How human hearing works [Basic]

DISCLAIMER: I only do this as a hobby because I have some interesting hearing loss.  All the information below could be wrong.  I take no responsibility for whatever is done with it.

Notes:
• You have 3 rows of OHC's (Outer Hair Cells) in each ear - about 12K per ear.  They along with 3.5K IHC's (Inner Hair Cells) per ear ride on the basilar membrane.
 • Both types of cells have to last your whole life.  They don't divide or really repair themselves.

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The huge attenuation at the high end can also depend on how well your Outer/Inner Hair Cells are functioning, shape of your ear canal, shape of your eardrum, compliance of your eardrum, pressure in your middle ear, perilymph/endolymph fluid levels, ion concentration, flexibility of the oval and round window, etc.
  • For me, I can insert silicone ones w/a solid filter and still hear me lightly rub my fingers together from half-arms length (12-15khz).

Anyway, when a pressure (sound) wave comes in it moves your tympanic membrane (eardrum) and transfers the motion to the 3 small bones in your ear, the bones in turn push/pull on the oval window (a membrane) on the outside of your cochlea.  The movement causes waves in the fluid your basilar membrane is surrounded in (causing it to ride the wave).

OHC rows 1-3 then pick up on the movement and move themselves to amplify the frequency they're tuned for (on a healthy ear this can be 50-60dB and happens in nanoseconds), with that amplification the Inner Hair Cells now have enough movement to send a signal to your brain.
  • Hearing aids "replace" the outer hair cells (they usually get damaged first).

A few hundred milliseconds after the sound your natural hearing protection (tensor tympani muscle) and some stabilization (from the stapedius muscle) kicks in.  The attenuation and stabilization varies from person to person, age groups and how used to loud sounds you are, etc.
  •The tensor tympani is attached to the malleus bone (very close to the eardrum) and the other muscle is attached to the stapes (farthest away from the eardrum).

Without the OHC's (if I remember correctly) you need around 70dB for IHC's to start to do their job.  I.e. to actually send the electrical signals to your brain (they're very robust, but not very sensitive).

There's also calcium, potassium and sodium ions that are used to depolarize and partly feed the OHC's.  And when you're exposed to loud noise (even if it doesn't exceed the mechanical tolerance of your cochlea) you end up messing up the balance of all those ions (Ca2+ mostly AFAIK).

IMO it's all overly complicated, way too small and very prone to damage.  And we're not even taking into account blood flow, blood glucose, auditory nerve amplification, your brain and how you personally learned to hear.

Anyway, if you're listening to music at a locked level you can EQ Yourself with a custom Equal-loudness contour (Fletcher Munson Curve).  Every frequency should sound like it has equal loudness to you.
 • This is what Auddssey Dynamic EQ does.  It lets you listen to your track while keeping the balance between frequencies regardless of the volume level.

And if you flatten your cans you can look up the offsets to convert from dB SPL to dB HL and do your own hearing test.  Or hearingtest.online has a pretty accurate one if you have flat cans and match the volume to a real hearing test you had the same day.

I hope someone finds this info interesting. :)