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Properties of Sound
All sounds that we hear are not the same. There are some properties that differentiate one kind of sound from another. We will study about these properties now.
It is defined as the characteristic of a sound that enables us to distinguish a weak or feeble sound from a loud sound. The loudness of a sound depends on its amplitude. Higher the amplitude louder will be the sound and vice-versa. When a drum is softly beaten, a weak sound is produced. However, when it is beaten strongly, a loud sound is produced. The unit of loudness of sound is decibel (dB) .
More to know
Amplitude is the maximum displacement of a vibrating particle from its mean position. It is denoted by ‘A’. The unit of amplitude is ‘metre’ (m).
The pitch is the characteristic of sound that enables us to distinguish between a flat sound and a shrill sound. Higher the frequency of sound, higher will be the pitch. High pitch adds shrillness to a sound. The sound produced by a whistle, a bell, a flute and a violin are high pitch sounds.
Normally, the voice of a female has a higher pitch than a male. That is why a female’s voice is shriller than a male’s voice. Some examples of low pitch sound are the roar of a lion and the beating of a drum.
Quality or Timbre
The quality or timbre is the characteristic of sound that enables us to distinguish between two sounds that have the same pitch and amplitude. For example in an orchestra, the sounds produced by some musical instruments may have the same pitch and loudness. Yet, you can distinctly identify the sound produced by each instrument.
Audibility and Range
According to the frequency we can classify the sounds into three types. They are:
* Audible sound
* Infrasonic sound
* Ultrasonic sound
Sound with frequency, ranging from 20 Hz to 20000 Hz is called sonic sound or audible sound. Sound with this frequency range alone can be heard by the human beings. Human ears cannot hear sounds with frequencies below 20 Hz or above 20000 Hz. So, the above range is called as audible range of sound.
A sound with a frequency, below 20 Hz is called as subsonic or infrasonic sound. Humans cannot hear the sound of this frequency, but some animals like dog, dolphin, etc. can hear. Uses of infrasonic sound are:
* It is employed in the earth monitoring system.
* It is also used in the study of the mechanism of human heart.
A sound with a frequency greater than 20000 Hz is called as ultrasonic sound. Animals such as bats, dogs, dolphins, etc. , are able to hear certain ultrasonic sounds as well. Some of the uses of ultrasonic sounds are:
* It is extensively used in medical applications like ‘sonogram’.
* It is used in the SONAR system to detect the depth of the sea and to detect enemy submarines.
* It is also employed in dish washers.
* Another important application of ultra sound is the Galton’s whistle. This whistle is inaudible to the human ear, but it can be heard by the dogs. It is used to train the dogs for investigation.
A bat can hear the sounds of frequencies higher than 20,000 Hz. Bats produce ultrasonic sound during screaming. These ultrasonic waves help them to locate their way and the prey.
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