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Sensory presbycusis: This refers to epithelial atrophy with loss of sensory hair cells and supporting cells in the organ of Corti. Mechanical (ie, cochlear conductive) presbycusis: This condition results from thickening and secondary stiffening of the basilar membrane of the cochlea. The rest of my answer is based on this book, some parts of which exist online (which I'll quote). As you can see from the graph, severity of age-related hearing loss depends on sound frequency: older people need high-pitched sounds to be displayed more loudly, in order to hear them.
It's not described much on the website, but the book explains that there is a relationship between how loud a sound has to be to harm you, and which frequency it is.
Here's a plot of the connection between loudness and frequency in auditory perception, in which you can see that sounds around 4kHz can most easily harm us.
Does this explain that when I was younger, I was more sensitive to sound and slept less well? Not the answer you're looking for?Browse other questions tagged medical-science or ask your own question.
Is making characters who go off the rails unlucky a good technique for keeping the plot moving? Contact us A» Professionals A» Telecom A» Main Siteabout the projectTelecommunicationsWith the liberalization of the telephone market, telecommunication network vendors are not highly restricted to standards, unlike the previous state-run networks used to be. The first listening test results indicate that hearing impaired listeners judge the overall quality of degraded speech less critically than normal hearing listeners.
Characteristically, presbycusis involves bilateral high-frequency hearing loss associated with difficulty in speech discrimination and central auditory processing of information. This process originates in the basal turn of the cochlea and slowly progresses toward the apex. The thickening is more severe in the basal turn of the cochlea where the basilar membrane is narrow.

The question is being unable to hear ranges as we get older, starting from childhood, while presbycusis is specific to post middle-aged people. Sounds that are near our auditory thresholds (under 20 Hz and above 20.000 Hz in the normal, healthy hearing range) can't harm us even if they are extremely loud.
With the introduction of Voice over Internet Protocol (VoIP) telecom services, the situation became worse, as many new standards were introduced and compatibility between networks (plain old telephone system, POTS, integrated service digital network, ISDN, mobile networks and VoIP networks) still remains an issue. The hearing aid gives benefit to too soft loudness or it may give benefit to certain codec or VoIP telephone transmissions. These changes correlate with a precipitous drop in the high-frequency thresholds, which begins after middle age. This correlates with a gradually sloping high-frequency sensorineural hearing loss that is slowly progressive. The wiki page does refer to the issue as presbycusis, yet every reliable source on presbycusis lists it as being limited to post middle-aged people.
We don't hear them because they cause no mechanical change in our ear that responds to those frequencies, and consequently no harm is done. Together with traditional technical disturbances like noise or echo, new disturbances or impairments - like different encoding-decoding algorithms (codecs), packet loss or bit error rates - come with the new telephone network technology.
The abrupt downward slope of the audiogram begins above the speech frequencies; therefore, speech discrimination is often preserved. It seems the wiki page is the only source referring to range of audible frequencies in young people as presbycusis?
In the case of age-related hearing loss, the hair cells in the inner ear that should respond to high-frequency sounds, have already stopped responding, so there is nothing left to harm. These telephone transmission disturbances have been tested in the past with a wide range of tests for normal hearing users. Histologically, the atrophy may be limited to only the first few millimeters of the basal end of the cochlea.

So far there are only few tests available with regard to the new network technology and new telephone transmission disturbances for hearing impaired users. We shortly describe what kind of old and new telephone transmission disturbances will appear on modern networks.Already the transmission quality of POTS was sensitive to a wide range of telephone transmission disturbances. One theory proposes that these changes are due to the accumulation of lipofuscin pigment granules.
The main effects on the transmission line were band limitation of 300 Hz - 3400 Hz, circuit noise caused by transmission line amplifiers, too loud or too soft loudness caused by badly chosen amplification factors, delays caused by long transmission lines and echoes caused by insufficient transmission line termination. With the introduction of digital network components, codecs became an essential part of the transmission system, going along with codec distortions. The last major step in telephone transmission systems so far was the packet assembly of the so far continuous data stream. In Proceedings of the Conference on Assistive Technology for Vision and Hearing Impairments, Kufstein, Austria, 2006. This buffer allows data packages to arrive a bit earlier or a bit later than the mean data package would. The jitter buffer costs time and in case a package is too late, it means this data package will be lost and has to be replaced. In parallel to the new telephone transmission disturbances, the design of new telephone handsets comes with new telephone disturbances, like worse signal-to-noise ratio (speech-to-environmental noise ratio), not optimized listener side tone, additional codecs and echoes.
All these telephone situation related disturbances can be drawn into a schema as shown in Figure 1.

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