Do our ears or brains gradually adapt to noise pollution?

Do our ears or brains gradually adapt to noise pollution?

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Having lived in various places all over the world for the past 9 years of my life, one thing stood out to me throughout this time, and now in particular. From a quiet place on the countryside in Sweden, I moved to Manchester for my studies. When I first arrived there, I felt the city was very noisy, a feeling which gradually reduced as I presumably got used to the noise levels there. From Manchester I moved over to Saitama in Japan, an enormous city right next to Tokyo with a considerable amount of noise during the day, and buildings that have little to no sound insulation. With the exception of particularly loud noises, I again adapted to the sound levels in the country, which at the time, I felt was no more than a natural response in terms of how much attention we pay to the noise. If I'm distracted by work or other activities, I have little reason to dwell on the sounds of driving cars and talking people.

The thing I couldn't explain purely by the 'paying attention' argument however was when I moved back to the Netherlands, to an apartment with excellent sound insulation. My apartment is located in front of a somewhat larger road, and cars pass by almost consistently. However, when I moved in I could barely hear these cars driving past, something that stood out to me as fairly pleasant. I thought a little bit of ambient music would kill the sound of these vehicles driving past altogether.

Now skip ahead one month, and I can hear the cars almost as if I'm standing next to them, an exaggeration of course, but the sound is much clearer than it was when I moved in. I know that nothing has changed in terms of insulation and I know that no windows are open. Strangely the only thing that appears to have changed is the clarity in which I perceive this noise, as none of the other people whom I've asked seem to share the same opinion (that is, that the noise has grown louder). This made me wonder - does our hearing adapt to noise pollution, and if so, how does it work?

This is a fascinating case of sensory adaptation and neural adaptation. Another example of this would be when you stop smelling something after being exposed to it for long periods of time (as you probably know, this "long period of time" happens to only be a few minutes). A great representation of this happening with the nerves in the skin was done by Georg Meissner:

This image is from

When stimulus is applied, these nerves begin rapidly sending messages to the brain in the alarm period. The rate of these signals slowly start to decrease over time in the resistance period until they finally reach exhaustion and stop completely in, of course, the exhaustion period. Keep in mind that the time it takes for all this to happen varies greatly upon what type of cell it is (obviously olfactory cells have a much shorter exhaustion time than, say, hair cells (hearing cells)). After these cells have had a chance to recover (more like recalibrate actually), we can begin to hear/smell/feel/taste again.

I hope this helps.

Very quickly and totally from the top of my head: Traffic noise is in many cases dominated by low frequencies, with the whole spectrum somewhat similar to a distorted 1/f function, with a few tonal peaks for exhaust noise and tyre/tread sounds. Now add the structure you are living in: "excellent sound insulation" in the EU is (still) dB(A)-focused, meaning architects and planners are aiming for a "wow" effect in noise reduction by eliminating that what's easy to eliminate - high and mid frequencies, ignoring mostly the low (and energy-rich) frequencies, which are incidentally the ones the A-weighing of noise is (historically) ignoring as well. As a result, you are basically living in what's known as a low-pass filter, one that is also "drawing" tonal peaks (resonances, room nodes) out of that low-frequency noise mixture. At first, your cochlea's short-term adaption mechanisms will do their job well and tone down signals that are not meaningful (MOC reflex).

Over time however, the presence of low-level tonal, continuous sounds can damage ("wear out") a specific sensor type necessary for this reflex to work. As a result, even inaudible LFN noise can, over time, lead to a distal sensitization effect. In many cases the culprit is actually not the traffic noise itself, but HVAC installations like heat pumps, A/Cs and gas turbines. The effect of "I can hear too much" (being aware of noises) as a result of sub-threshold LFN-exposure is known in the medical literature as a symptom of VAD stage I / II and in fact quite common in the urban population. Certain medications (Gentamycine, cis-platines) as well as organic solvents (acetone) and some disinfectants can speed up this process, which is non-reversible and poses a risk factor for suffering atypical (early onset) hearing loss later on… The "I hear too much" effect has been quite a solid indicator of long-term, low-level IS/LFN noise pollution.

To be on the safe side and to rule out a sub-threshold LFN-problem, you should an seek medical advice. Sources:

Bakay, W.M.H., Anderson, L.A., Garcia-Lazaro, J.A., McAlpine, D. and Schaette, R., 2018. Hidden hearing loss selectively impairs neural adaptation to loud sound environments. Nature communications, 9(1), p.4298.

Branco, N., 2005. Clinical stages of vibroacoustic disease (VAD) for health professional continuous research. Mat. 12th int. sym. Lisbon, p.145.

Burt, T., 1996. Sick building syndrome: acoustic aspects. Indoor and Built Environment, 5(1), pp.44-59.

Ebner, F., Eulitz, C. and Möhler, U., Approaches for a comprehensive determination and assessment of infrasound effects in Germany. DAGA 2013 Conference Paper.

Findeis, H. and Peters, E., 2004. Disturbing effects of low frequency sound immissions and vibrations in residential buildings. Noise and Health, 6(23), p.29.

Kugler, K., Wiegrebe, L., Grothe, B., Kössl, M., Gürkov, R., Krause, E. and Drexl, M., 2014. Low-frequency sound affects active micromechanics in the human inner ear. Royal Society Open Science, 1(2), p.140166.

Paulin J, Andersson L, Nordin S. Characteristics of hyperacusis in the general population. Noise Health 2016;18:178-84

Waye, K.P., Clow, A., Edwards, S., Hucklebridge, F. and Rylander, R., 2003. Effects of nighttime low frequency noise on the cortisol response to awakening and subjective sleep quality. Life sciences, 72(8), pp.863-875.

Things You Need To Know About How Noise Pollution Affects You

June 21, 2020//-Many of us know of the three major types of pollution: air, water and land. But, rapid urbanization in the past decades changed our world. There are now other environmental factors we have to contend with.

The world, for instance, is a much noisier one now. Gone are the nights of near absolute silence, with you waking up to the sound of that overenthusiastic rooster. Instead, it’s more likely that the noise outside your home never really stopped.

What Is Safe?

Noise refers to all sounds that are undesirable or unpleasant. Sound (or noise) intensity is measured in logarithmic decibel (dB) units. The term “logarithmic” just means that numbers on the scale are not the same distance apart. The decibel scale caters to human audibility.

  • Near total silence equates to 0 dB
  • A sound 10 times more powerful than that is 10 dB
  • A sound 100 times more powerful than near total silence is 20 dB (not 100 dB!)
  • A sound 1000 times more powerful than near total silence is 30 dB
  • … and so on…

The higher the decibel level, the louder the noise, and the more damage to your hearing!

The safe limit recommended by experts at the US Environment Protection Agency is 70 dB. Below this level, even prolonged exposure is unlikely to cause hearing loss.

But, many of us are exposed to much greater intensities on a daily basis. Any level at or above 85 dB is likely to cause damage over time. The louder the sound, the shorter the amount of time is needed to cause damage.

Effects On Health

Hearing Problems

According to the World Health Organisation (WHO), exposure to excessive noise is the 2nd major cause of adult-onset hearing loss. This is largely preventable. Excessive noise can overstimulate and damage the sensory cells of the inner ear.

Hearing loss can occur either gradually or suddenly, depending on how long and how loud the noise. Victims often first notice having problems understanding speech in noisy situations. These difficulties can be worse in fluctuating noise. Over time, challenges in interacting with others may lead to social isolation.

Besides, hearing loss due to noise exposure can predispose you to tinnitus. Tinnitus refers to the experience of detecting sound when it is in fact absent. This happens when the central nervous system is faulty and sends false signals to the brain. Why does it do that?

When there is a stimulus (such as sound), the nearest sensory cell that experiences it gets excited. This excited sensory cell fires signals to the nerve cell right next to it, which then “passes the message” closer and closer to the brain. Now think of this signaling as a long chain of people holding hands.

The first person reacts to the stimulus and squeezes the next person’s hand to pass the message. Eventually the message is received by the last person (the brain).

Squeezing stops when there is no more stimulus to excite the first person. But, imagine if the stimulation was excessive. Some people may be so used to squeezing hands, they forget to stop – even when the stimulus is long gone!

People who suffer from tinnitus describe hearing “ringing”, “buzzing”, “whistling” and other noises. Tinnitus can reduce our ability to concentrate and relax. A frequent sequelae is the development of anxiety and depression.

Long-term noise exposure may also increase risk for noise sensitivity. If severe, this condition can be highly debilitating in our noisy world.

Cardiovascular Effects

The cardiovascular system is also known as the circulatory system. It consists of the heart and a closed system of blood vessels. The heart is an incredible muscle that pumps blood to the entire body, supplying all its parts with nutrients and helping with the removal of waste.

But, this self-regulating system is not immune to the threats from our environment. Scientists have found links between noise exposure and cardiovascular disease. They suggest that acute noise exposure can

Chronic noise exposure further results in

  • Higher blood lipid concentrations
  • Higher blood viscosity
  • Higher blood glucose concentrations

These can put a strain on the cardiovascular system, resulting in risk of hypertension and atherosclerosis. More severe events like heart attack and stroke tend to occur with these risk factors.

Unfavorable Pregnancy Outcomes

Pregnancy is one of nature’s most amazing feats. It also places a lot of stress on the mother’s body, with all that growing happening at breakneck speed! Researchers looked at nearly 270,000 deliveries in Canada.

Their finding? Women exposed to environmental noise pollution had a higher risk of preeclampsia. This is a pregnancy complication that can lead to maternal and infant death if untreated.

Signs include hypertension and damage to another organ system (usually liver and kidneys). Poorer blood flow to the placenta also may lead to preterm births and smaller babies. It is only logical to cut as many risk factors as possible. We need to protect mothers and their babies during this vulnerable time.

Sleep Disturbance

While sleeping, our conscious minds are rarely fully aware of our external environment. But that does not mean that our physical bodies are equally unperturbed.

Our bodies continuously experience, evaluate and react to environmental sounds (even if we are not aware of it). Awakenings are relatively rare in most people, because sleep is “actively protected” by our bodies.

Most of us are able to adapt quickly to new noises and new sleeping environments. But, the physiological reactions do not adapt. This is demonstrated by effects such as changes to heart rate and increased motility.

Nature provided us with some safeguards to ensure we sleep. But, sleep can still be disturbed if noise levels exceed a certain threshold.

The WHO came up with a summary of effects and threshold levels for effects. It recommends that sound levels be kept at a maximum of 40 dB for the long-term prevention of noise-induced health effects during sleep.

Poor sleep is known to result in a whole host of downstream effects. Reversible, short-term effects include sleepiness and moodiness. But these can morph to more dangerous problems such as depression and violence. And it doesn’t just affect you. If noise is affecting your home, your loved ones will be affected too. Imagine a bunch of irritable and sub optimally-functioning humans living under 1 roof!

This table by Lavie, Pillar and Malhotra (2002) summarises the other effects of poor sleep.

Cognitive And Learning Disorders

Children may be particularly vulnerable to their environment. This may be because they cannot articulate discomfort well. Their relatively small size also means they are more heavily exposed to pollutants in proportion to their body weight. Thus, there is keen interest to investigate the effect of various pollutants on this at risk group.

Researchers looked at close to 3000 European school children who attend schools near major airports. The inevitable chronic plane noises were found to impair cognitive development.

Many of these children had greater difficulty gaining knowledge and problem solving skills. Reading comprehension, in particular, was challenging. Another study conducted in the UK also found that children fared poorer in similar environments.

These children had poorer recognition memory, conceptual recall memory and information recall memory. In all, more than 20 studies found that places with high noise levels are not conducive for learning.

Behavioral Problems

Hyperactivity refers to continuous activity, impulsiveness, difficulty concentrating, aggressiveness and being distracted easily. Other typical hyperactive behaviours include fidgeting, wandering and talking too much.

Children who live near airports in the Netherlands, Spain and UK were found to be more hyperactive. In Germany, road traffic noise exposure in 10 year olds also caused hyperactivity.

In Asia, close to 1000 elementary and middle-school children in South Korea were evaluated. It was found that noise was associated with behavioural problems. With higher noise exposure, parents reported that their children displayed more:

  1. Aggressive behavior
  2. Anxious / depressed behaviour
  3. Attention Problems
  4. Rule-breaking behavior
  5. Somatic complaints
  6. Social problems
  7. Thought problems
  8. Withdrawal / depression

These behavioral issues in children do not end with childhood or the adolescent years. Such children usually have poorer social skills, self-confidence, and poorer relationships with peers.

There could be long-term implications for educational achievement and occupational opportunities as adults. And that is a compelling reason to nip such problems in the bud!

It’s hard to imagine that noise can have such an effect on our health, well-being and lives. Noise pollution crept up on us insidiously. It also doesn’t help that we cannot “see” noise. But let’s imagine for a minute that every sound you hear right now is a piece of garbage. How large is that garbage pile around you? It’s time to get to work clearing the trash!

Noise and human hearing

The inner ear of humans (and other vertebrates) contains a snail – shaped structure called a cochlea that is lined with thousands of microscopic hairs. When sound vibrations enter the cochlea, they cause the tiny hairs to move back and forth. If strong vibrations blast into the cochlea, the hairs can be flattened and damaged. The damage usually results in some degree of hearing loss.

Sound is measured in decibels (dB). Zero dB represents the quietest sound that a healthy human can hear. One hundred dB equals a noise that is 10 billion times as intense as one dB. Brief exposure to more than 110 dB can damage ears immediately prolonged exposure to more than 85 dB can damage ears gradually.

Examples of decibel – level sounds that one may encounter in modern life are as follows:

  • Quiet library or soft whisper — 30 dB,
  • Normal conversation — 50 to 60 dB,
  • Busy traffic or noisy restaurant — 70 dB,
  • Subways, heavy city traffic, alarm clock at 2 ft (61 cm), or factory noise — 80 dB,
  • Noise in industrial plants, or call centers — 90 dB,
  • Train traveling 45 mi (28 km) per hour — 93 dB,
  • Chain saw, stereo headphones, night club or pneumatic drill — 100 dB,
  • Loudest sound that can be tolerated by the human ear — about 120 dB,
  • Sound at a rock concert in front of speakers, sandblasting, or thunderclap — 120 dB,
  • Gunshot blast or jet plane — 140 dB,
  • Automobile drag race — 171 dB, and
  • Sound at a rocket launching pad — 180 dB.

As noted, the most powerful sounds that humans encounter include jets taking off, loud amplified music, gun shots, and chain saws. Just a single exposure to these sounds can damage human ears.

Humans also damage ears if they are exposed to noises that are less loud, but that are heard more often. For example, office workers who daily endure noise from telephones and loud machines may suffer some hearing loss over time. Workers in loud factories also experience hearing loss.

People can even hurt their hearing when playing. Motorboats, motorcycles, and snowmobiles all make loud noises likely to hurt ears. Playing loud music on a personal stereo can also damage hearing. If someone near can hear the music someone else is playing on their personal stereo, then that person is probably causing noise pollution for others and hearing loss for themselves.

Noise hurts more than just hearing. When people are exposed to loud noise, bodies react as if in danger. Physiological responses to noise include increased heart rate, stress, eye conditions, muscle tension, elevated cholesterol levels and hormone secretion, and of course high blood pressure even migraines can be induced by noise. Noise also impairs concentration. Studies have shown that children ’ s learning and achievement can be also be affected by exposure to noise. Noise over 55 decibels can disrupt sleep and produce aggression if it is uninvited and persists long enough. While such a situation might be acceptable for a short time, millions of people around the world live with excessive noise every day and night.

A noise level of 75 decibels generates high levels of stress in most people. Tinnitus, or ringing in the ear, may occur at 80 decibels. The 100 decibels regularly encountered in nightclubs can cause ear damage after only fifteen minutes. Noise can also induce mental states that lead to suicide and homicide. In Great Britain, anti – noise campaigners are keeping a count of the number of crime – related deaths that occur each year traceable to a response to noise.

Is human noise pollution affecting our sharks?

Some sharks are migratory and can potentially leave a disturbed area, for example great whites (Carcharodon carcharias), tigers (Galeocerdo cuvier) and whale sharks. Credit: iStock

Human made noise, also called anthropogenic noise, is rising in many environments due to the increase in transportation and the exploration for and exploitation of energy sources.

North Western Australia, in particular as the most active area of the country in terms of oil and gas exploration and coastal construction activities, is filling WA's coastline with added background noise.

In the extreme, anthropogenic noise can destroy the vulnerable sensory tissues, in the inner ear and the lateral line systems of fishes.

This may ultimately lead to death if the animals lose their ability to hear or detect hydrodynamic changes.

Noise can also be a source of acute or chronic stress, which may affect behavioural and sensory functions.

Besides, a loud sound can mask important biological sounds, essential to marine organisms in communication, finding prey and mates and detecting predators.

More than 100 species of sharks and rays live in WA waters, ranging from the tiny pygmy shark (Euprotomicrus bispinatus) to the iconic whale shark (Rhincodon typus), the world's biggest fish.

Sharks, like bony fishes, possess an inner ear and a lateral line, which are sensitive to underwater vibrations and sounds.

Brown banded bamboo shark. Credit: Paul Ricketts/UWA

Compared to marine mammals, sharks have a very narrow hearing range but are known to be particularly sensitive to very low frequencies.

This hearing range overlaps with most of the anthropogenic sound produced by seismic airgun arrays, dredging, pile driving and shipping.

Some sharks are migratory and can potentially leave a disturbed area, for example great whites (Carcharodon carcharias), tigers (Galeocerdo cuvier) and whale sharks.

However most of the species, such as wobbegong (Orectolobidae), bamboo (Hemiscylliidae) and Port Jackson sharks (Heterodontus portusjacksoni), stay in a single location or patch of reef or change habitats only when they reach a critical part of their lifecycle like most reef sharks do.

Sound pollution represents a particular threat for those sedentary sharks, as they would typically not leave the area during a high intensity sound event.

In an effort to fill these vital knowledge gaps, the Neuroecology Group which is part of the UWA Oceans Institute and School of Animal Biology is studying the effects of sounds on sharks.

Our first strategy is to assess their sensitivity to sound such as what frequencies and intensities the different species react to, with electrophysiological techniques in the laboratory.

Assessing the hearing sensitivity of a Port Jackson shark in the lab. Credit: Paul Ricketts/UWA

We will then partner with industry to assess and characterise the different anthropogenic sounds that are 'ensonifying' our waters.

We can then assess the potential overlap, comparing the ambient soundscape with the auditory abilities of local shark species and identify any threats of local sound sources to the local shark populations.

Finally, and most importantly the behaviour of wild animals and their responses to different anthropogenic noise needs to be observed and examined to establish any short- and long-term effects.

It is a big challenge, as we are examining wild animal movement in their natural habitat and needing to observe and quantify their responses before, during and for an extended period after exposure to particular sounds.

However, at this stage, the specific regulation on anthropogenic noise in Australia covers only a few species of marine mammals.

We feel there is a dire need and a responsibility to fill a large knowledge gap, to inform management practises and policy and broaden the regulatory framework to include the effects of noise pollution on a wider range of marine species, including sharks and their relatives.

Brain Training With Music

We all enjoy music though most of us have considered it to be for recreation and relaxation. We have all sensed the power that music possesses that affects our mood but most of us have not considered the possibility that it can actually affect our learning ability nor have we been aware of its ability to open neuropathways in our brain.

Music is not only pleasant to listen to but sound is an important nutrient for the nervous system. An unborn baby can hear its mother’s voice in the womb at 16 weeks—the sound of mother’s voice nourishes and nurtures the baby’s nervous system. .Intrauterine listening is essential as its nurturing sound stimulates brain growth for language development, bonding and attachment. We have all heard of the “Mozart Effect” which involves the use of classical music to train the brain for language development and higher level thinking skills. Just as specific body movements (such as exercises that cross the body midline) and eye exercises re-train the brain, music powerfully re-trains the auditory processing system of a child. There are specific sonic exercises that are designed to strengthen the brain/auditory system just like a physical exercise would strengthen the body.Ear infections can leave a child with a less than optimal ability to perceive sound correctly long after the ear infections have passed which can lead to an auditory processing difficulty and can affect reading, phonics, spelling, and attention. Sometimes this processing weakness can be measured on an audiogram and sometimes it is so subtle that it cannot be measured. It is found that the cilia of the ear—the tiny hairs that are responsible for sound transference that are often damaged with repeated ear infections—can be encouraged to function more efficiently through the use of specific tones and frequencies of sound that are found in certain types of music.50 years ago, Dr. Alfred Tomatis, an ear, nose and throat surgeon from France, discovered that the ear is like a battery that converts sounds into electrical waves that charge the cortex of the brain. He created a system of re-training the auditory system by using specially-treated classical music that is pleasant to listen to. By listening to these specially-treated and recorded albums in the home, he found that this stimulation re-educated the auditory system to function properly. He also found that this auditory brain training helped children in organizing their thoughts, focusing attention, balance, phonics, reading, spelling, and in hearing and understanding oral instructions, particularly in the presence of background noise. His conclusion was that music has the ability to cause both subtle and profound changes in children.

There is a tremendous amount of noise pollution (hair blowers, lawn mowers, traffic, dishwashers, etc.) bombarding our children’s auditory and nervous systems daily. One of the ways we can combat this more destructive noise is to first realize that loud noises are perceived as stressors to the nervous system. We can go a long way in combating this daily assault by simply putting on soft background music throughout the day to help balance both their nervous system and auditory system. There is even specific music designed to help children concentrate with background noise. In classrooms where teachers are aware of this connection and regularly play specially prepared classical music softly in the background during seatwork, children are found to be able to concentrate much better and be more accurate in their work.

  1. Be aware of daily noise pollution in your home. Keep the mechanical noise to a minimum whenever possible. Play classical music softly in the background to reduce the effects of the extraneous noise and enhance learning. Mozart, Bach and Vivaldi are some composers that help with this process.
  2. To enhance listening ability further or to help a child struggling with auditory processing, attention, reading issues, etc., use a listening program of specially-treated music, employing headphones, and a regular schedule designed to gradually re-train the brain to process sound more efficiently.

As a special education teacher and a health professional, I am very aware of the importance of excellent nutrition for maximizing learning ability and reducing the effects of learning disabilities. Knowing that sound is another important nutrient and utilizing it through classical music to train the brain to process sounds more efficiently gives us another avenue to use to help our children. Sound affects us either negatively or positively: we can choose our children’s sound environment every day. We can even choose to use music in specific ways to restore auditory processing and other abilities that have been lost.

The neuroplasticity of the brain is quite amazing. Each decade new methods are being discovered that help heal and retrain the brain to function the way God intended it to function.

There are several programs available that are very helpful to many children:

The information in this article should not be construed as a diagnosis or medical advice. Please consult your physician for any medical condition and before adding supplements or changing a child’s diet.

Dianne Craft has a Master’s Degree in special education and is a Certified Natural Health Professional. She has a private consultation practice, Child Diagnostics, Inc., in Littleton, Colorado.

Class 8 Science Chapter 13 Sound

Topics and Sub Topics in Class 8 Science Chapter 13 Sound:

Section Name Topic Name
13.1Sound is Produced by a Vibrating Body
13.2Sound Produced by Humans
13.3Sound Needs a Medium for Propagation
13.4We Hear Sound through Our Ears
13.5Amplitude, Time Period and Frequency of a Vibration
13.6Audible and Inaudible Sounds
13.7Noise and Music
13.8Noise Pollution

Sound Class 8 Science NCERT Textbook Questions

Question 1.
Choose the correct answer.
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids, and gases
(d) solids, liquids, and gases.

Question 2.
Voice of which of the following is likely to have a minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
(c) A man

Question 3.
In the following statements, tick ‘T’ against those which are true and ‘F’ against those which are false.

  1. Sound cannot travel in a vacuum.
  2. The number of oscillations per second of a vibrating object is called its time period.
  3. If the amplitude of vibration is large, the sound is feeble.
  4. For human ears, the audible range is 20 Hz to 20,000 Hz.
  5. The lower the frequency of vibration, the higher is the pitch.
  6. Unwanted or unpleasant sound is termed as music.
  7. Noise pollution may cause partial hearing impairment.

Question 4.
Fill in the blanks with suitable words.

  1. Time taken by an object to complete one oscillation is called _______
  2. Loudness is determined by the ________ of vibration.
  3. The unit of frequency is ________
  4. Unwanted sound is called _______
  5. The shrillness of a sound is determined by the ______ of vibration.

Question 5.
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
No. of oscillation = 40
Total time is taken = 4 seconds

Question 6.
The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Number of vibrations per second = 500

Question 7.
Identify the part which vibrates to produce sound in the following instruments.

Question 8.
What is the difference between noise and music? Can music become noise sometimes?
The type of sound which are unpleasant to listen is known as noise whereas music is a pleasant sound, which produces a sensation.
Yes, music can become noise when it’s too loud.

Question 9.
List the sources of noise pollution in your surroundings.
Following are the major sources of noise pollution:

  • Sound of vehicles
  • Sound of kitchen appliances
  • Sound of bursting crackers
  • Sound of loudspeakers, TV, transistors

Question 10.
Explain in what way noise pollution is harmful to humans.
Noise pollution causes:
(a) Lack of sleep
(b) Anxiety
(c) Hypertension
and these are harmful to health.

Question 11.
Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
I would suggest my parents buy a house three lanes away from the roadside because house on the roadside would be much noisy in both days and night due to running vehicles. Whereas, a house three lanes away would be comparatively quieter as the intensity of noise decreases with the distance between the source and the listener.

Question 12.
Sketch larynx and explain its function in your own words.
Larynx is also known as voice box. It is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for passage of air (Fig. 13.12). When lung force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose.

When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.

Question 13.
Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
The speed of light is more than that of the speed of sound. Thus, due to more speed of light it reaches us before sound. So, lightning is seen earlier and thunder is heard later.

Sound Class 8 Science NCERT Intext Activities Solved

Activity 1 (NCERT Textbook, Page 158)
Take a metal plate (or a shallow pan). Hang it at a convenient place in such a way that it does not touch any wall. Now strike it with a stick (Fig. 13.1). Touch the plate or pan gently with your finger. Do you feel the vibrations? Again strike the plate with the stick and hold it tightly with your hands immediately after striking. Do you still hear the sound? Touch the plate after it stops producing sound. Can you feel vibrations now?

When we touch the pan gently with our finger after striking we feel the vibration. When we hold the pan tightly after striking it, we do not hear the sound. When the pan stops producing sound it also stops vibrating. Thus, we can conclude that vibrating body produces sound.

Activity 2 (NCERT Textbook, Page 758)
Jake a rubber band. Put it around the, longer side of a pencil box (Fig. 13.2). Insert two pencils between the box and the stretched rubber. Now, pluck the rubber band somewhere in the middle. Do you hear any sound? Does the band vibrate?

Yes, we hear the sound on plucking the rubber band. Also, we find that the band is vibrating. Thus, all vibrating bodies produce sound.

Activity 3 (NCERT Textbook, Page 758-759)
Take a metal dish. Pour water in it. Strike it at its edge with a spoon (Fig. 13.3). Do you hear a sound? Again strike the dish and then touch it. Can you feel the dish vibrating? Strike the dish again. Look at the surface of water. Do you see any waves there? Now hold the dish. What change do you observe on the surface of water? Can you explain the change? Is there a hint to connect sound with the vibrations of a body?

On striking the metal dish we hear sound and on touching it we feel the dish vibrating. Striking the dish with water we see circular wave are produced. Thus vibrating object produces sound.

Activity 4 (NCERT Textbook, Page 159)
Take a hollow coconut shell and make a musical instrument ektara. You can also make it with the help of an earthen pot (Fig. 13.4). Play this instrument and identify its vibrating part.

We observed that the vibrating part of the musical instrument ektara is stretched string.

Activity 5 (NCERT Textbook, Page 160)
Take 6-8 bowls or tumblers. Fill them with water upto different levels, increasing gradually from one end to the other. Now take a pencil and strike the bowls gently. Strike all of them in succession. You will hear pleasant sounds. This is your Jaltarang (Fig. 13.5).

We can hear a pleasant sound. This is due to different levels of water in the bowls.
Thus, we find that shorter the length of the vibrating air column, higher is the pitch of the sound produced.

Activity 6 (NCERT Textbook, Page 161)
Take two rubber strips of the same size. Place these two pieces one above the other and stretch them tight. Now blow air through the gap between them [Fig. 13.6(a)]. As the air blows through the stretched rubber strips, a sound is produced. You can also take a piece of paper with a narrow slit and hold it between your fingers as shown in [Fig. 13.6(b)]. Now blow through the slit and listen to the sound.

This activity shows that vocal cords also produce sound in a similar manner when they vibrate.

Activity 7 (NCERT Textbook, Page 161)
Take a metal or glass tumbler. Make sure that it is dry. Place a cell phone in it. Ask your friend to give a ring on this cell phone from another cell phone. Listen to the ring carefully.
Now, surround the rim of the tumbler with your hands (Fig. 13.7). Put your mouth on the opening between your hands. Indicate to your friend to give a ring again. Listen to the ring while sucking air from the tumbler. Does the sound become fainter as you suck air?
Remove the tumbler from your mouth. Does the sound become loud again?

We observed that sound becomes fainter than earlier when we try to suck air. But when we remove tumbler from our mouth the sound again becomes loud. Thus, sound needs a medium to travel.

Activity 8 (NCERT Textbook, Page 162)
Take a bucket or a bathtub. Fill it with clean water.
Take a small bell in one hand. Shake this bell inside the water to produce sound. Make sure that the bell does not touch the body of the bucket or the tub. Place your ear gently on the water surface (Fig. 13.8). Can you hear the sound of the bell? Does it indicate that sound can travel through liquids?

We can hear the sound of the bell which indicates that sound can travel through liquids.

Activity 9 (NCERT Textbook, Page 162)
Take a metre scale ora long metal rod and hold its one end to your ear. Ask your friend to gently scratch or tap at the other end of the scale (Fig. 13.9).
Can you hear the sound of the scratching? Ask your friends around you if they were able to hear the same sound?

Yes, we find that we can hear the sound of the scratch. But, the people standing around us cannot hear the same sound or we can say that it is limping not audible to them.

Activity 10 (NCERT Textbook, Page 163)
Take a plastic or tin can. Cut its ends. Stretch a piece of rubber balloon across one end of the can and fasten it with a rubber band. Put four or five grains of dry cereal on the stretched rubber. Now ask your friend to speak”Hurrey, Hurrey”from the open end (Fig. 13.10). Observe what happens to the grain. Why do the grain jump up and down?

The grain jump up and down because of the vibration caused underneath the stretched rubber. Thus when sound waves fall on the eardrum, it starts vibrating back and forth rapidly.

Activity 11 (NCERT Textbook, Page 164-165)
Take a metallic tumbler and a tablespoon. Strike the tablespoon gently at the brim of the tumbler. Hear the sound produced. Now bang the spoon on the tumbler and hear the sound produced again. Is the sound louder when the tumbler is struck hard?
Now suspend a small thermocol ball touching the rim of the tumbler (Fig. 13.11). Vibrate the tumbler by striking it. See how far the ball is displaced. The displacement of the ball is a measure of the amplitude of vibration of the tumbler.
Now, strike the tumbler gently and then with some force. Compare the amplitudes of vibrations of the tumbler in the two cases. In which case is the amplitude larger?

The sound produced is louder when the tumbler is struck hard. The amplitude of vibration of the tumbler is larger when the glass is struck hard.Thus the loudness of sound depends upon the amplitude of vibration.

NCERT Solutions for Class 8 Science Chapter 13 – 1 Mark Questions and Answers

Question 1.
Choose the correct answer. Sound can travel through

Solids, liquids and gases.

Question 2.
Voice of which of the following is likely to have minimum frequency ? [NCERT]

Question 3.
Identify the part which vibrates to produce sound in the following instruments. [NCERT]

Question 4.
In the following statements, tick ‘T’ against those which are true and ‘F’ against those which are false. [NCERT]

  1. Sound cannot travel in vacuum. (T/F)
  2. The number of oscillations per second of a vibrating object is called its time period. (T/F)
  3. If the amplitude of vibration is large, sound is feeble. (T/F)
  4. For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
  5. The lower the frequency of vibration, the higher is the pitch. (T/F)
  6. Unwanted or unpleasant sound is termed as music. (T/F)
  7. Noise pollution may cause partial hearing impairment. (T/F)

Question 5.
Fill in the blanks with suitable words. [NCERT]

  1. Time taken by an object to complete one oscillation is called …………
  2. Loudness is determined by the ………….. of vibration.
  3. The unit of frequency is ……………
  4. Unwanted sound is called …………….
  5. Shrillness of a sound is determined by the …………….. of vibration.

Question 6.
Define vibration.
Vibration is the to and fro or back and forth motion of an object.

Question 7.
Which part of the human body is responsible for producing sound ? [NCT 2011]
In humans, the sound is produced by the voice box or larynx

Question 8.
What is the length of vocal cords in men ?
The vocal cords in men are about 20 mm long.

Question 9.
Can sound travel in vacuum ?
No, sound cannot travel in vacuum.

Question 10.
What is meant by oscillatory motion ?
The to and fro motion of an object is known as oscillatory motion.

Question 11.
Define frequency.
The number of oscillations per second is called the frequency of oscillation.

Question 12.
Define 1 hertz.
A frequency of 1 hertz means one oscillation per second.

Question 13.
How are frequency of a sound and pitch related ?
If the frequency of vibration is higher then the sound has a higher pitch.

Question 14.
Whose voice has a higher frequency – man or woman ?
The voice of woman has higher frequency.

Question 15.
What is range of audible sound ?
Sound of frequency 20 Hz to 20,000 Hz is the audible range.

Question 16.
Which animal can hear sounds of frequencies higher than 20,000 Hz ?
Dogs can hear frequencies higher than 20,000 Hz.

Question 17.
What is meant by base loudness level ?
The base loudness level is defined as that loudness of sound that the human ear can just perceive.

Question 18.
What is meant by noise pollution ?
Presence of excessive or unwanted sound in the atmosphere is called noise pollutipn.

Question 19.
If the frequency of a sound is below 20 Hz, will it be audible to human beings ?
No, it will not be audible.

Question 20.
In which state of matter does sound travel the

Question 21.
What happens to sound when it strikes a surface ?
Sound gets reflected on striking a surface.

Question 22.
Why do we hear the sound of the hom of an approaching car before the car reaches us ?
This happens because the speed of sound is much greater than the speed of the car.

NCERT Solutions for Class 8 Science Chapter 13 – 2 Mark Questions and Answers

Question 1.
The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration ? [NCERT]
Time taken for 500 vibrations = 1 second
Time taken for 1 vibration = 1/500 second.
∴ Time period = 1/500 second.

Question 2.
How do plants help in reducing noise pollution ?
Plants absorb sound and so help us in minimizing noise pollution.

Question 3.
How can we control the sources of noise pollution ?
We can control noise pollution by designing and installing silencing devices in machines.

Question 4.
How can a hearing impaired child communicate ?
A hearing impaired child can communicate effectively by using sign language.

Question 5.
If the amplitude increases 3 times, by how much will the loudness increase ?
If the amplitude increases three times, the loudness will increase by a factor of 9.

Question 6.
The frequency of a given sound is 1.5 kHz. How many vibrations is it completing in one second ?
Frequency = No.of vibrations/time
∴ No. of vibrations = Frequency x time = 1.5 x 1000 x 1 = 1500 vibrations

Question 7.
Which characteristic of a vibrating body determines

Question 8.
Why do we not hear echoes in our ordinary surroundings ?
We do not hear echoes in our ordinary surroundings because the distance to hear echo should be more than 17 m.

Question 9.
We cannot hear the sound of the exploding meteors in the sky, though we can see them. Why ?
Sound cannot travel through vacuum. In space there is vacuum. Light can travel through vacuum, so we can see the exploding meteor but cannot hear the explosion.

Question 10.
We can hear the supersonic jet planes flying. How ?
The supersonic jet planes fly in the air. Since sound can travel through air, we can hear then flying.

Question 11.
What are vocal cords ? What is their function ? [NCT 2011]
The larynx has a pair of membranes known as vocal cords stretched across their length. The vocal cords vibrate and produce sound.

Question 12.
When does a thud become music ?
When thuds are repeated at’regular intervals, it becomes music, e.g., beating of drums or wood.

Question 13.
How do birds and insects produce sound ?
Birds chirp with the help syrinx in their wind pipe. Insects produce sound by flapping their wings.

Question 14.
What is the function of eusfachian tube in human ear ?
The vibrations of the spoken words reach our ears through eustachian tubes.

  1. In our body which part of the ear receives sound waves ?
  2. What may happen if the eardrum is absent from our ear ?
  1. Pinna helps in receiving sound waves.
  2. If the eardrum is absent we would not be able to hear.

Question 16.
Can a hearing impaired child speak ? If not why ?
A child having hearing impairment can not speak because if he is able to hear, he will leam to speak.

Question 17.
Give an example each of:

  1. stringed instrument
  2. percussion instrument
  3. wind instrument
  4. striking instrument

Question 18.
Can sound travel through water ? How do whales communicate under water ?
Yes, sound can travel through water. Since sound can travel through water, the whales can communicate with each other.

Question 19.
How is the pressure variation in a sound wave amplified in human ear ?
The pressure variation in a sound wave causes vibrations in the eardrum. These vibrations are amplified several times by the three bones. (The hammer, anvil and stirrup).

Question 20.
How is that you can hear a friend talking in another room without seeing him ?
Sound can travel in all directions and around comers. Light cannot travel around comers. Therefore, we can hear a friend talking in another room but cannot see him.

NCERT Solutions for Class 8 Science Chapter 13 – 3 Mark Questions and Answers

Question 1.
List sources of noise pollution in your surroundings. [NCERT]
The major sources of noise pollution are sounds of vehicles, explosions, machines, loudspeakers.

Question 2.
What are the effects of noise pollution ?
Due to noise pollution a person may suffer from lack of sleep, hypertension and anxiety. If a person is exposed to noise continuously he may get temporary or permanent deafness.

Question 3.
How can the noise pollution be controlled in residential area ?

  1. The noisy operations must be conducted away from residential areas.
  2. Noise producing industries should be set away from such areas.
  3. Use of automobile horns be minimized.
  4. TV and music systems should be run at lower volumes.

Question 4.
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency. [NCT 2011, NCERT]
40 vibrations in 4 seconds.
10 vibrations in 1 second
Frequency =10 vibrations/sec. or 10 Hz.
∴ Time period = 1/10 sec.

Question 5.
Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy ? Explain your answer. [NCERT]
I would advise my parents to buy the house three lanes away from the roadside because there the noise from automobiles would be much less.

Question 6.
What happens when we pluck the strings of a sitar ?
When we pluck the strings of a sitar, the whole instrument vibrates and the sound is heard.

Question 7.
Why is the voice of men, women and children different ?
The voice of men, women and children are different because the length of vocal cords are different. The length of vocal cords is longest in men and shortest in children.

Question 8.
How are we able to hear sound ?
The eardrum is like a stretched rubber sheet. Sound vibrations make the eardrum vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we are able to hear.

Question 9.
What sources in the home may lead to noise ?
Television and transistor at high volumes, some kitchen appliances, desert coolers, air conditioners all contribute to noise pollution.

Question 10.
What is the-difference between noise and music ? Can music become noise sometimes,?
Unpleasant sounds are called noise.
Music is a sound which produces a pleasing sensation.
If the music is too loud, it becomes noise.

Question 11.
Draw a labelled diagram showing the structure of the human ear.

Question 12.
What is the function of:

  1. The external ear helps us in receiving the sound waves and directing them to the eardrum.
  2. The internal ear has cochlea which is filled with a fluid and having tiny hair cells inside. The hairy cells change the sound vibrations into nerve impulse which travels to the brain.
    The internal ear also helps us in balancing the body.

Question 13.
Give some suggestions by which we can keep our ears healthy.

  1. Never insert any pointed object into the ear. Tt can damage the eardrum and make a person deaf.
  2. Never shout loudly in someone’s ear.
  3. Never hit anyone hard on their ear.

Question 14.
Can you hear the sound on the moon ? Explain.
We cannot hear the sound on the moon because sound requires a material medium to travel. On the moon there is no atmosphere and sound cannot travel in vacuum.

Question 15.
What are ultrasounds ? How are they useful to us?
Sound having frequency higher than 20kHz is known as ultrasound, is used for

  • detecting finer faults in metal sheets.
  • scanning and imaging the body for stones, tumour and foetus.

NCERT Solutions for Class 8 Science Chapter 13 – 5 Mark Questions and Answers

Question 1.
Sketch larynx and explain its function in your own words. [NCERT]
We produce sound in the larynx of our throats. The larynx has two vocal cords, which are folds of tissue with a slit like opening between them. When we speak, air passes through the opening and the vocal cords vibrate to produce sound.

Question 2.
Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why ? [NCERT]
The speed of light is more than the speed of sound. Therefore, even though thunder and lightning take place simultaneously, we see the lightning earlier.

  1. SONAR refers to Sound Navigation and Ranging.
  2. The principle of reflection of sound is used in SONAR.
  3. SONAR is used to measure the depth of the ocean. Ultrasonic waves are sent from the ship down into the sea. They are received back after reflection from the sea bed. The depth is calculated by noting the time period.

Question 4.
What is the use of ultrasound in medicine and industry ?
Use of ultrasound in medicine :

  • For scanning and imaging the body for stones, tumour and foetus.
  • For relieving pain in muscles and joints.

Use of ultrasound in industry :

  • For detecting finer faults in metal sheets.
  • In dish washing machines where water and detergent are vibrate with ultrasonic vibrators.
  • For homogenising milk in milk plants.

Question 5.
What is a sonogram ? Why is it preferred to X-rays ?
Sonogram is image of the internal organs. Ultrasound can pass through the human body and are reflected back. The reflections are recorded by computer and images are generated on the screen.
Sonogram is not harmful and is therefore used for studying the foetus or stone or tumor in the organs. On the other hand, X-rays can be harmful if humans are exposed for longer time.

  1. Name a property of sound which is
    (i) similar to the property of light.
    (ii) different from that of light.
  2. Why do some people have hearing impairment ? How do they communicate with others ?
  1. (i) The property of sound similar to light is that in both reflection takes place.
    (ii) Sound can travel around comers but light cannot.
  2. Some people suffer from hearing impairment because their ear drum is damaged or absent. This can be from birth or may occur later on. Such people communicate with “sign language”. They can also use “hearing aids”.

NCERT Solutions for Class 8 Science Chapter 13 MCQs

Question 1.
The maximum displacement of a vibrating body on either side of its mean position, is known as its
(a) Frequency
(b) Loudness
(c) Amplitude
(d) Pitch

Question 2.
The frequency of a given sound is 1.5 kHz. The vibrating body is
(a) completing 1,500 vibrations in one second.
(b) taking 1,500 seconds to complete one vibration.
(c) taking 1.5 seconds to complete one vibration.
(d) completing 1.5 vibrations in one second

Question 3.
A given sound is inaudible to the human ear, if
(a) its amplitude is too small.
(b) its frequency is below 20 Hz.
(c) its frequency is above 20 kHz.
(d) it has any of the three characteristics listed above.

Question 4.
Sound can propagate
(a) through vacuum as well as gases
(b) only through gases and liquids
(c) only through gases and solids
(d) any of the three states of the matter.

Question 5.
When lightning and thunder take place, they
(a) occur together and are also observed together.
(b) occur one after the other but are observed together.
(c) occur together but the thunder is observed a little after the lightning.
(d) occur together but the thunder is observed a little before the lightning

Question 6.
Soundshaving frequency more than 20 Hz are called
(a) Infrasonic
(b) Supersonic
(c) Ultrasonic
(d) None of these

Question 7.
Hertz is the unit of
(a) Amplitude
(b) Frequency
(c) Pitch
(d) Wavelength

Question 8.
Loudness of sound is expressed in
(a) Hertz
(b) Decibel
(c) Seconds
(d) None of these

Traffic noise is dangerous for your health: Solutions exist for dense cities

Traffic noise is the second biggest environmental problem in the EU, according to WHO. After air pollution, noise is affecting health the most. But legislation regarding noise pollution is insufficient. A new report shows how negative health effects of noise can be reduced. Several means are easiest to apply in dense cities.

Most of us are not aware that cars today produce as much noise on the outside as they did 40 years ago. However, heavy vehicles have become somewhat quieter. The number of people exposed to noise pollution in our cities remains high. Traffic noise is today linked to stress-related health problems such as stroke and heart disease.

"In recent years, the scientific basis for assessment has broadened considerably. But the legislation to protect residents of unhealthy noise levels is completely inadequate," says Tor Kihlman, Professor Emeritus of Applied Acoustics at Chalmers.

Last fall, Tor Kihlman and Wolfgang Kropp initiated a meeting between international experts from the automotive industry, universities and government agencies in Innsbruck to discuss technical possibilities to achieve better urban environments. A summary report from the meeting is now available, see below.

No simple technical solution exists for solving the traffic noise problem -- neither at the source nor for preventing noise from reaching ears. In order to achieve improvements, concerted actions from everyone involved are required, but such coordination of actions is lacking today. The division of responsibilities is unclear, says Tor Kihlman.

"Many of the needed measures are ideal for implementation in dense cities. They are often in line with what is required to tackle climate change. Here are double benefits to point to," says Tor Kihlman, mentioning three examples: the procurement of quiet public transport, reduced speed, and the usage of buildings as as effective noise barriers, through good urban planning.

The new report describes the first steps needed, politically, for society to move towards substantially reduced health effects caused by traffic noise.

"The problems with traffic noise from roads cannot be satisfactory resolved by only taking actions at the source of the noise, not with foreseeable technology. Therefore, the report is also covering planning and construction measures. But today's methods of measuring and describing the noise emissions are neither sufficient nor adequate from the exposed citizens' point of view, says Tor Kihlman.

Listening In

In December 1963, a woman with short curly hair sat behind the wheel of a gray Chevrolet sports wagon as she drove north from Rhode Island, along America’s eastern shore toward Maine. The car was packed with gadgets there were banks of waterproof microphones, spools of cables hundreds of meters long, two-way radios and walkie-talkies, battery packs and generators, a collapsible aquarium tank made of canvas, and an aluminum boat strapped to the roof. This was a fast-response mobile listening station, on a mission to find noisy fish. The driver’s name, it just so happened, was Marie Poland Fish. She was usually known as Bobbie.

As director of a research lab at the University of Rhode Island, Bobbie’s work was funded by the U.S. Navy. Back then, the military was keen to know what sounds fish make.

Historically, mariners have reported eerie sounds at sea. Moans, thumps and clanking of chains made many think their ships were haunted. This clamor became a major problem in World War II, when the hydrophones of underwater listening stations could no longer detect the distant whir of ship and submarine propellers. Submariners described all sorts of unidentifiable noises: mild beeping, croaking and hammering, whistling and mewing, coal rolling down a metal chute and the tapping of a stick being dragged along a picket fence. At times, the racket even drowned out the biggest battleships, disabling an important part of wartime surveillance.

Following initial investigations, it became clear that some of the noise came down to waves, wind and tides — but animals were chiefly to blame. Fish were so noisy they triggered underwater bombs, which were supposed to detonate only at the sounds and vibrations of a nearby submarine. There was obvious strategic advantage to be gained from knowing more about the hubbub of sea life, including when and where it was noisiest. That’s where Bobbie Fish came in.

When the war finished, and for the next 20 years, she set out to record and identify these unseen sound-makers, most of them fish. Using hydrophones developed as part of the war effort, she fixed long-term listening stations in rivers and bays to gather ambient sounds of the underwater world. Between 1959 and 1967, a research boat went out every week into Narragansett Bay, off the coast of Rhode Island, and brought back fish to Bobbie’s lab, where she recorded their voices.

In 1970, she co-wrote Sounds of Western North Atlantic Fishes , a book filled with spectrograms that showed the shape and texture of fish sounds. Some of the spectrograms came from the fish Bobbie recorded in Maine’s Boothbay Harbor, like a pollock that was lowered into the canvas tank and made thumping sounds when it was handled its spectrogram shows repeated smears of sound, like a comb dragged through paint. Another Boothbay fish was the grubby, whose spectrogram has two clean lines, one lower- and one higher-pitched, both lasting for four seconds, then repeating for two seconds more. The book also features the voice of an ocean sunfish that was found just outside Narragansett Bay and held in a sea pen. It made rasping grunts like a pig, which became louder and more frequent the more it was handled. A goliath grouper in Puerto Rico let off a tremendous boom whenever it was prodded, producing a spectrogram that looks like a series of short strokes of a soft paintbrush another in the Bahamas stayed quiet, although it did, on one occasion, almost swallow the hydrophone in its enormous mouth.

These findings helped Navy personnel tune out the sounds of fish and once more tune in to the sounds of their enemies. Bobbie had shown it’s not just a few fish species that are noisy, but hundreds of them.

Indeed, fish gnash their teeth to make rasping sounds. Coral reef-dwellers called grunts get their name from the grunting sounds they make by grinding their second set of teeth together at the back of their throats. Porcupine fish rub their toothless jaw bones together, making a sound like a rusty hinge. Sculpins use muscles to rattle their pectoral girdle. The list goes on and on.

The noise we make is not music to animals’ ears

Those of us living in cities are used to the sounds of urban living: traffic, construction, airplanes, your neighbour mowing her lawn. Sure, sometimes we find it annoying, but hey, we can deal with it. But unlike us, noise pollution can be a really harmful thing for animals.

Simply put, noise pollution is the sounds associated with human activity. It tends to be much louder and more frequent than natural sources of noise, and can affect animal behaviour and physiology.

Can you hear me?

Communication is important for animals to find and bond with a mate and social group, defend their territory, and warn against danger, like predators. So what happens when you turn up the noise on animals? You guessed it they can’t hear each other. This makes it hard for them to accomplish all that their communication sets out to do. Some animals can adapt to this, such as songbirds that change their song to a higher pitch, sing more loudly, or change the times at which they sing to avoid peak traffic. However, not all animals can do this, which poses a serious problem for them.

This bird is trying to be heard over the 5pm traffic rush. Source: aloush via Flickr.

Be quiet – You’re stressing me out!

Noise pollution can turn peaceful animals into stressheads. Research shows that loud noise increases cortisol levels (a sign of stress) in animals including seahorses, dogs, goldfish, and even humans. Cortisol reduces growth rates, meaning that stressed animals are smaller animals – and smaller animals are generally more vulnerable out in nature. On the other hand, when I’m stressed I eat more – I guess I’d be safe out in the wild!

Excessive noise can also result in slower growth rates and even increase mortality in fish eggs and embryos – you don’t even need to be born to suffer the pain of noise! And if you are born in the noisy wild, you may have fewer siblings. For example, one study found that birds laid fewer eggs in noisy areas. As well as this, some animals respond to stress by becoming more vigilant and hiding more, meaning they are spending less time foraging and so have lower weight gains.

On the funny side though, one study showed that aquaculture fish exposed to classical music actually grew faster, were higher quality, and spawned more fish. So maybe human noises can have a good side?

Protect these fluffy ears! Source: Eric Kilby via Flickr.

Music to your ears is pain to mine

Probably the most obvious impact of loud noise is damage to your ears. A single, loud noise or prolonged exposure to noise can damage animals’ ears, and may even lead to deafness.

Loud noise doesn’t just hurt animals’ ears. The vibrations from loud noise can lead to tears and ruptures in the swim bladder of fishes. This can be pretty serious because the swim bladder is used not only for sound but also for buoyancy control.

So although you may not be able to control the noise of traffic or construction, maybe next time you’re passing through an animal’s home you’ll remember to keep it down – you’d be helping them out a lot.


Sight, smell, taste, touch and hearing: five senses. Senses connect us to our environment, from keeping us secure to enriching us. We live in a world that gives us the opportunity to experience a wide range of sounds. From nature sounds to machinery from a conversation to music from enjoyable to undesirable noises. Hearing keeps us aware and allows us to communicate. Hearing interacts with conscious and unconscious functions. (Graham and John M. Baguley, 2009) (de Sebastián, 1999)

Some sounds can disturb our nerves and some others can be even harmful. Noise pollution may deteriorate hearing, gradually or suddenly. Sounds, mainly over 85 dB (Lonsbury-Martin and Martin, 2010), can damage the sensitive structures of the inner ear causing noise induced hearing loss (NIHL). Unfortunately, this problem is underestimated there are no physical manifestations that we can perceive, until a frustrating communication problem arises. Hearing impairment is a health issue to which we are all exposed, reflected in a growth in incidence and prevalence. Hearing loss has negative effects on individuals, people who interact with them and even educational or socioeconomic aspects. Highlighting, NIHL is preventable. To understand how do loud noises can damage hearing ability we need to know the normal function of this process. (Haggard, 1982)

  1. Arrival of acoustic stimulus to receptors.
  2. Transduction of stimulus.
  3. Processing electrical signals.

Inner ear

Labyrinth: Bony (perilymph) and membranous (endolymph). Semi-circular canals + Cochlea. Cochlea: Hearing portion of the ear. Receptive cells. Divides sounds according to frequency to activate specific auditory nerve fibres. Non-linear action: amplitude compression of sounds to help auditory nerve codify for various intensities. Active process: records around 50 dB of ear’s sensitivity. (Møller, 2013) Coiled
(2.5 turns) tube, formed by three chambers filled with fluid. Connected at helicotrema à Scala tympani and vestibuli: perilymph Scala media: endolymph (high K+) Oval window: produces pressure wave that travels through scala vestibuli à scala tympani à causes vibration of round window. Scala media: part of membranous labyrinth. Also known as cochlear duct. Contains blood vessels of stria vascularis (producer of endolymph). Embodies Organ of Corti: primary receptor of hearing. (Mala, 2006) Organ of Corti: transforms physical energy into nervous energy –transduction Vibration of structures causing displacement of cochlear fluid à movement of hair cells à electrochemical signals. -Components: key sensory cells (inner and outer hair cells, both with stereocilia at apical surfaces), pillar cells (for rigidity and building the tunnel of Corti that separates inner and outer hair cells) and supporting cells (Deiter’s and Hensen cells). (Graham and John M. Baguley, 2009) (The Open University, 2017)

The receptive cells of the inner ear are known as hair cells. Their name comes from the cilia and stereocilia (or kinocilium, a longer hair) that project from the apex of these cells into the cochlear duct. The apexes of the cilia have protein filaments, which connect to adjacent cilia, associated with ion channels that open with tension.

There are two types of hair cells: Inner Hair Cells (IHC) and Outer Hair Cells (OHC). (Mala, 2006)

Inner Hair cells

About 3500, arranged in one row beneath the tectorial membrane (not attached). Cylindrical shape Sensory transduction. 90-95% of afferent nerves are connected to IHC, providing information about sound stimulation (auditory data) from the ear to the brain (neurotransmitter: glutamate). Steady internal potential: – 45 mV (Owen, 2003b) (Møller, 2013)

Outer Hair Cells

Approximately12000 organized in three to four rows (W or V formation). Located near the centre of basilar membrane. Action depends on sound intensity. Mediate active process of the cochlea à “Cochelar amplifier”.Connected to tectorial membrane by stereocilia. Stereocilia: detect vibrations within the cochlea, composed from actin filaments that generate cross-links between rows. Stereociliary bundles: they open ion channels for K and Ca à converting mechanical into electrical energy. Electromotility: Depolarization leads to contraction in response to mechanical stimuli using prestin (the motor protein). OHC adjust the movement of basilar membrane (amplitude) modifying the stimulation received by IHC, increasing frequency selectivity.Olivocochlear efferent innervation (neurotransmitter: acetylcholine) provides the ability to “fine tune” auditory stimuli. Steady internal potential: -70 mV (Brownell et al., 2018) (Mala, 2006) (Owen, 2003) (Møller, 2013)

Mechanoelectrical transduction

  1. Sound waves travel from outer ear à middle ear (stapes hits oval window and generates a wave through the perilymph inside the labyrinth, flowing through helicotrema until round window) à inner ear (wave travels along the cochlea) * High frequencies: base *Low frequencies: apex
  2. Pressure wave inside the cochlea: Vibration of the perilymph à movement of the basilar membrane à vibration of the Organ of Corti (Hair Cells)à OHCs enhance the movement of basilar membrane à perilymph stimulates the stereociliary bundle towards the kinocilium. With sufficient fluid movement the hairs are deflected and ion channels open up by stretching the tip links. *Mechanical energy
  3. Potassium from endolymph gets into the IHC through ion channels (because of positive electrical charge)àpartial depolarization and propagation of action potential à influx of Ca+ along hair cell body à complete depolarization. *Electrical energy
  4. The positive electrical charge modifies the hair cell membrane à Synaptic vesicles containing neurotransmitter
  5. Neurotransmitter (glutamate) is released from the base of the hair cell à neuron excitation (synapsis) à signals towards brain (Auditory Cortex of the temporal lobe) *Chemical energy (Graham and John M. Baguley, 2009)(Owen, 2003a)

Noise Induced Hearing Loss

Hearing loss: an incerase in tresholds over 25 dB. Type: conductive, sensorineural or mixed. Degree: moderate, mild, severe, profound. Configuration: high/low frequency, bilateral/unilateral, symmetrical/asymmetrical, progressive/sudden and fluctuating/stable . (WHO Media centre, 2014) (American Speech Language Hearing Association, 2016). Sensorineural hearing loss: damage to the inner ear (cochlea) or nerve pathway (Vestibulocochelar nerve CNVIII or Central Nervous System). Causes: illnesses, medication, genetic, aging, congenital or loud noises. (American Speech Language Hearing Association, 2016) (Kari, Wilkinson and Woodson, 2013)

Noise Induced Hearing Loss – damage caused by (loud) noise exposure. It can be the result of regular or single events. It can be permanent or temporary. (Neeraj N, Vardhman and Guru Gobind, 2012) Generally occurs at: frequency of 2-4 kHz (American Hearing Research Foundation, 2012) and intensity 85 dB or more. (American Academy of Otolaryngology–Head and Neck Surgery., 2017) Hair cells are not capable of regenerating. (University of Texas, 2014)

Mechanism of damage

  • Mechanical destruction: changes in hair cells’ rigidity à sensory cells destruction àloss of function
  • Excessive metabolic activity at cellular level (oxidative stress): increased levels of energy needed à elevation in oxygen consumption à production of free radicals in the cochlea à insufficient antioxidant defence à cell death (Krug et al., 2015)
  • Oxidative stress and NIHL: the reviews. Summaries of previous information reporting descriptive information about oxidative stress in hearingloss.
  • Oxidative Stress and Cochlear Damage (Hu and Henderson, 2014) [USA] Oxidative stress is able to generate several cochlear pathogeneses causing inner ear disorders. Antioxidant therapies may be used for treatment. Experimental models and data in human studies support the influence of oxidative stress in inner ear disorders mainly by signalling pathways that produce cellular damage and cell death. The effect of antioxidants needs further verification.
  • Mechanisms of sensorineural cell damage, death and survival in the cochlea (Wong and Ryan, 2015) [USA]: Most of acquired hearing loss cases are caused by irreversible damage of sensorineural tissues of the cochlea. Intracellular mechanisms and survival signalling pathways participate in sensorineural injury. Antioxidants, antiapoptotics and cytokine inhibitors drugs are showing advances but will need further support with evidence-based treatment.
  • Cellular mechanisms of noise-induced hearing loss (Kurabi et al., 2017) [USA]: Intense sounds or noises can lead to temporary threshold shift or residual permanent threshold shift with changes in auditory nerve functions. The main cause of NIHL is injury to cochlear hair cells and pathologies involving synapsis. Hair cell damage generates substrates that lead to the collection of reactive oxygen species and activation of intracellular stress pathways producing apoptosis or necrotic cell death. Damage to cochlear neurons is also involved in NIHL.
  • A comprehensive study of oxidative stress in sudden hearing loss (Gul et al., 2017) [Turkey]: There is an oxidative imbalance with effects in Idiopathic Sudden Sensorineural Hearing Loss (ISSHL). Authors conducted a study with 50 patients with ISSHL and 50 healthy participants measuring levels of total oxidant status (TOS), total antioxidant status, paraoxonase and thiol/disulphide in peripheral blood. Furthermore, they calculated a global oxidative stress index. They evaluated the relationship between oxidative markers and severity of HL. Patients woth ISSHL had higher TOS levels than controls and higher oxidative index. There was no significant relation between oxidative markers and severity of HL. Disulphide and TOS showed association with ISSHL according to binary logistic regression model. Findings demonstrated endothelial dysfunction in ISSHL and modifications in oxidants and antioxidants in oxidative stress. Researchers concluded that there is an association between ISSHL with oxidative stress that a decrease in oxygen can damage endothelium by a dysfunction involving inner ear microcirculation.
  • Emerging therapeutic interventions against NIHL (Sha and Schacht, 2017) [USA]: NIHL is one of the principal causes of HL, also notably preventable. It affects quality of life mainly in population between 20 and 69 years old with an important economic cost to society. Authors exposed a review of animal and human models. These studies leaded to therapies now being tested in trials, highlighting the need of further work to improve protective therapies.


Since the theory of free radicals modifying cell cycle emerged it has been used to explain several issues within human illnesses. This theory has been used to propose an explanation of how loud noises impact our hearing. The most relevant characteristic of this idea is that the production of oxidant substrates can cause injury in hair cells, which are unable to regenerate once they are death, either by apoptosis or necrosis pathways. Nevertheless, further research and information is needed to apply this knowledge in useful therapies to prevent NIHL.

Reviews and studies show research and data on the relationship between oxidative stress and NIHL they were conducted in the last five years. All of them were supported by referencing recent resource. Arguments are presented encouraging the idea of an inner ear damage by an imbalance in oxidants and antioxidants production. There was just one experimental study, the rest of them analysed information that was already available on how free radicals can damage the hair cells producing hearing impairment.

In fact, all this scientific observations enforce the theory of a disproportion of oxidant and antioxidant substrates production in vulnerable patients with an important exposure to loud noises to end up showing hearing loss.


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