What is Sound? What is Noise and Noise Pollution?

What is Sound?

Sound is a form of energy, just like electricity, heat or light. When you strike a bell, it makes a loud ringing noise. Now instead of just listening to the bell, put your finger on the bell after you have struck it. Can you feel it shaking? This movement or shaking, i.e. the to and fro motion of the body is termed as Vibration. The sound moves through a medium by alternately contracting and expanding parts of the medium it is travelling through. This compression and expansion creates a minute pressure difference that we perceive as sound.

What is Noise?

The definition of Noise is a hazy one. The boundaries are blurry. Our perception of objects, in case of both visual and auditory, is subjective as in it depends from person to person. A rock and roll fan will love the loud music but the case isn’t so with one who prefers classical music. To that person, rock will seem like noise. Due to this noise’s definition is restricted to ‘Noise is a variety of sound which is unwanted, mainly because it cannot be heard clearly due to mixing of sounds or due to the loud and jarring nature of the sound.’ You cannot increase or decrease noise. It just enters the system as you make sounds. Even when you are talking to your friend in the room there is noise. In you classroom, if you talk while your teacher is teaching, you’re creating noise in the system. If the phone rings when you’re in your room studying, it is defined as noise.

Noise also has another definition in digital recording systems. An ideal equipment for recording would record the sound perfectly. Since in the real world, we have to deal with real equipment, not ideal, some impurities are introduced into the system. These impurities being unwanted fit the definition of Noise pollution. This is also the static you hear when you are tuning your radio station. The static you hear is termed as White Noise.

Measurement of Sound: Decibel Meter and its unit, Decibel.

For us to demarcate what is noise and what is not, we need to be able to measure the sound waves. The instruments that are used to measure the sound intensity levels are known as Decibel Meter. A decibel meter calculates the intensity of the sound travelling through air from its source by measuring the pressure of the sound waves.


We know that sound waves travel by the means of minute changes in pressure due to compression and expansion of the molecules of the medium. This is why decibel meters are also referred to as Sound Pressure Level meters. This device gives its reading through the help of a scale whose units are Decibel. This scale was pioneered by the inventor of the telephone, Alexander Graham Bell. The decibel scale operates on a logarithmic scale due to which an increase of 10 dB is perceived twice as loud by our auditory system. Similarly, an increase of 20 dB is perceived as four times as loud. So 60dB is twice as loud as 50dB and 70dB is four times as loud as 50dB.

Noise Pollution

Noise is one of the most common occupational health hazards. In heavy industrial and manufacturing environments, machinery is a constant source of unwanted noise and with the advent of mass production, this problem has been aggravated. Rows and rows of production units lead to a lot of noise around the workers. Prolonged exposure to such loud noises can cause permanent damage to the human auditory system.

To prevent adverse outcomes of noise exposure, noise levels should be reduced to acceptable levels. The best method of noise reduction is cut it out at the source. Generators and machine nowadays are padded in a shell to reduce the noise they create. Where this technology is not applicable, adequate external protection should be used such as ear muffs or plugs.

This article explains in details sound, noise, measurement of sound namely decibel and decibel meter, the effects of noise pollution and finally the means to prevent noise pollution. To know more regarding the sound and its various characteristics, please visit BYJU’S.com. Join us and fall in love with learning.

Practise This Question

 What are the sources of noise pollution in our surroundings?