 000 Hz • Dolphins can detect frequencies as high as 200 000 Hz • An elephant possesses the unusual ability to detect infrasound, having an audible range from approximately 5 Hz to approximately 10 000 Hz.

  16. The sensation of a frequency is commonly referred to as the PITCH of a sound. • A high pitch sound corresponds to a high frequency sound wave • A low pitch sound corresponds to a low frequency sound wave

  17. Intensity and Decibel • Sound waves are introduced into a medium by the vibration of an object • The disturbance then travels from particle to particle through the medium, transporting energy as it moves. • The amount of energy that is transferred to the medium is dependent upon the amplitude of vibrations • The amount of energy that is transported past a given area of the medium per unit of time is known as the Intensity ofthe sound wave

  18. The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is.

  19. Intensity Typical units for expressing the intensity of a sound wave are Watts/meter2

  20. The faintest sound that the typical human ear can detect has an intensity of 1X10-12W/m2 • A sound with an intensity of 1X10-12 W/m2 corresponds to a sound that will displace particles of air by a mere one-billionth of a centimeter. • This faintest sound that a human ear can detect is known as the threshold of hearing

  21. Since the range of intensities that the human ear can detect is so large, the scale that is frequently used by physicists to measure intensity is a scale based on multiples of 10. • This type of scale is sometimes referred to as a logarithmic scale. The scale for measuring intensity is the decibel scale.

  22. Sound Intensity Level • I is the intensity of the sound • Io is the reference intensity • Io = 1X10-12 W/m2

  23. Terms used in description of Sound • Loudness for a given frequency, the greater the pressure amplitude, the louder the sound a listener will perceive. • Pitch for a given sound wave, the greater the frequency, the higher the pitch • Timbre – difference in sound waves caused by the difference in harmonic content clarinet tone – rich in harmonic (more reedy) alto record tone – mostly fundamentals (more mellow)

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