Sound and Hearing

1
Sound and Hearing
2
Sound Waves

• Sound waves are mechanical and longitudinal waves
• What does this tell you about sound waves?

Sound waves need a material (medium) to travel
through Sound waves travel as a series of
compressions and rarefactions
3
Properties of SoundSpeed

• In air at room temperature, sound travels around
  340 m/s
• About 765 mi/hr
• Sound generally travels fastest in solids and
  slowest in gases. Why?

4
Particles collide most often energy is
transferred the fastest
Particles collide least often energy is
transferred the slowest
5
Properties of SoundSpeed

• In air at room temperature, sound travels around
  340 m/s
• Sound generally travels fastest in solids and
  slowest in gases. Why?
• Sound will also travel faster in materials as the
  temperature of a substance increases. Why?

6
As the temperature of a substance increases, the
speed of the particles increases, so particles
(of any state of matter) collide more often, so
energy is transferred faster
7
Properties of SoundIntensity ( Volume)

• Intensity is the rate that energy flows through a
  given area
• Rate a measurement over a specific period of
  time or per time
• What area are people most concerned with?
• Intensity depends on the waves amplitude and
  distance from the sound source
• Why?
• Measured in decibels (dB)

8
Properties of SoundPitch

• What a wave sounds like to a person
• Pitch is based on the frequency of the wave
• High frequency high pitch
• Low frequency low pitch
• Pitch (how a sound is perceived by an individual)
  depends on factors like age, health, previous
  damage, heredity

9
Ultrasound

• Waves at frequencies higher than most humans can
  hear
• Generally gt20,000 Hz
• Applications for Ultrasound Waves
• Sonar technique for determining the distance to
  an object through water
• Imaging Looking at reflected waves and based on
  the reflections, a detailed picture of an object
  can be produced

10
Doppler Effect

• A change in the frequency of a wave caused by the
  motion of a sound source or the motion of the
  listener (or both)
• As the distance between the source and the
  listener decreases, pitch increases
• As the distance between the source and the
  listener increases, pitch decreases

11
Sound and Music

• Musical Instruments vary the frequency of the
  waves it produces by changing the wavelength of
  standing waves
• Resonance Sound waves cause other items to
  vibrate, which greatly increases the amplitude of
  the waves produced, which increases the volume

12
Hearing and the Structure of the Ear

• Outer Ear Funnels sound down ear canal waves
  strike eardrum and eardrum vibrates at same
  frequency as wave
• Middle Ear contains three bones (hammer, anvil,
  stirrup) that act as amplifiers
• Inner Ear Tiny, hair-like projections send
  electrical impulse through nerves to the brain

13
Recording Reproducing Sound

• Sound is recorded by converting sound waves into
  electrical signals that can be processed and
  stored
• Sound is reproduced by converting electrical
  signals back into mechanical, longitudinal waves
  (using a speaker)

14
Changing the Wavelength