Ethan Siegel in Starts With A Bang:
A couple of weeks ago, my wife and I went to the circus together. Someday, I vowed, I'll be strong, flexible, and stable enough to do the amazing hand-balancing tricks we saw. And all the while, the six-year-old girl behind us screamed her piercing, high-pitched scream, cheering the performers on. (This is totally appropriate behavior, IMO, and no children reading this should be discouraged from screaming at the circus.)
Now, one of us has better hearing than the other. And while one of us found the high pitched screaming to be a minor annoyance, the other was simply in agony. What's going on here?
It's going to take a little bit of biology and a little bit of physics to figure it out. First off: how does your ear work?
The sound waves — which are pressure waves — enter your ear and press up against the tympanic membrane, better known as your eardrum.
The vibrating eardrum causes the three little bones in there — the hammer, anvil, and stirrup, known collectively as the auditory bones — to vibrate as well. The last one, the stirrup, pushes against the cochlea, and this is where your hearing takes place. How? To get the simple answer, we need to know what the cochlea looks like on the inside?
Your cochlea is a spiral-shaped structure, like a snail's shell, that's filled with fluid and lined with tiny hairs known as cilia. The most sensitive cilia are the ones closest to the outside: only a tiny vibration is needed to set them in motion. These are also the most easily destroyed. So when you do things to damage your hearing like go to rock concerts without earplugs, listen to your headphones or stereos too loudly, fire a gun without protective gear, or have your “friend” scream in your ear, these sensitive cilia get destroyed.
The bad news? Once they're destroyed, they pretty much never grow back. So while a newborn baby can hear up to about 20,000 Hz, very few adults can. At age 31, my hearing stops somewhere around 13,000 Hz. There are a few sites out there to test your hearing, so I've stolen some sound files to allow you to find where your hearing, approximately, cuts out.
More here. [I could hear the 12KHz tone clearly, the 14K just barely, and the 15K not at all.]