The principle is sound-absorbing materials What » Night of the land of snow is very quiet »
In the classroom, meeting room or music room, we often see the back wall is equipped with sound-absorbing panels to you to sound, so as to avoid interference by outside people. Sound-absorbing panels on the surface there are many holes, sound into the hole, it will in the next structure somewhat like a sponge in the wall reflection indiscriminately, until most of the acoustic energy is consumed, turned into heat, to the effect of noise.
    Snow when the ground, buildings and trees often covered with a layer of snow. And the different ice, snow is not hard solids, contrary to polymerization with sparse snowflakes, which includes many small gaps, a bit like sound-absorbing panels in the structure. These gaps on a sound-absorbing acoustic effects, especially on frequencies higher than 600 H2 acoustic effect is very significant. The snow land of unusual quiet night, is this reason.

Noise hazards to human
The impact of noise on hearing: 80 dB in the long-term living environment of more than 50 percent of deafness, often wearing headphones to listen to the concert lead to permanent hearing loss.
The impact of noise on the visual: often in a noisy environment, reduce the sensitivity of people eyes, dilated pupils, scattered large, color and vision abnormalities, produce confusion, vision problems, slow response to the phenomenon would lead to the occurrence of traffic accidents.
The impact of noise on the digestive system: noise make saliva, decreased secretion of gastric juices, causing sluggish appetite caused by gastrointestinal diseases.
Noise on the growth and development of children: in the noisy environment of intellectual development of children living quiet environment than in the low 20 percent nutritionist found that the noise so that the body of vitamin B1, B2, B6, amino acid, glutamic acid, lysine, etc. Nutrient consumption increased, the growth and development of children affected greatly.
Noise on the cardiovascular effects: noise will make the regulatory function of a brain phenomenon out of control, causing breathing speed up, fierce beating heart, high blood pressure, vasospasm, hypertension, and so trigger cardiovascular and cerebrovascular diseases.
Noise on the impact of the immune system: a long period of noise to the immune system dysfunction, people vulnerable to infection pathogenic microbes and trigger skin or other diseases and even cancer.
The impact of noise on sleep: the noise impact on sleep quality and quantity. Speed up the continuous noise of deep sleep to light sleep rotating, so that shortened sleeping time. The sudden noise at 40 dB, so that 10 percent of the people woke up; 60 dB at 70 per cent of people woke up. Sleep will not seriously affect people's health and work.
Noise Control
As extremely harmful to human noise, the noise of people through in-depth study and sum up a lot of noise control methods, summarized as follows:
Noise Control Method 1: Active noise reduction. Active noise reduction is the use of computer technology, according to the noise frequency, amplitude, period, and other characteristics of sampling, and generate close to the RP-sync signals superimposed to noise control purposes. At present, the kind of noise control methods is not enough maturity, in the development stage.
Noise Control Method 2: passive noise reduction. Most of noise reduction methods are passive noise reduction. In accordance with the use of materials and parts can be divided into vibration noise control, sound-absorbing noise control noise and noise control. In most cases, are usually several ways of use. According to the present material technology and construction technology, any noise can be the basic governance.