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  1. I wonder if there is scientific foundation on decreasing frequency of sound we can hear as we age, as indicated on this website http://www.freemosquitoringtones.org/.
  2. What about the lowest frequency we can hear?
  3. Does that mean high frequency sound become less harmful as we become older and older?

Some side questions:

  1. Does this explain that when I was younger, I was more sensitive to sound and slept less well?
  2. Does this fact indicate some trend of our change of music taste over the time?
  • I've seen a demonstration of this in a lecture hall by show of hands. It's really quite interesting (and unfortunate). It's not definitively established why high-frequency neurons die, but they appear to be more sensitive to sound-induced damage (excitotoxicity? mechanical stress?...hard to tell). – Rex Kerr Mar 19 '12 at 7:02
  • @tim I've altered the title slightly. Hope that's OK. – matt_black Mar 21 '12 at 22:19
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It's a well-known disease/condition, medically known as presbycusis:

The term presbycusis refers to sensorineural hearing impairment in elderly individuals. Characteristically, presbycusis involves bilateral high-frequency hearing loss associated with difficulty in speech discrimination and central auditory processing of information.

The disease is well studied and there are four known factors, two of which are related to the loss of high frequencies:

Sensory presbycusis: This refers to epithelial atrophy with loss of sensory hair cells and supporting cells in the organ of Corti. This process originates in the basal turn of the cochlea and slowly progresses toward the apex. These changes correlate with a precipitous drop in the high-frequency thresholds, which begins after middle age. The abrupt downward slope of the audiogram begins above the speech frequencies; therefore, speech discrimination is often preserved. Histologically, the atrophy may be limited to only the first few millimeters of the basal end of the cochlea. The process is slowly progressive over time. One theory proposes that these changes are due to the accumulation of lipofuscin pigment granules.

[...]

Mechanical (ie, cochlear conductive) presbycusis: This condition results from thickening and secondary stiffening of the basilar membrane of the cochlea. The thickening is more severe in the basal turn of the cochlea where the basilar membrane is narrow. This correlates with a gradually sloping high-frequency sensorineural hearing loss that is slowly progressive. Speech discrimination is average for the given pure-tone average.

Source

There is a full ISO specification (ISO 7029) which describe exactly the amount of hearing loss (up to 8 kHz) starting from age 20:

hearing loss table

  • Thanks! (1) What about the lowest frequency we can hear? (2) Does that mean high frequency sound become less harmful as we become older and older? – Tim Mar 17 '12 at 21:45
  • @Tim (1) We lose all frequencies (we tend to become deaf) but higher frequencies in particular. We still lose low frequencies as well. (2) Frequencies are not particularly "harmful", loud volumes are - and they remain harmful (they compound the effect). – Sklivvz Mar 17 '12 at 21:57
  • Downvoted because I don't think presbycusis relates to the question. The question is being unable to hear ranges as we get older, starting from childhood, while presbycusis is specific to post middle-aged people. – Sonny Ordell Mar 18 '12 at 15:29
  • @SonnyOrdell if you look at the table, you will see that hearing loss is assumed from age 20. – Sklivvz Mar 18 '12 at 23:57
  • From what I understand that is not the same as presbycusis. Even the ISO report you link doesn't refer to the issue as presbycusis. 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. It seems the wiki page is the only source referring to range of audible frequencies in young people as presbycusis? – Sonny Ordell Mar 19 '12 at 1:47
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Although age-related hearing loss is not the norm, it's a quite common condition:

Results showed that the prevalence of central presbyacusis increased with age and that the highest prevalence was a striking 95 percent in the 80+ year age group.

The rest of my answer is based on this book, some parts of which exist online (which I'll quote). I'll be referring to this part of the website specifically.

Sklivvz already answered your first two questions, but here is a graph to illustrate it as well:

Consequently, patients with age-related hearing loss often have normal sensitivity at low frequencies, but progressively poorer sensitivity for higher frequencies, as shown here: audiogram of presbyacusis-

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.

3. Does that mean high frequency sound become less harmful as we become older and older?

It actually does! But that's because the harm has already been done...

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. 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. 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. 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.

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. Human speech is at this range, so we're particularly sensitive to it:

decibel-frequency connection in auditory perception

Does this explain that when I was younger, I was more sensitive to sound and slept less well?

Probably not, except if it was mosquitoes that were keeping you up.

Does this fact indicate some trend of our change of music taste over the time?

I don't see that it does.

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