noise pollution

noise is the sound produced when the generator is irregular. The sound is caused by the vibration of the object and propagates in a certain medium (such as solid, liquid and gas) in the form of waves. The noise pollution usually refers to man-made. From the physiological point of view, any sound that interferes with people's rest, study and work, that is, unnecessary sound, is collectively called noise. When noise has a bad influence on people and the surrounding environment, noise pollution is formed. Since the industrial revolution, the creation and use of various mechanical equipment have brought prosperity and progress to mankind, but at the same time, it has also produced more and more and stronger noise.

Noise pollution, water pollution, air pollution and solid waste pollution are regarded as four major environmental problems in the world.

classification of noise

according to the mechanical characteristics of sound sources, noise pollution can be divided into: noise caused by gas disturbance, noise caused by solid vibration, noise caused by liquid impact and electromagnetic noise caused by electromagnetic action.

noise can be divided into: <; Low frequency noise of 411Hz, intermediate frequency noise of 411 ~ 1111 Hz and >: 1111Hz high frequency noise.

noise can be divided into steady-state noise, unsteady-state noise, fluctuation noise, intermittent noise and impulse noise.

noise is caused by natural phenomena (see natural noise), and it is also caused by people. Therefore, it is also divided into natural noise and artificial noise.

sources of noise

(1) traffic noise: including noise from motor vehicles, ships, subways, trains and airplanes. Due to the rapid increase in the number of motor vehicles, traffic noise has become the main source of noise in cities.

(2) industrial noise: noise generated by various equipment in the factory. The sound level of industrial noise is generally high, which has a great impact on workers and surrounding residents.

(3) Construction noise: mainly comes from noise emitted by construction machinery. Construction noise is characterized by its high intensity and mostly occurs in densely populated areas, thus seriously affecting residents' rest and life.

(4) Social noise: It includes people's social activities and noise emitted by household appliances and audio equipment. Although the noise level of these devices is not high, they are closely related to people's daily life, which makes people restless during rest, especially annoying and easily causes neighborhood disputes.

(5) Characteristics of noise such as noise pollution in family life

The loudness of sound is related to the "sound pressure"; The sharp or heavy sound is related to the level of "audio"; Whether the sound is pleasant or noisy is related to whether the "tone" is harmonious.

(1) audio audio is the frequency of sound. A vibrating object, the number of vibrations per second is the vibration frequency of the object, and the unit of frequency is hertz. Generally speaking, waves with vibration frequency between 21 Hz and 21111 Hz can be heard by human beings, so they are called sound waves, and the vibration source of sound waves is called sound source. Below 21 Hz and above 21111 Hz belong to infrasound and ultrasound respectively, which can't be heard by human ears.

(2) The sound pressure sound can spread out in the air because the vibrating object causes the local pressure change of the surrounding air through vibration, which causes the local density change of the surrounding air, and the local density change in turn causes the pressure change of the air in the far part. If this continues, the pressure change will be transmitted to the farther part, thus causing the sound to spread. In the process of sound propagation, the pressure change of air pressure relative to atmospheric pressure is called sound pressure, and its unit is Pa. The field of human hearing is quite broad, with an average of about 2×11-5-21 Pa. We can hear the volume of the strongest source, which may be 211,111 times that of the weakest source.

the logarithmic expression of sound overwhelming is used as the expression unit, that is, the sound pressure level is used to express the sound volume. The unit of sound pressure level is decibel. The sound pressure level of the sound we hear in our daily life is about 1-141 decibels. The intensity of noise is also expressed by sound pressure level. The lowest sound level that a normal person's hearing can feel is 1 dB. Whispering softly is about 31 decibels. The conversation language about 1 meters apart is about 61 decibels. It is about 81 decibels in buses. The noise in heavy trucks, weaving workshops and subways is about 111 decibels.

characteristics of noise

noise is a public hazard, so it has the characteristics of public hazard. At the same time, as a kind of sound, it also has acoustic characteristics.

(1) Pollution characteristics of noise

Because noise belongs to sensory pollution, it is different from the pollution caused by other harmful and toxic substances. First of all, it has no pollutants, that is, noise does not leave any toxic substances to the surrounding environment when it propagates in the air; Secondly, the impact of noise on the environment is not accumulated and lasting, and the transmission distance is limited; The noise source is scattered, and once the sound source stops making sound, the noise disappears. Therefore, the noise can't be treated centrally, and it needs to be controlled by special methods.

(2) Acoustic characteristics of noise

Simply put, noise is sound, which has all acoustic characteristics and laws. However, the impact of noise on the environment is related to its strength. The stronger the noise, the greater the impact. The physical quantity to measure the intensity of noise is noise level.

noise control

in order to reduce the impact of noise on the surrounding environment and human beings, the main noise control methods isolate or protect the noise source, the noise propagation path and the receiver, and block or absorb the noise energy. For example, the noise source (motor) is equipped with shock-proof spring or rubber to absorb vibration or cover the whole motor. The path of propagation is generally to block the propagation of noise by using a sound barrier. The protection for the receiver is generally soundproof windows, earplugs and so on.

And governments all over the world usually have corresponding laws or regulations to control excessive noise.

Noise pollution is harmful to people, animals, instruments and buildings, and its degree of harm mainly depends on the frequency, intensity and exposure time of noise. Noise hazards mainly include:

Eight hazards of noise pollution

1. Strong noise can cause ear discomfort, such as tinnitus, earache and hearing loss

According to the measurement, noise exceeding 115 decibels can also cause deafness. According to clinical medical statistics, if you live in a noise environment above 81 decibels, the number of people who are deaf can reach 51%. Medical experts believe that family noise is one of the causes of deafness in children.

2. Reduce work efficiency

Studies have found that noise exceeding 85 decibels will make people feel upset, and people will feel noisy, so they can't concentrate on their work, which will lead to reduced work efficiency.

3. Damage to cardiovascular system

Noise is a risk factor of cardiovascular diseases, which will accelerate heart aging and increase the incidence of myocardial infarction. Medical experts have proved by human and animal experiments that long-term exposure to noise can increase the secretion of adrenal glands in the body, thus raising blood pressure. People who live in noise with an average of 71 decibels for a long time can increase the incidence of myocardial infarction by about 31%, especially at night. The survey found that the rate of myocardial infarction in residents living near expressway increased by about 31%. A survey of 1111 female textile workers showed that the incidence of hypertension was 7.2%, among which the incidence of hypertension was 15.2% for those exposed to 111 dB noise.

4. Noise can also cause nervous system dysfunction, mental disorder, endocrine disorder and even an increase in accident rate

A noisy working environment can cause dizziness, headache, insomnia, dreaminess, general fatigue, memory loss, fear, irritability, inferiority and even insanity. In Japan, there have been cases where people became insane because they could not stand the stimulation of train noise and finally committed suicide.

5. Interference with rest and sleep

Rest and sleep are necessary conditions for people to eliminate fatigue, restore physical strength and maintain health. But noise makes people restless, and it is difficult to rest and fall asleep. When people can't sleep after tossing and turning, they will feel tense, shortness of breath, increased pulse, excited brain, and feel tired or weak limbs the next day. Thus affecting work and study, over time, you will get neurasthenia, which is manifested as insomnia, tinnitus and fatigue.

6. Damage to women's physiological function

Women are threatened by noise, and they may also have irregular menstruation, miscarriage and premature delivery, such as causing female sexual dysfunction, menstrual disorder and increased abortion rate. Experts have conducted a three-year systematic investigation in seven regions, including Harbin, Beijing and Changchun, and found that noise can not only make female workers suffer from noise deafness, but also have adverse effects on their menstruation and fertility. In addition, it can lead to miscarriage, premature delivery and even teratogenesis. Foreign countries have made a survey on the common occurrence of abortion and premature delivery of pregnant women in a certain area, and found that they live around an airport, and the culprit is the huge noise generated by the flying and landing planes.

7. Noise is more harmful to children's physical and mental health

Because children's development is immature, all tissues and organs are very delicate and fragile. No matter the fetus in the body or the newborn child, noise can damage the hearing organs, resulting in hearing loss or loss. According to statistics, there are more than 71 million deaf people in the world today, and a considerable part of them are caused by noise. Expert research has proved that indoor noise is the main cause of children's deafness. If you live with noise above 85 decibels, the deaf can reach 5%.

8. Damage of noise to eyesight

People only know that noise affects hearing, but in fact noise also affects eyesight. The experiment shows that when the noise intensity reaches 91 decibels, the sensitivity of human visual cells decreases and the reaction time of identifying weak light is prolonged. When the noise reaches 95 decibels, 41% people have dilated pupils and blurred vision; When the noise reaches 115 decibels, the adaptation of most people's eyes to light brightness is weakened to varying degrees. Therefore, people who are exposed to noise for a long time are prone to eye fatigue, eye pain, dizziness and tears. At the same time, noise can also make color vision and visual field abnormal. It is found that noise reduces the visual field of red, blue and white by 81%. Therefore, drivers should avoid the noise interference of stereo sound, otherwise it is easy to cause traffic accidents.

Prevention of noise pollution

In order to prevent noise, Professor Ma Dayou, a famous Chinese vocalist, has summarized and studied the hazards and standards of various kinds of noise at home and abroad, and put forward three suggestions:

(1) In order to protect people's hearing and health, the allowable value of noise is 75~91 dB.

(2) ensure conversation and communication, and the allowable value of environmental noise is 45~61 decibels. [1]

(3) It is suggested that the sleep time should be 35~51 decibels.

in buildings, measures taken to reduce noise are mainly

sound insulation and sound absorption. Sound insulation is to isolate the sound source and prevent the noise generated by the sound source from spreading indoors. Planting trees on both sides of the road can play a role in sound insulation for houses on both sides. Sandwich structure made by separating multiple layers of dense materials with porous materials in buildings will also have a good sound insulation effect. In order to eliminate noise, commonly used sound absorption materials are mainly porous sound absorption materials, such as glass wool, mineral wool, expanded perlite, perforated sound absorption board and so on. The sound absorption performance of materials depends on its roughness, flexibility, porosity and other factors.

Chinese psychologists believe that the control of noise environment should take into account not only human factors, but also economic and technical feasibility. Adequate noise control must consider the whole system composed of noise source, sound transmission way and sound receiver. Noise control measures can be aimed at the above three parts or any of them. The contents of noise control include:

(1) To reduce the noise of sound source, industry and transportation industry can choose low-noise production equipment and improve production technology, or change the motion mode of noise source (such as reducing the vibration of solid sound generator by damping and vibration isolation).

(2) reduce the noise in the sound transmission way, control the noise transmission, and change the noise transmission way that has been emitted by the sound source, such as adopting sound absorption, sound insulation, sound barrier, vibration isolation and other measures, and rationally planning the layout of cities and buildings.

(3) When the sound source and transmission route cannot be taken, or the acoustic measures still cannot achieve the expected effect, it is necessary to take protective measures for the sound receiver or the sound receiver. For example, workers who have been exposed to occupational noise for a long time can wear ear protectors such as earplugs, earmuffs or helmets.

although noise control is technically mature now, due to the large scale of modern industry and transportation industry, there are many enterprises and places to adopt noise control. Therefore, we must make a comprehensive balance from the aspects of technology, economy and effect in preventing noise. Of course, specific problems should be analyzed in detail. In places where outdoor, design rooms, workshops or employees work for a long time, the intensity of noise should be low; The warehouse or few people go to the workshop or open place, and the noise is slightly higher. In short, there should be some differences in the treatment of noise at different times, places, properties and durations.

some methods to prevent noise pollution

① the energy of sound in propagation decreases with the increase of distance, so the noise source can be kept away from the place where it needs to be quiet, and the purpose of noise reduction can be achieved. (2) the radiation of sound is generally directional, and the received sound intensity is different when it is at the same distance from the sound source but in different directions. However, when most sound sources radiate noise at low frequencies, the directivity is very poor; As the frequency increases, the directivity increases. Therefore, controlling the propagation direction of noise (including changing the emission direction of sound source) is an effective measure to reduce noise, especially high-frequency noise. ③ Establish sound insulation barriers, or use natural barriers (soil slopes and hills), and use other sound insulation materials and sound insulation structures to block the spread of noise. (4) Using sound-absorbing materials and sound-absorbing structures, the noise acoustic energy in transmission can be converted into heat energy. ⑤ In urban construction, adopt reasonable urban noise prevention planning. In addition, vibration isolation measures are taken to reduce the spread of noise caused by solid vibration.

Utilization and application of noise

Although noise is one of the four major public hazards in the world, it is still useful:

Noise weeding scientists have found that different plants have different sensitivity to different noises. People make noise weed killers. The noise generated by this noise weed killer can make the seeds of weeds germinate in advance, so that weeds can be removed with drugs before crop growth, and the smooth growth of crops can be ensured by the clever strategy of "playing hard to get".

It is well known that noise can diagnose diseases, and beautiful music can cure diseases. But how can noise be used for diagnosis? Recently, scientists have made a laser hearing diagnosis device, which consists of a light source, a noise generator and a computer tester. When in use, the micro-noise generator first generates weak and short noise to vibrate the eardrum, and then the microcomputer will display the data of the eardrum function according to the echo for the doctor to diagnose. It has the advantages of rapid test, no damage to the eardrum and no pain, and is especially suitable for children. In addition, noise thermometry can also be used to detect human lesions. The three noise reduction measures commonly used in active noise reduction, that is, noise reduction at the sound source, noise reduction during propagation and noise reduction at the human ear, are all passive. In order to actively eliminate noise, people invented the technology of "active noise elimination". Its principle is that all sounds are composed of a certain frequency spectrum. If a sound can be found, its frequency spectrum is complete with the noise to be eliminated.