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While certain factors can accelerate the process, some level of hearing loss is inevitable as we age. The gradual age-related loss of hearing is called presbycusis, and according to the WHO, around a third of over-65s experience ‘disabling’ levels of hearing loss.
While we tend to think of hearing loss as simply making everything sound quieter, presbycusis affects some sounds much more than others. The lowest frequency that humans are able to detect under laboratory conditions is around 12 Hertz, whilst the highest is around 28 kilohertz. As we age, sounds at a given frequency must be louder in order for us to hear them, especially sounds at higher frequencies. For example, a sound with a frequency of 250Hz (a roll of thunder) is still audible to most 70 year-olds even if it is very quiet at 10 decibels (about as loud as normal breathing). However, to hear 4000Hz sound (about the frequency of the highest note on a piano – you can listen to 4000Hz here), most 70 year-old males would need it to be 40-50 decibels (about as loud as moderate rainfall).
Presbycusis is caused by the age related degeneration of the cochlea, within which sensory cells called hair cells encode sound waves as electrical signals that are sent to the brain, and by the loss of auditory nerve fibres which carry these signals. As visible in the above graph, hearing loss begins with the highest frequencies. At age 30, there is already a measurable increase in the hearing threshold for higher frequency sounds. With age, this spreads to lower frequencies as well.
During a normal conversation, voice frequency typically ranges from 80 to 180Hz for adult males and 165 to 255Hz for adult females. While this shouldn’t be too difficult for most elderly people to hear in a completely quiet environment, few environments are completely silent and so elderly people’s ability to hear and understand human speech is frequently impaired.
Presbycusis: An Update on Cochlear Mechanisms and Therapies: https://doi.org/10.3390/jcm9010218
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