Sound and the Ear


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Sound and the Ear

  1. 1. SOUND & THE EAR
  2. 2. Sound and the Ear1. Sound Waves A. Frequency: Pitch, Pure Tone. B. Intensity C. Complex Waves and Harmonic Frequencies2. The Ear A. The Outer Ear B. The Middle Ear C. The Inner Ear i. The Cochlear Membrane ii. Sound Transduction iii. Hearing Anthony J Greene Loss 2
  3. 3. Sound Waves1. Frequency• Wavelength - distance between peaks or compressions• Hertz - cycles (1 compression & 1 rarefaction) per second - the major determinant of pitch Anthony J Greene 3
  4. 4. Sound Waves• Pure Tones - simple waves• Harmonics - complex waves consisting of combinations of pure tones (Fourier analysis) - the quality of tone or its timbre (i.e. the difference between a given note on a trumpet and the same note on a violin) is given by the harmonics Anthony J Greene 4
  5. 5. Sound Waves• Pitch and fundamental frequency - in pure tones the pitch is the fundamental frequency - with harmonics added the fundamental frequency is the dominant pure tone Anthony J Greene 5
  6. 6. Sound Waves2. Intensity• Amplitude is measured in Decibels (dB)- the height of the peak, or the amount of compression - determines volume• Loudness is the psychological aspect of sound related to perceived intensity or magnitude Anthony J Greene 6
  7. 7. Sound Waves• Humans can hear across a wide range of sound intensities – Ratio between faintest and loudest sounds is more than one to one million – In order to describe differences in amplitude, sound levels are measured on a logarithmic scale, in units called decibels (dB) – Relatively small decibel changes can correspond to large physical changes (e.g., increase of 6 dB corresponds to a doubling of the amount of pressure) Anthony J Greene 7
  8. 8. Sound WavesAnthony J Greene 8
  9. 9. Direction of Sound Air MoleculesSpeaker Compression Rarefaction Anthony J Greene 9
  10. 10. Anthony J Greene 10
  11. 11. Anthony J Greene 11
  12. 12. Harmonics & Fourier Analysis Anthony J Greene 12
  13. 13. Harmonic Frequencies 1f • Strings or pipes (trombone, flute organ) 2f all have resonant1 octave frequencies. • They may vibrate at that 3f frequency or some multiple of it 4f2 octaves • All instruments and voices carry some harmonics and dampen 8f others3 octaves Length of string or pipe J Greene Anthony 13
  14. 14. Harmonic Frequencies1f + 3f + 5f + 7f + 9f + … Anthony J Greene 14
  15. 15. Harmonics & Fourier Analysis Anthony J Greene 15
  16. 16. Harmonics & Fourier AnalysisComplex sounds can bedescribed by Fourier analysis A mathematical theorem by which any sound can be divided into a set of sine waves. Combining these sine waves will reproduce the original sound. The fundamental frequency is the pitch, and the harmonic frequencies are the timbre. Results can be summarized by a spectrum Anthony J Greene 16
  17. 17. Harmonics & Fourier Analysis Anthony J Greene 17
  18. 18. TheEar Outer Ear Middle Inner Ear Ear Anthony J Greene 18
  19. 19. Outer Ear• Pinna - the fleshy part of the ear• Channels sound into the auditory canal - which carries the sound to the eardrum• tympanic membrane - vibrates in response to vibrations in the air Anthony J Greene 19
  20. 20. Middle Ear• Ossicles - the three smallest bones in the human body - malleus (hammer) incus (anvil ), stapes (stirrup ) - transmit sound to the inner ear• Eustachian tubes - connects to throat and allows air to enter the middle ear - equalizes the pressure on both sides of the eardrumConduction Deafness Anthony J Greene 20
  21. 21. Inner EarAnthony J Greene 21
  22. 22. Inner Ear1. Semi-Circular Canals2. The Cochlea• Oval Window - the connection point from the stirrup to the inner ear• Round Window Anthony J Greene 22
  23. 23. Inner Ear1. Semi-Circular Canals2. The Cochlea• Oval Window - the connection point from the stirrup to the inner ear• Round Window Anthony J Greene 23
  24. 24. Anthony J Greene 24
  25. 25. The Cochlea• Vestibular canal - wave travels from the oval window towards the end of the cochlea• Tympanic canal - wave travels from the end of the cochlea to the round window• Reissners Membrane - separates the vestibular canal from the Cochlear Duct• Basilar membrane - vibrates in response to the wave traveling around it - varies in thickness so some areas vibrate best to high pitches and some areas to low pitches• Cochlear duct -the third section of the cochlea which contains the Organ of Corti• Organ of Corti - the place where physical energy is converted to nerve energy Anthony J Greene 25
  26. 26. The CochleaAnthony J Greene 26
  27. 27. The CochleaAnthony J Greene 27
  28. 28. The CochleaAnthony J Greene 28
  29. 29. Sound Transduction• A traveling wave is set up in the vestibular canal• The wave causes the Basilar membrane to vibrate - each section is maximally stimulated by a different pitch - serves to sort out differing frequencies• In the Organ of Corti hair cells vibrate in response to the vibrations of the Basilar membrane• Hair cells transduce the energy into a neural impulse Anthony J Greene 29
  30. 30. Bassilar MembraneAnthony J Greene 30
  31. 31. Basilar Membrane Anthony J Greene 31
  32. 32. Exposure to Loud Noise Anthony J Greene 32
  33. 33. Summary Anthony J Greene 33