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LESSON NOTES

Range of Frequency

Inaudible sound

Human ear cannot detect sound frequencies less than 20 vibrations per second i.e.

20 Hz. So any sound below this frequency will be inaudible sound for humans. In the
high-frequency range, the human ear cannot detect frequencies above 20000

vibrations per second (20 KHz) and the amplitude of the wave would be depending
on the loudness of the sound. So the frequencies below 20 Hz and above 20 KHz

comes under the category of inaudible frequencies. The low-frequency sound which

human ear cannot detect are also known as infrasonic sound. Whereas the higher
range inaudible frequency are also known as ultrasonic sound.

Some animals like dogs have the ability to hear sounds having frequencies higher
than 20 KHz. The police department uses whistles with frequencies higher than 20

KHz so that only dogs can listen to it. Inaudible frequencies are helpful for many

purposes. These are used in many fields like research and medical. The ultrasound
equipment used for tracking and studying many medical problems works at

frequencies above 20 KHz.

Audible sound

The human ear can easily detect frequencies between 20 Hz and 20 KHz.
Hence sound waves with frequency ranging from 20 Hz to 20 KHz is known are

audible sound. The human ear is sensitive to every minute pressure difference in the
air if they are in the audible frequency range. It can detect pressure difference of less

than one billionth of atmospheric pressure.

As we grow older and are exposed to sound for longer period of time, our ears get
damaged and the upper limit of audible frequencies decreases. For a normal middle-

aged adult person, the highest frequency which they can hear clearly is 12-14
kilohertz.