Hearing Impairment

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Hearing Impairment
Introduction to Acoustics

• University of Salford
• Acoustics, Audio Video Group

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Learning Outcomes

• Discuss the main types of hearing impairment
• Analyse a basic audiogram
• Explain how noise exposure can cause hearing loss

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Initial questions

• What causes hearing impairment?
• How do we measure it?
• How can we decide if a sound is likely to harm
  our hearing?

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Types of impairment
conductive
Sensori-neural
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Conductive hearing loss

• Defects in outer ear or ossicles
• Maximum loss 50 - 55 dB
• Loss roughly constant with frequency
• Examples
• perforated ear drum
• otosclerosis

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Sensorineural hearing loss

• Defect in the inner ear or connection to brain
• Loss can be complete
• Loss greater at high frequencies
• Examples
• presbycusis
• noise-induced hearing loss

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Effects on understanding speech
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Audiometry procedure

• Measures hearing threshold
• Subject wears headphones
• Send pure tone to one ear at audible level
• Decrease level until subject cant hear it
• Repeat at other (standard) frequencies
• Normal hearing (5 phon equal loudness curve) is
  called 0 dB hearing level

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Audiogram of normal hearing
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Audiogram of impaired hearing
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Noise-induced hearing loss

• What causes it?
• Which is most likely to cause damage
• 90 dBA for 8 hours
• 96 dBA for 2 hours
• 105 dBA for 15 mins?
• Which supplies the most energy?

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Noise dose

• Response to noise dose depends on the sound
  energy received
• Energy intensity x time
• How can we compare different noise doses?
• How can we evaluate the effect of a noise which
  varies over time? (tbc )

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Conclusions

• Conductive hearing loss otosclerosis, perforated
  eardrum, etc
• Sensorimeural hearing loss presbycusis, NIHL
• NIHL related to sound energy - concept of noise
  dose