Introduction To Sources of Noise

Cities today have become the epicenters of noise pollution. Drivers honking horns, road workers drilling roads, aircrafts flying overhead, all of these are sources of noise pollution. Although it is invisible, noise can cause severe damage to humans. Noise pollution also causes significant damage to wildlife. It affects the breeding cycles of wild species. Some experts say that noise pollution is causing accelerated extinction rates of some species.

There are many sources of noise pollution. However, the main sources of noise pollution are:

1. Road traffic: The honking of a bus produces noise at 100 dB, and a car produces 90 dB. A motorbike generates a noise level of 95 dB.

2. Air traffic: One single aircraft produces noise between 100-200 dB. Imagine the noise from tens of airplanes flying over cities every day.

3. Construction sites: The drills used in the construction or maintenance of roads and pavements generate noise of 110 dB.

4. Nightlife and events: Open or rooftop bars and restaurants produce more than 100 dB of noise. Apart from bars, events such as weddings and dances also produce noise at a similar level. Rock concerts create noise at around 120 dB.

5. Animals such as cats and dogs: When barking or howling, dogs generate a noise level between 60 to 80 dB.

Measurements of Noise

The standard used for measuring noise is the decibel (dB). Decibels indicate how much air vibrations make up a sound. The lowest sound that humans can hear on a decibel scale is 0 dB. The level at which sound becomes painful to hear is 80 dB.

A Sound Level Meter (SLM) is the most commonly used instrument to measure noise.

The basic structure of an SLM consists of a display screen, electronic circuits, and a microphone. The microphone detects the vibrations in the air produced from a sound. The circuits convert the detection of air pressure into electrical signals. These signals then travel to the display screen, where the expression of noise level is in decibels.

To detect the noise level in an area, one should be holding the SLM at arm’s length. It should be leveled to the ear and pointed at the noise source. It can only measure the noise level in an area at that instant and does not give a continuous reading of the variation of noise levels from a sound source. Therefore, it is not an ideal measurement form if someone wants to determine their exposure to noise over a day.

Characteristics of Noise

There are two essential characteristics of sound or noise. They are:

1. Amplitude
2. Frequency

The expression of these two characteristics is essential to determine and evaluate the noise level.

The definition of frequency of sound is the number of cycles in a sound wave generated per second. It is expressed with the unit Hertz (Hz). Noise that is below 250 Hz is called low-frequency noise. Noise that is higher than 2000 Hz is called high-frequency noise. Noise falling between 250-2000 Hz is called mid-frequency noise.

The amplitude of the sound is the measurement of the height of a sound wave from a median position. Unit of Amplitude is decibels (dB) . The decibel scale is logarithmic. Small increments in decibel levels on a logarithmic scale correspond to huge increments in sound energy.

Effects of Noise Pollution

Constant exposure to loud noise can damage human health in several ways. Noise pollution impacts millions of people every day, and some do not even realize it. Children and the elderly are the populations most affected by noise pollution. A study on children living near busy streets and airports found that they suffer from stress. Apart from stress, they also suffer from memory impairments, poor reading skills, and decreased attention levels.

Excess levels of noise even affect animals. Studies have found that a caterpillar’s dorsal vessels (their heart) beat faster when exposed to loud noises. Noise pollution even causes hatchling failure in birds. Animals such as bats use their sound to navigate, attract mates, escape predators, and find food. Noise pollution interferes with their ability to perform these tasks, decreasing their chance of survival.

Apart from land animals, noise pollution even affects animals in the ocean. Dolphins and whales depend on the reflection of sounds to find food, navigate, and find mates. Noise pollution caused by ships, oil rigs, sonar submarines, and underwater seismic studies does not allow them to perform their basic tasks effectively. Noise pollution in the ocean also damages the ears of marine animals, causing grave injuries. Whales get stranded on beaches and die due to noise interference with their ability to echolocate.

Auditory Effects

Noise-induced hearing loss is the single most common effect of noise pollution on humans. Single exposure to high-intensity sound or long-term exposure to sound levels higher than 85 dB can induce hearing loss. Exposure to such sounds damages the cochlea, a part of the inner ear responsible for hearing. Large sounds damage the hair cells in the cochlea. These cells cannot regenerate. Therefore, We can preserve our hearing ability only by preventing exposure to noise.

Non-Auditory Effects

Apart from hearing, noise pollution can damage human health in several ways. Some of the main non-auditory effects of noise pollution are:

1. Psychological effects: Noise can cause anxiety, depression, fatigue, and stress in humans and animals.

2. Sleep disorders: It is almost impossible to sleep when the surrounding noise exceeds 45 dB. Lack of sleep can further affect our behavior, making us aggressive and irritable.

3. Memory: A high level of noise is harmful to memory. It reduces our ability to focus and makes it difficult to study in the case of children.

4. Physical effects: Noise pollution causes people to develop high blood pressure and headaches. When exposed to loud sources of noise pollution making a loud noise for a long period, can cause a heart attack.

Standards and Application

Below are the noise standards as prescribed by WHO for various indoor and outdoor activities.

1. Inside homes – 30 to 35 dB
2. Inside school classrooms – 35 dB
3. Outdoor playgrounds – 55 dB
4. Inside hospitals – 30 dB
5. Around industrial and commercial areas – 70 dB
6. Festivals, ceremonies, entertainment events – 100 dB
7. Listening to music through headphones – 85 dB

Applications include designing and installing equipment to solve problems that stem from noise pollution. They involve designing school classrooms, places of worship, theatres, office buildings, etc., in a way that does not allow outside sound to leak in. The design, along with the installation of sound equipment, enhances indoor acoustics.

Also Read: Effects of Noise Pollution on Plants and Animals