1. 17.4
Sound and Hearing

2. Sound Waves
Longitudinal waves

3. Properties of Sound Waves
Speed
Intensity & loudness
Frequency & Pitch

4. At 200C the speed of sound is 342 m/s

5. Varies based on the medium (phase & temp.) Fastest in solids
Speed
Varies based on the medium (phase & temp.)
Fastest in solids
Depends on density and elasticity of medium

6. Intensity and loudness
Intensity = rate wave’s energy flows through area

7. Intensity and loudness
Depends on amplitude and distance from source

8. Which wave is the loudest?

9. Measured in decibels (dB)
Intensity
Measured in decibels (dB)
0 dB = barely can be heard
15-20 dB = whisper
40-50 = normal conversation
120 = threshold of pain in humans
= jet engine taking off

11. Physical response to intensity Varies based on physical factors
Loudness
Physical response to intensity
Varies based on physical factors

12. As intensity increases, loudness increases.

13. Pitch is frequency as you perceive it.
Frequency & Pitch
Pitch is frequency as you perceive it.
Remember: long wavelength = low frequency

14. High frequency sounds have a high pitch.
Frequency & Pitch
High frequency sounds have a high pitch.
Low frequency sounds have a low pitch.

15. Which wave has the highest pitch?

16. Which wave is the loudest? Which wave has the highest pitch?

17. Sound
People can hear between 20 and 20,000 Hz.
Infrasound is lower than people can hear.
Ultrasound is higher than people can hear.

18. Used in sonar and ultrasound imaging.
Sonar- determines distance to an object underwater

19. Ultrasound Ultrasound imaging
Most people hear sounds between 20 Hz and 20,000 Hz.
Infrasound- sound at frequencies below what people can hear.
Ultrasound is higher than what people can hear.
Sonar- technique for determining the distance to an object under water.
Ultrasound imaging

20. Ultrasound Imaging Ultrasound pulses are sent into a patient
Each pulse is short (1/8000 second)
Pulses are too short for the reflection to interfere with the next pulse
Reflected pulses make a detailed map of structures/organs inside the body

21. Ultrasound Imaging

22. Fetal Ultrasound
Face

23. Kidney Ultrasound

24. Heart Ultrasound

25. Change in frequency caused by motion of the source, listener, or both.
Doppler Effect
Change in frequency caused by motion of the source, listener, or both.

26. The Doppler Effect

27. Higher frequency when approaching Lower frequency when moving away
Doppler Effect
Higher frequency when approaching
Lower frequency when moving away

30. The Ear
3 parts:
Outer
Middle
Inner

31. Parts of the Ear

32. Gathers and focuses sound into middle ear About 2.5 cm long
Outer Ear
Gathers and focuses sound into middle ear
About 2.5 cm long

33. Outer Ear

34. Receives and amplifies sound vibrations Contains 3 bones:
Middle Ear
Receives and amplifies sound vibrations
Contains 3 bones:
Hammer, anvil, & stirrup

35. Middle Ear

36. Inner Ear
Uses nerve endings to sense vibrations and send signals to the brain
Made up of the cochlea- spiral shaped canal filled with fluid and lined by thousands of nerve cells with tiny hair-like projections

37. Inner Ear

39. Hearing Sound is funneled by the outer ear It hits the eardrum
The eardrum vibrates at the same frequency as the sound waves hitting it.
The vibration is transferred to the hammer
The hammer hits the anvil
The anvil moves the stirrup back and forth
Vibrations then enter the cochlea

40. Hearing The hair-like projections in the cochlea sense vibrations
The nerve cells send electrical impulses to the brain

41. Reproducing Sound
Sound waves are converted into electronic signals that can be processed and stored.
To hear the sound, the electronic signals are converted back into sound waves.

42. Recreating Sound
Electronic signals vibrate a magnet that is attached to a membrane.
The membrane sends sound waves through the air.
The reverse process is used to record sound.

44. Resonance
Response of a standing wave to another wave of the same frequency
Depends on interference (constructive or destructive)