Sound is air getting pushed and pulled really fast. It bumps your eardrum, three tiny bones pass the bump along and make it stronger, and it reaches a curly tube called the cochlea. The clever part: the curl works like a piano (high notes ring one end, low notes ring the other) and tiny hairs there tell your brain. Slide the pitch in the simulator and watch a different spot light up.
Most people think hearing fades evenly across all pitches as you age. In fact it wears out from the top down, because the high-frequency hair cells crowd near the cochlea's entrance where every sound passes first and takes the most punishment.
What's actually happening
It helps to remember that sound is not a thing that travels so much as a pattern that travels. A guitar string shoves the air next to it, that air shoves the next layer, and a wave of squeeze-and-stretch races outward at about 343 metres a second. Nothing is actually delivered to your ear except this rhythmic pressure. Everything else (the music, the warning, the voice you love) is built inside your head from that one humble input.
The ear is a chain of clever translators. The pressure wave funnels down the canal and drums on the eardrum, a membrane thinner than paper. Behind it sit the three smallest bones in your body (the hammer, anvil, and stirrup) which lever the motion and, crucially, concentrate it onto a tiny window, boosting the force enough to push against liquid. Beyond that window is the cochlea, a fluid-filled tube coiled like a snail shell. And here is the masterstroke: the cochlea is tuned along its length. It is stiff at the entrance and floppy at the far tip, so a high note makes the entrance shiver while a low note travels all the way in to ring the tip. Pitch becomes a place. Thousands of hair cells sit along that strip, and whichever ones get shaken fire a nerve, so your brain reads "which spot" as "which note".
The strange consequence is that hearing wears out from the top down, and unevenly. The high-frequency hair cells crowd near the entrance, where every sound passes first, and they take the most punishment, so the very top of your range fades a little every year — most adults have already lost the highest notes a child can hear, which is why some shops play a thin 17 kHz tone teenagers find unbearable and grown-ups cannot detect at all. Loud noise kills these cells outright, and they never grow back. The ringing after a concert is them screaming; the silence later is some of them gone for good.
Pitch becomes a place: the cochlea sorts each frequency to its own spot, which is why hearing loss is so often loss of specific notes.
- 1Hum a very low note with your hand flat on your chest, then a high note. Feel the low one buzz lower and broader, the high one tighter and higher up.
- 2Now find a free "hearing test" tone sweep and play it quietly from low to high, noting where it gets thin or vanishes for you.
- 3That cut-off is the top of your own cochlea. Compare it across people of different ages and watch the ceiling drop with the years.
Common questions
The high-frequency hair cells sit near the cochlea's entrance, where every sound passes first, so they take the most punishment and the top of your range fades a little each year. Loud noise kills them outright, and they never grow back.
It is tuned along its length, stiff at the entrance and floppy at the tip, so high notes shiver the entrance and low notes travel all the way in. Pitch becomes a place, and whichever hair cells shake tell the brain which note it is.
The stapes, or stirrup, in the middle ear is about 3 mm long, the tiniest bone in the body. It is one of three bones that lever the eardrum's motion onto the cochlea's fluid.