Why do we only hear between 20Hz and 20khz

[mkj]

i no that the frequency range limits are determined by the cochlea where the low frequency sounds are localized on one terminal and the high frequency on the second end, but i am wondering if there exist a formula that permits to calculate these ranges analytically

 

[CWatters]

Although your brain cannot hear frequencies below about 20 Hz there is evidence that the structures of the ear respond to much lower frequencies - for example when driving up/down a hill we can detect exceptionally low frequency pressure changes caused by changes in altitude.

Some fields of science use very low frequencies to bias structures in the ear...

http://oto2.wustl.edu/cochlea/windmill.html

The research performed in our laboratory covers a number of areas related to inner ear function and the physiology of the cochlear fluids (apparent from the rest of the Cochlear Fluids website). Our group has for years been using infrasonic tones to study how the ear works. These are often described as “biasing tones”, because they allow the structures of the ear to be displaced slowly while measurements are made. For almost 10 years we have been using infrasonic 5 Hz bias tones at levels as low as 85 dB SPL (shown as the green diamond in the graph at the right) to manipulate cochlear responses in guinea pigs. The guinea pig is LESS sensitive to low frequencies than the human, so this makes you realize that low frequency infrasonic sounds ARE AFFECTING THE FUNCTION OF THE EAR at levels well below those that are heard by humans.

 

[sophiecentaur]

One reason for the lower limit to hearing must surely be that it gets progressively harder to 'match' the impedance of a small diaphragm like the eardrum to the impedance inherent in the hairs of the cochlea.
Another reason could be simply that evolution has made our hearing range 'just good enough' to function adequately as an organism - as with pretty much every one of our senses and abilities. Cost-benefit analysis rules.

We all know that Elephants have big ears - but that's because Noddy won't pay the ransom. Boom boom.