Month August 2017

            There are many ways in which sound pollution affects a human being. It can cause hearing problems, sleep disorders, cardiovascular issues, and other health issues. Let us look at a few of them in detail.

            As you may know, unwanted sounds that our ears are not able to filter, may cause serious problems to the body. Certain sounds when exceed the limit, disturb our ears. For example, the sound of aeroplanes or horns.

            Constant exposure to such sounds can damage our ear drums, and cause hearing loss. Then there are sleep issues one develops due to loud sounds. If we are not able to sleep properly, it will in turn cause fatigue.

            Many studies in the past have suggested that the occurrence of aggressive behaviour and fatigue can be linked to noise pollution. In the later years of life, these conditions can possibly lead to chronic health issues.

          Like human beings, animals too are vulnerable to loud noises. A clear example can be seen if you have a pet dog at home. When it hears noises from firecrackers, for instance, it quickly moves to places that keeps it away from the sounds. Helpless animals like these get easily scared by high intensity sounds. 

          Not just for dogs, but for birds too, noise pollution proves to be costly. Often, sounds from planes, road traffic and machinery in urban areas destroy their habitats, and change their normal ways of life. For owls and bats in particular, unwanted sounds affect prey-hunting.

          Another species that get affected by sound pollution is elephants. Environmentalists warn that helicopter rides and other noisy events around their habitats can cause the animals to flee the area out of fear. This in turn, will affect the entire ecosystem.

          In fact, noise pollution is one of the many factors that contribute to the depletion of wildlife population. 

                Almost all species on Earth are prone to the hazards caused by sound pollution. Marine animals are no exception. Many studies have shown that loud sounds often cause major problems to the health of marine lives.

               It is true that many of these animals need sound to navigate, to find food and mates, and to communicate. Yet, when the sounds become noise, they find it unbearable.

               The main threats before them are military sonars, large ships, explosives, underwater construction and air guns. The effects caused by these factors are various. They include temporary and permanent hearing loss, disruption of communication, and subsequent stranding, habitat loss, serious injuries or even deaths from hemorrhaging and tissue trauma.

              While bigger fishes like whales and dolphins show a greater resistance, smaller ones and soft shelled species like prawns, molluscs etc, are more sensitive to noise. 

            Noise calculation refers to the process of calculating the level of noise emission using the metric dB (A). Noise emission, as we know, is created by sources of various types f that emit unwanted noise into the environment.

            There are a number of different national and international standards that have been defined over time to calculate noise. The quality of the results, however, depends on the quality of the acoustic data provided, and the capability of the noise calculation engine.

            As mentioned earlier, decibel is the main unit to measure the intensity or loudness of sounds. But it can also be measured using its pitch, which is the frequency of sound vibrations per second.

            Usually, sound is recorded with a microphone. But a sound level metre uses a sound sensor. They work like microphones, but with more accuracy.

            India is one of the many countries in which noise pollution is a major problem.

            As a measure towards controlling noise pollution, the Noise Pollution Rules, 2000 was framed.

            It set rules and regulations regarding the noise levels to be maintained in certain areas. That is 75 decibels in industrial areas, 65 decibels in commercial areas, and 55 decibels in residential zones.

           Along with this came the observance of a silence zone, which does an area comprise not less than 100 metres around hospitals, educational institutions, courts, religious places etc. According to this rule, no permission can be granted by any authority for use of a public address system in the open after 10.00 p.m. and before 6.00 a.m.

           It also allows for prosecution of people who violate the rules regarding noise pollution. 

            For a long time, countries regarded unwanted, loud sounds as a ‘nuisance’ rather than as pollution. But today, many countries in the world have framed laws and rules to keep excessive noise under control.

            In the US, for example, there are federal standards for highway and aircraft noise. The Noise Pollution and Abatement Act of 1972 is the country’s statute that initiates a federal programme of regulating noise pollution.

            Another country that has strict restrictions on noise levels is Japan. The country’s ‘Anti-Pollution Basic Law’ covers sound pollution. There is a national council as well, under the chairmanship of the prime minister that controls the quality of air, water, and earth vibrations caused by construction work.

            In the UK, the Noise Abatement Act makes provision to curb unwanted noise and vibration as a measure to ensure safety.

           As we saw earlier, the idea of waves can be best understood through the example of a stone thrown into still water. This act produces rings of small waves, or ripples on the surface of water. We can see them spread out in even, concentric circles, from the point where the stone falls.

          Depending on the size of the stone, the size of the circle too varies- the larger the object, the larger the waves. In this context, the movement of waves is produced by the up-and-down motion of particles in the water. Such waves are called ‘transverse waves’. Another example is the water waves in the ocean, which move up and down.

         Sound waves, on the other hand, move in a different pattern. Their vibration is caused by the back-and-forth movement of particles. Such waves are called

          ‘Longitudinal waves’. They travel in the same direction as the vibration, or disturbance that causes them. As the waves travel through a medium, the molecules or particles collide with each other in the same direction and the waves keep moving. 

            Supersonic speed refers to a speed greater than that of sound. A bullet fired from a modern-day gun is said to have this kind of speed. Another important example is the supersonic aircraft.

            As the name suggests, they are flights that travel faster than sound. Historically, they were developed in the second half of the 20th century. It is said that US Air Force Captain Charles E. ‘Chuck’ Yeager was the first person to fly an aircraft faster than the speed of sound, in 1947.

            One of the earliest and supersonic flights that was used as a passenger aeroplane was the Concorde. Its speed was twice the speed of sound, and was said to fly between London and New York in around three and a half hours! However, the flight is no longer used.

            An Indian example of a supersonic flight is the HAL Tejas, which is still in service. 

          Imagine yourself in a sea. You see different kinds of waves there – big ones, small ones, huge ones, and sometimes, scary ones too.

          The highest point of each wave is called the crest. Suppose you are floating on a wave crest, and can see the crest of another wave in front. Then, you are looking at the wavelength of those waves. In other words, wavelength is the distance between two identical points on two back-to-back waves. In this case, it is the distance between two crests. Similarly, there are also something known as troughs, which are the lowest part of a wave.

          The frequency of a wave, on the other hand, refers to the number of waves produced by a source each second. It could also denote the number of waves that pass a certain point each second. The unit of frequency is hertz (Hz). Kilohertz, megahertz and gigahertz are used when the waves have high frequencies.

          Both frequency and wavelength are related to the pitch of a sound, meaning they determine how high or low a sound is going to be. The greater the frequency, the shorter is the wavelength and, higher the pitch. 

          Put it simple, amplitude is the height of the peaks of a sound wave.

          Let’s try to understand the concept with the example of sea. Sometimes when you visit it, the sea looks calm. But sometimes, it gets rough with huge waves. As the waves develop, we can see some parts dipping down lower than the normal surface of water, and others rising higher than the same. The distance between this dip and the rise of a wave from the calm surface is generally referred to as amplitude.

          In the context of sound, amplitude is the size of vibrations, determining how loud a sound is to be. We know for a fact that larger vibrations create louder sounds.

         Intensity, as some of you might know already, describes the amount of energy in a sound. For example, a pistol shot has more intensity and produces more sound compared to a cork being pulled off a bottle.