An average young person can hear a staggering range of sound vibrations from 20 Hz to 20,000 Hz. (A Hertz is one vibration per second. So 20,000 Hz is a vibration that happens 20,000 times each second.) Of course, you won’t hear all pitches equally well. The middle-range pitches are the easiest to detect. A sound that’s similarly loud but extremely high-pitched will seem much quieter to your ear. You’ll notice a similar fall-off as you descend to the rumbles of low-frequency sound, although you’ll begin to feel them reverberate through your body.
As you age, the upper range of your hearing shrinks. For example, the hearing of a normal, middle-aged adult tops out at a significantly lower (but still impressive) 14,000 Hz. This change has been used to some effect by clever people on both sides of the age divide. For example, one company sells a sound device called the Mosquito Ultrasonic Teen Repellent (www.noloitering.ca). It emits an annoying sound that only young people can hear. Put it in a place where you don’t want crowds of teenagers to loiter—say, a mall parking lot—and it’s sure to drive them away. A similarly inventive product is the Teen Buzz ringtone (www.teenbuzz.org). Teenagers use it to announce text messages on their cell phones without alerting teachers and other authority figures in the over-30 crowd.
To test your own hearing and find the highest frequency you can detect, try an online hearing test (like the one on www.phys.unsw.edu.au/jw/hearing.html). Of course, these tests depend on some factors you can’t control, such as the quality of your speakers and the noise your computer makes, so they’re not perfectly accurate.
Source of Information : Oreilly - Your Body Missing Manual