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15 sound

  1. 1. The Physics of Sound
  2. 2. The Nature of Sound • SOUND is a longitudinal wave that is created by vibrating objects that is capable of producing a sensation in our auditory system. • It is also called pressure wave because it consists of a series of high pressure (compression) and low pressure (rarefaction) regions. • The audible range of sound frequency for humans is from 20Hz – 20 000Hz. Sounds with frequencies below 20Hz are called infrasounds and the ones above frequencies of 20 000Hz are called ultrasounds.
  3. 3. The Speed of Sound • Since sound is a mechanical wave, then its velocity is affected by the kind of medium that it travels through. • For every phase of matter, there is a corresponding equation that describes the speed of sound. • through air: v = 331 + 0.6Tc ( Tc is temperature in C ) (in m/s)
  4. 4. Doppler Effect The apparent change in pitch due to the relative motion of the source and/or the observer.
  5. 5. Characteristic of Sound Sound may be described by 3 perceptual (as perceived by human senses – auditory) characteristics: pitch, quality, and loudness. These 3 characteristics correspond to 3 physical (scientific) characteristics: frequency, waveform, and intensity.
  6. 6. Characteristics of Sound Pitch • PITCH refers to the highness or lowness of a sound, and therefore depends on the frequency of the sounding object. It is also related to the wavelength and the energy that it carries. high pitch -- high frequency -- short waves -- high energy low pitch --- low frequency --- long waves --- low energy
  7. 7. Characteristics of Sound Loudness • This is scientifically described as sound intensity, the greater the intensity, the louder the sound, measured in decibels. ▫ Threshold of hearing – 0 db ▫ Threshold of pain – 120 db • Sound Intensity ( I ) refers to the energy the sound delivers to a unit area of a surface per unit time. ▫ Proportional to amplitude ▫ Inversely proportional to distance from source
  8. 8. Characteristics of Sound Quality • QUALITY, a.k.a. timbre, is the property of a tone that distinguishes it from another tone of the same pitch and loudness produced by a different musical instrument. • It is described by the kind of waveform that resulted from the impositions of its component frequencies.
  9. 9. Sound as a Wave • Refraction (bending) – sound bends due to temperature difference • Diffraction (scattering) –the sound wave scatters upon passing through an opening • Interference (meeting) – could be destructive or constructive e.g. noise and sound cancellation/reinforcement technology • Reflection (bouncing) – reflection of sound is called an ECHO, a series or multiple echoes is REVERBERATIONS.
  10. 10. SONAR: Sound Navigation and Ranging
  11. 11. Altimeter (Altitude Meter)

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