The
sounds produced in our environment can be of different frequencies. Humans
cannot hear sounds of all frequencies. For example, if the frequency of the sound
is less than 20 Hz (the unit of measurement of frequency), humans cannot hear
it, and if the frequency of the sound is more than 20,000 Hz, it is also not
audible to humans. This means that the human ear cannot hear frequencies below
20 Hz and above 20 thousand Hz. The human ear can hear frequencies of 20 to 20
thousand hertz. The frequency range of 20 to 20 thousand hertz is called an
audible range of sound.
So we can also say that "the range of sound
frequencies that can be heard by the human ear is 20 to 20 thousand hertz."
sounds
with a frequency of less than 20 Hz are called infrasonic sounds
or infrasonic. As such, infrasonic is very low-frequency sounds.
Infrasonic sounds cannot be heard by the human ear. Infrasonic sounds are
produced by bodies that vibrate very slowly. For example, a vibrating simple
pendulum produces an infrasonic sound. We
cannot hear the sound
of this simple vibrating pendulum because it vibrates with a frequency of less
than 20 Hz. Earthquakes and some animals such as whales, elephants, and rhinos
also produce infrasonic sounds. Rhinos produce infrasonic sounds with a frequency
of less than 5 Hz to communicate with each other. It has also been observed
that some animals get scared and start running before an earthquake. This is
because earthquakes before large shock waves produce low-frequency infrasonic sounds
that some animals can hear and become uncomfortable.
Sounds
with a frequency of more than 20 thousand hertz are called ultrasonic sounds.
Similarly, ultrasonic sounds
are very high-frequency sounds. Ultrasonic sounds
cannot be heard by the human ear. Although humans cannot hear ultrasonic
sounds, dogs can hear these sounds up to 50,000 frequencies. For this reason,
dogs are used by the police in detective work. Leopards, bears, deer, cats,
dolphins, snakes, and cheetahs can hear ultrasonic sounds.
Bats can hear frequencies up to 120,000 hertz. Bats can also produce ultrasonic
sounds of up to 20,000 hertz when chirping.
We
cannot hear the cries of bats because their cries are ultrasonic sounds with a
frequency of more than 20 thousand hertz that cannot be heard by the human ear.
Bats, dolphins, and rats can produce and hear ultrasonic sounds.
Children under the age of 5 can hear ultrasonic sounds up to a frequency of
25,000 Hz. With age, the human ear's ability to hear high-frequency sounds
decreases. The ultrasonic sound
cannot be produced by conventional vibrating bodies such as a tuning fork. They
can be produced with the help of special vibrating bodies that vibrate very
fast.
