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Modern technologies in hearing aids

Modern technologies in hearing aids. Andrzej Dobrucki Institute of Telecommunications, Teleinformatics and Acoustics, Wrocław Institute of Technology Andrzej.Dobrucki@pwr.wroc.pl. Plan of presentation. Basic information about sound Elements of physiology and psychology of hearing

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Modern technologies in hearing aids

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  1. Modern technologies in hearing aids Andrzej Dobrucki Institute of Telecommunications, Teleinformatics and Acoustics, Wrocław Institute of Technology Andrzej.Dobrucki@pwr.wroc.pl

  2. Plan of presentation • Basic information about sound • Elements of physiology and psychology of hearing • Hearing impairments • Technology of hearing aids • Fitting of hearing aids • Cochlear implants

  3. Sound • Acoustic pressure • Particle (acoustic) velocity • Sound (wave) speed • Sound intensity

  4. Acoustic pressure p – acoustic pressure P – instantanenous (total) pressure P0 – static (atmospheric) pressure P0 = 105 Pa (1 Pa=1 N/m2) The lowest value of acoustic pressure detected by human auditory system (Threshold of hearing): 20 mPa (0.00002 Pa) Threshold of pain: 63.2 Pa

  5. Acoustic velocity The velocity of vibration of medium particles The smallest audible value of acoustic velocity: ca. 5·10-8 m/s Threshold of pain: 0.15 m/s Acoustic impedance: For plane wave:

  6. Speed of sound Depends only on medium and absolute temperature: R – universal gas constant g– ratio of characteristic heats: for constant pressure and constant volume m – molecular mass T – absolute temperature, in kelvins In air: T=0oC (273 K), c=331 m/s T=20oC (293 K), c=344 m/s

  7. Sound intensity Energy of sound, flowing in the time unit through unit surface, perpendicularly to it Threshold of hearing: I0=10-12 W/m2 Threshold of pain: Imax=10W/m2

  8. Weber-Fechner law

  9. Levels and decibels Intensity level: where: I0=10-12 W/m2, threshold of hearing where:p0=20 mPa, threshold of hearing Lp – sound pressure level Unit of level (intensity or SPL) – decibel [dB]

  10. Levels

  11. Dependence of loudness level on frequency Intensity level Frequency

  12. A - weighting

  13. Typical A-weighted levels

  14. Human auditory system • Peripheries (the ear) • Central auditory system

  15. The ear

  16. Outer ear • Pinna • Canal • Eardrum

  17. Functions of outer ear • Localization of the sound source • Protection of eardrum • Amplification of sound (selective)

  18. Middle ear • Middle-ear cavity • Ossicular chain (malleus, incus, stapes) • Muscles (stapedius muscle, tensor tympani muscle) • Eustachian tube

  19. Middle ear

  20. Functions of middle ear • Fitting of acoustical impedance • Protection against high sound level • Equalization of static pressures between outer and middle ear

  21. Fitting of acoustical impedance • Effect of lever • Effect of piston

  22. Inner ear • Semicircural canals (equilibrium sensor) • Cochlea and auditory nerve

  23. Cochlea

  24. Cochlea

  25. Organ of Corti

  26. Cochlea

  27. Selectivity of hearing

  28. Ascending auditory pathway

  29. Descending auditory pathway

  30. Auditory area

  31. Hearing loss

  32. Types of hearing impairments • Conductive hearing loss • Sensorineural hearing loss • Sensorineural (extracochlear) • Mixed hearing loss

  33. Classification of severity of hearing loss Threshold (dB HL) Classification -10 - 25 Normal 26 - 40 Mild 41 - 55 Moderate 56 – 70 Moderately-severe 71 – 90 Severe > 90 Profound

  34. Diagnosis of hearing impairment • Audiometrical methods (the cooperation of patient necessary) • Objective methods (the cooperation unnecessary)

  35. Pure tone audiometry • Air conduction • Bone conduction

  36. Audiograms

  37. Loudness recruitment

  38. Speech audiometry

  39. Tympanometry

  40. Tympanogram

  41. Otoacoustic emission

  42. Hearing cells (outer) Normal Damaged

  43. Auditory Brainstem Response

  44. Hearing aids • Behind the ear (BTE) • Inside the ear (ITE) • Inside the canal (ITC)

  45. Hearing aids BTE

  46. Advantages: Easy for maintenance Easy for fitting to each kind of hearing loss Economical in use (low cost batteries, low power consumption) Possibility of use additional accesories Disadvantages Relatively large size Unsatisfied cosmetical effect Hearing aids BTE

  47. Hearing aids ITE

  48. Advantages Better cosmetical effect Economical in use Easy for manual maintenance Disadvantages Limitation connected with anatomy of outer ear Not applicable for severe hear impairments For some persons still unsatisfied cosmetical effect Hearing aids ITE

  49. Hearing aids ITC

  50. Advantages Ideal cosmetic effect Disadvantages Requires high precision in maintenance Reqiures frequent cleaning Only for mild hearing loss Not economical in use Strong limitation connected with anatomy of outer ear Hearing aids ITC

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