Defects of Hearing
- Deterioration of hearing can occur due to
- Age
- Exposure to excessive and prolonged noise
- Genetic factors and disease
- Depending on the type of hearing loss, the response is different for different frequencies of sound
- Hearing loss due to ageing:
- Occurs at all frequencies
- With the greatest losses at higher frequencies
- Hearing loss due to excessive noise:
- Occurs in the frequency range the person was exposed to
- With the greatest loss at 4 kHz
Hearing Loss & Frequency Variation
Depending on the type of hearing loss, different responses to frequencies of sound are found to deteriorate
- The degree of hearing loss can be tested by obtaining equal loudness curves and comparing the results with the curves for normal hearing
- The same, but inverted, curve can be obtained using the dBA scale
Comparing Hearing Defects
Curve A shows the response for a young person with no hearing loss. Curve B shows the response for an older person with hearing loss due to ageing. Curve C shows the response for a young person with hearing damage due to excessive noise
Worked example
A hearing test was used to obtain threshold hearing audiograms for a group of people. The diagram below shows the audiogram obtained for a person with normal hearing.
On the graph, sketch curves to show:
(a) a curve labelled X to show a person suffering from hearing loss due to excessive noise
(b) a curve labelled Y to show a person suffering from hearing loss due to old age.
Answer:
(a) Hearing loss due to excessive noise
- Curve X: hearing loss increases up to 4 kHz then decreases after this frequency
(b) Hearing loss due to ageing
- Curve Y: loss increases as frequency increases
