I've recently seen the following image:

enter image description here

Source: https://commons.wikimedia.org/wiki/File:Hoerflaeche.svg

Translation (from German):

  • The upper boundary (Schmerzgrenze) is where it starts to hurt
  • "Musikwahrnehmbarkeit" is where you can hear music
  • "Sprachwahrnehmbarkeit" is where you can recognize speech
  • "Hörschwelle" is absolute threshold of hearing (ATH)

While the ATH seems to be relatively smooth, there is a noticeable "gap" between 2kHz and 5kHz. Does anybody know why this is the case?

Some possible explanations I've heard are:

  • Evolution: Hearing a baby cry
  • Evolution: Hearing leafs rustling
  • Coincidence: There is no good reason for that.

The image is from wikipedia commons and has no references. It might be wrong. Do you know similar graphs? Do you eventually have this kind of information for other animals?

  • $\begingroup$ English is not my mother tongue. If you spot any errors / sentences which you would formulate differently, please do so. I learn by looking at those mistakes and I'm happy even if you only correct minor mistakes. $\endgroup$ – Martin Thoma Dec 20 '14 at 11:52
  • $\begingroup$ I would really like a more thorough answer to this. $\endgroup$ – Arturo don Juan Nov 3 '16 at 3:58

Acoustically, we hear better in the 2-5 kHz range because our auditory canal resonates in that range (specifically, around 3 kHz). Our ear looks something like this (U Miami):


The auditory canal is part of the outer ear, which amplifies sound so that it can be converted into electrochemical signals by the middle and inner ear. We hear better in the 2-5 kHz range because the resonant frequency of the auditory canal is in that range.

The mechanical question of "how does this work" is usually easier to answer than the "why did this evolve?" question. Since reproductive fitness is the driving force of evolution, hearing babies crying (between 1-5 kHz) is the best guess I can come up with.

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  • $\begingroup$ Do you think the resonant frequency could be different without severely influencing other properties how we hear / what we hear? Is this different for other animals with similar ears? $\endgroup$ – Martin Thoma Dec 21 '14 at 21:26
  • 1
    $\begingroup$ Changing the resonant frequency wouldn't change what we hear but would change the threshold at which we hear different things. I don't actually know about other animals, perhaps ask another question if you want more information? $\endgroup$ – Luigi Dec 21 '14 at 21:29

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