Introduction

Noise is any unwanted or undesired sound. Noise is considered unpleasant and disrupts our hearing. However, the difference between sound and noise differs from person to person. What is noise to one person may not be noise to another. The definition of noise also depends upon the circumstances a person is in. 

The definition of noise pollution is prolonged exposure to noise. Being exposed to noise regularly causes adverse health effects in humans and wildlife, both on land and sea. WHO states that constant exposure to sound levels greater than 85 dB is hazardous to health. Constantly exposed to noise levels around 85 dB are those people working for eight or more hours near a road with high traffic or a highway. 

Noise pollution causes hearing loss, high blood pressure, and stress. In the oceans, noise from ships and trawlers is harmful to species like dolphins and whales. These sea animals depend on echolocation (obtaining the location of objects through reflected sound) to move around in the ocean. Thus, the noise from human sea activities causes great harm to marine animals.

Amplitude, Frequency, Wavelength, and Sound Pressure Level

Sound travels as ‘sound waves. When an object vibrates, it produces sound waves. The object’s vibration causes the air molecules surrounding it to vibrate too. These vibrations are what form sound waves. 

The amplitude of a sound wave is the height of the wave measured from a mean position. The amplitude of a sound wave is directly proportional to the loudness of sound. The larger the amplitude of a sound wave, the louder the sound is; smaller the amplitude, quieter the sound. 

Frequency is the number of sound waves generated in one second. Its unit is Hz (hertz). Humans can hear frequencies anywhere between 20 and 20,000 Hz. The higher the sound frequency, the more high-pitched it is to our ears. 

The wavelength of a sound wave is the distance between two identical parts of the same wave. We usually calculate wavelength as the distance between one peak and the immediate next peak of a wave. 

Sound Pressure Level (SPL) is the pressure in a medium exerted by the sound waves traveling through it. ‘Hearing threshold’ is the lowest sound pressure that a human can hear. The highest sound pressure that a human can tolerate is called the ‘pain threshold.’  

Average Decibel Levels

Noise affects every human differently. At particular frequencies, some people’s hearing is more sensitive than others. However, prolonged exposure to very high noise levels can damage anyone’s hearing. 

The loudness of noise is measured in decibels (dB). The amount of time we can hear a sound before it damages our hearing decreases as its loudness level increases. 

Let’s start with understanding the decibel levels of the least loud activities. We will then work our way towards activities that generate the loudest sounds.

Leaves rustling in the wind, soft music, and whispers have the least loudness – 30 dB.

The average noise inside your home is 40 dB.

When we usually converse with friends and family, our sound level is 60 dB.

Noises inside an office or a car traveling at 60 mph are 70 dB.

A vacuum cleaner and an average radio generate sound at 75 dB.

Air conditioners, heavy traffic, lawnmowers, and noisy restaurants have noise levels between 80 to 89 dB (Recall that prolonged exposure to sound levels above 85 dB is harmful).

Railways stations and conversations that involve shouting are at 90-95 dB.

A motorbike generates noise at a level of 96-100 dB.

Music at weddings, dances and other events are at 101-105 dB.

A chainsaw has a noise level between 106-115 dB.

The crowd at a sports match or rock concert generates a 120-129 dB noise level.

A gunshot or an emergency siren produces noise at 140 dB. 

Noise Dose Level

The percentage of exposure time of a person to harmful noise levels is known as ‘Noise Dose.’ 100% represents complete exposure, while 0% represents no exposure. We calculate noise dose levels by dividing the total exposure time of a person to such noise by the permissible time of exposure. The higher the noise level gets, the shorter the allowed time for exposure. 

Environmental and Protection organizations usually normalize noise dose levels according to an 8-hour working day. The highest level of noise a person can tolerate is 85 dB. A person’s noise dose is 100% if exposed to a noise level of 85 dB during an 8-hour working period. 

There are many warning signs that a particular sound might damage your ears. The signs include:

1. Having difficulty in hearing yourself or others talking over the sound.
2. Your ears ring after listening to the sound.
3. Your ears hurt when listening to the sound.
4. You can hear a sort of muffled sound after leaving an area with a lot of noise. 

Sound Quality Analysis

The analysis of sound quality involves using methods to quantify sound quality. Companies or laboratories study sound quality primarily to improve products whose performance is based on their sound. Examples include audio equipment such as speakers, mobile phones, air conditioners, vehicles, etc. Sound quality measures the effect of sound from different sources on the human ear. Sound quality is influenced by how we perceive sound. Psychoacoustic parameters are taken into account when analyzing sound quality. The four main psychoacoustic parameters are:

1. Loudness
2. Sharpness
3. Roughness
4. Fluctuation

To measure sound quality, apply the above metric parameters to the sound signal detected. However, issues related to noise pollution cannot be overcome solely by these parameters, and there are many other factors that we must take into account.