Noise pollution, water pollution and air pollution are considered to be the three major environmental problems in the world. Sound is caused by the vibration of objects and propagates in a certain medium (such as solid, liquid and gas) in the form of waves. The sound we usually hear is the sound of air. Generally speaking, the frequency of sound waves that the human ear can hear is 20 ~ 20,000,000 Hz, which is called audible sound; Below 20Hz, it is called infrasound; Above 20,000,000 000Hz, it is called ultrasound. The pitch of the sound we hear depends on the frequency of sound waves. High frequency sounds sharp, while low frequency sounds dull. The volume of sound is determined by the strength of the sound. From the physical point of view, noise is a chaotic and irregular combination of sounds with different frequencies and intensities; Music is a harmonious sound.

It is not enough to judge whether a sound belongs to noise only from the perspective of physics, and subjective factors often play a decisive role. For example, beautiful music is music to those who are enjoying it, but it may be noise to those who are studying, resting or concentrating on thinking. Even the same sound, people will have different subjective judgments on the sound in different States and moods, and the sound may become noise or music. Therefore, from the physiological point of view, all sounds that interfere with people's rest, study and work, that is, unnecessary sounds, are collectively called noise. When noise has a bad influence on people and the surrounding environment, noise pollution is formed.

According to the mechanical characteristics of sound source, 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.

The hazards of noise are mainly manifested in: disturbing sleep, damaging hearing, affecting human physiology and the development of children and fetuses.

Experiments show that noise can cause a nervous reaction of human body, stimulate the secretion of renin, thus causing changes in heart rate and hypertension, so some people think that noise in life is an important reason for the deterioration of heart disease and the increase of incidence; Relevant studies have pointed out that noise will reduce the secretion of saliva, gastric juice and gastric acid, and it is easy to suffer from ulcers and duodenal ulcers. In some noisy industrial enterprises, the incidence of ulcers is five times higher than that in a quiet environment. Noise affects people's endocrine function.

In addition, noise can also cause damage to animals and buildings. If the noise is very strong, the bird's feathers will fall off, it will not lay eggs, and it will even bleed internally and eventually die. In 1950s, it was reported that a high-speed plane was flying at a low altitude of 60 meters, and a building on the ground was damaged by noise. ?

Noise sources can be roughly divided into the following categories:

(1) Traffic noise. From various means of transportation, such as cars, trains, planes, etc. With the increase of urban vehicles, urban traffic noise will become more and more serious. At present, the most serious traffic noise in China is honking the horn. ?

(2) factory noise. Factory noise not only directly harms production workers, but also has a great impact on nearby residents. Among the industrial noise, the noise of general electronics industry and light industry is below 90 decibels, the noise of textile mills is between 90 ~ 100 decibels, and the noise of machinery industry is between 8 0 ~ 120 decibels. Industrial noise is the main cause of occupational deafness. ?

(3) Construction noise. During the period of building and road construction, all kinds of construction machinery and transport vehicles produce noise, which causes great interference to the surrounding residents. ?

(4) Social noise. The noise of social activities and family life is also very common, such as the noise of entertainment places, stations, vegetable markets and schools. There are stereos, televisions, etc. At home. ? Noise pollution characteristics

When the sound makes people feel noisy, it is considered as noise pollution. The characteristics of noise pollution are: first, it has a wide influence; Second, unlike water pollution, air pollution and soil pollution, it will not accumulate in the environment. When the sound source stops sounding, the noise pollution disappears immediately.

Prevention and control of noise pollution

1, control noise source

2. Adopt silencing device.

3, the use of sound insulation device

Step 4 Afforestation

The propagation of noise is generally divided into three stages: noise source, propagation path and receiver. The propagation path includes reflection, diffraction and other forms of sound wave propagation. The principle of noise control is to take seven measures such as sound insulation, vibration isolation, sound absorption, muffler, personal protection and building layout before the noise reaches the eardrum. Try to weaken or reduce the vibration of the sound source, or absorb the sound energy in transmission; Or set obstacles to make the sound reflect completely or partially to weaken the effect of noise on the eardrum, so as to achieve the purpose of controlling noise. Discuss and summarize the above points!