Elements of Sound Quality
Timbre: The quality of sound is called the timbre of sound. Timbre is one of the characteristics of sound that enables us to differentiate between two different types of sound, just like we can hear that sound of guitar and harmonium or other musical instruments are all different.
Different persons produce the sound of the different timbre. Because of different timbre in sound, the voice of different persons can be recognized.
Tone and Note of sound:
The sound of a single frequency is called tone and sound of the mixture of several frequencies is called note. A note is pleasant to listen.
Noise is unpleasant to hear.
Music is pleasant to hear because of good quality, i.e. timbre while noise is unpleasant because of bad quality.
Medium is a must for propagation of sound wave
A soundwave travels by the compression and rarefaction of the particles, so a medium is necessary for the propagation of the sound wave. Sound cannot propagate without a medium. Thus Soundwave cannot propagate through vacuum. This can be demonstrated using the bell jar apparatus.
When all air is vacuumed out of bell jar, the sound of the bell is not heard outside. This happens because there is no medium present, consequently no particles present for compression and rarefaction in the bell jar through which sound waves could propagate.
Propagation of sound and media in which it travels:
Sound propagates through solid, liquid and gas. In all these media; sound wave propagates by the compression and rarefaction of particles of the medium.
Velocity of sound wave in different media:
The velocity of sound waves depends upon the following three factors:
- Nature of the medium
- Humidity present in the air
How medium influences velocity of sound:
The velocity of sound is maximum in solid, moderate in liquid and minimum in gas.
The velocity of sound is directly proportioned to temperature. This means the velocity of sound increases with increase in temperature. For example, sound wave at 0C in the air is 332m/s. The velocity of sound waves at 20C in the air is 344m/s. This is the reason, we hear more clearly on a hot day than on a cold day.
Since the velocity of soundwave in water is more than that in the air, so the humidity in the air increases the velocity of sound. Therefore, an increase in humidity in the air increases the velocity of sound and a decrease in humidity in air decreases the velocity of sound. This is the cause that we can hear more clearly in the rainy season than in summer.
Audible Range of sound
The human ear can hear the sound between frequencies of 20 Hz to 20,000 Hz. Thus, audible range or range of hearing is between 20 Hz to 20,000 Hz; for human beings. However, children under 5 years of age can hear the sound up to 25000 Hz.
Sound beyond audible range of human being is called Infrasound and Ultrasound
Infrasonic Sound or Infrasound
Sound, below the frequency of 20Hz, is called infrasonic or infrasound. Infrasound is produced because of very slow vibration. For example; simple pendulum produces sound below 20Hz. A human being cannot hear infrasound as their ears are not adapted to hear the sound of such range.
Many animals; such as whale, elephant, rhinoceros, etc. can produce and hear sound having frequencies below 20 Hz.
Ultrasound or Ultrasonic Sound
Ultrasound or ultrasonic sound:- Sound, above the frequency of 20000 Hz is called ultrasound. Humans cannot hear the ultrasonic sound. However, many animals such as dogs, cat, bat, monkey, deer, etc. can hear ultrasound.
Bats catch their prey by producing ultrasound. Bat produces ultrasound and detects the reflected sound waves coming from any obstacle; such as a prey. By detecting the reflection of ultrasound, bat understands the position and type of prey or of any obstacle in the way. Some aquatic animals, such as dolphin, also use ultrasound to catch their prey.
USE OF ULTRASOUND
Ultrasound is sound waves of high frequency. Because of high frequency, ultrasound is associated with more energy and can penetrate up to a large extent. This characteristic of ultrasound makes it very useful for many purposes. Some of its uses are given here:
In the detection of ailments in the human body.
In the cleaning of machinery parts which are beyond reach without disassembling of parts.
Detection of any deformities in metal blocks.
Detection of any blockade in pipe lines.
SONAR: The full form of SONAR is Sound Navigation And Ranging. This is a device which is used to measure the depth of seabed, locate scraps, wrecks, submarines of enemies, etc. in the water by producing ultrasound. It is fitted over ships and submarines.
Ultrasonic sound waves are produced by SONAR and when these waves return after reflection from anything in the water, they are analyzed with the help of a computer. The shape and position of objects undersea and ocean are detected on the basis of speed and nature of reflected ultrasound waves.