For a long time, the noise and vibration laboratory has carried out a lot of experiments on Taos Hum and low-frequency noise in order to determine the harm and impact of different noises on human beings. Normally, what we call low-frequency noise is sound waves with frequencies below 200Hz. Among them, the frequency range with obvious influence on human body is 3-50hz. Sound waves below 20Hz are called infrasound. Infrasound widely exists in our life, usually infrasound will not bring harm to our life, but a certain intensity of infrasound is more destructive. The frequency of infrasound is similar to the natural frequency of human organs. For example, the natural frequency of human organs is 3 ~ 17Hz, the natural frequency of head is 8 ~ 12Hz, and the natural frequency of abdominal viscera is 4 ~ 6Hz. When more than a certain intensity of infrasound on the human body, will make people dizzy, nausea, vomiting, loss of balance, mental depression, loss of consciousness, or even internal blood vessels burst and die.
In addition to the high pressure level infrasound below 20Hz has great harm to human body, the low frequency noise of high pressure level is also extremely harmful. The most common is broadband noise at 100Hz and below. Although the low-frequency noise directly affect on human physiology is not high frequency noise is apparent, but will have far-reaching influence on human health, lead to blood sugar, blood fat of triglyceride and cholesterol levels, bring damage to the auditory organs, to hearing loss or loss of, or will affect the development of the fetus’s nervous system, causing abortion or fetal death, etc.
Normally, our human ears can pick up sounds in the range of 20Hz to 200Hz. As we get older, our ears become less sensitive, and we lose track of some frequencies. However, certain middle-aged and elderly people can still hear a lower frequency, so the above mentioned 2% of the population can hear the low-frequency Hum. Moreover, in the suburbs of the wilderness, low-frequency noise has no interference absorption of urban high-rise buildings and spreads more smoothly. After nightfall, when many of the high-frequency noise sources disappear during the day, the low-frequency Hum becomes more pronounced, which is why suburban residents are more likely to hear a Hum on a quiet night. These features are identical to Taos Hum and the other hum around the world. Moreover, low-frequency noise is accompanied by infrasound, and when the energy exceeds a certain level, headache, anxiety, insomnia and nervous breakdown as described by many of the victims above may occur.
How to prevent low frequency noise?
Low frequency noise control is one of the recognized problems in the field of noise control. Why is low-frequency noise prevention difficult? Low frequency noise, unlike high frequency noise, is often ignored. Low-frequency noise has a low frequency, and its vibration frequency is small when propagating in the air. Energy decays slowly with the propagation of distance, so the propagation distance is long and the harm range is wide. Moreover, the wavelength of low-frequency noise is longer, 7000Hz sound wave can be blocked with a piece of paper, while 7Hz infrasound can penetrate reinforced concrete with a thickness of more than ten meters, which can be easily traversed when low-frequency noise encounters obstacles, so the prevention difficulty coefficient is more than that of high-frequency noise.
However, this is not the worst thing. Although with the improvement of living standards, people do pay more and more attention to environmental noise. However, the current environmental noise standards have not targeted at low-frequency noise. That is to say, when a resident complained about the low-frequency noise of the central air conditioner upstairs, and the department concerned used professional detection equipment to test, the result showed that the decibel number of the noise is not high, so according to the national standard is not illegal, even if the low-frequency noise seriously interfered with the victim’s normal life. Can the victim only suffer from low-frequency noise in silence?
Although it will take some time for the government to develop relevant standards and the development of relevant low-frequency noise research, acoustical experts have given us many effective Suggestions on “protecting the transmitter and cutting off the transmission path of noise” as follows:
(1) Pay attention to the harm of low-frequency noise. If the above “Hum” phenomenon occurs, do not ignore it.
(2) If it is determined that the low-frequency noise is caused by remote factory noise or geological tectonic activity in nature and such low-frequency noise is often transmitted through air, the use of multi-layer and double-layer vacuum glass Windows can play a certain role in sound insulation.
(3) If it is judged that the low-frequency noise is caused by the low-speed operation of the water pump on the top floor and the low-frequency operation of the variable frequency air conditioner, it is indeed difficult to prevent the noise transmitted through the wall. When faced with such a situation, softer furniture materials can be used, such as the use of flexible, fluffy materials for wall decoration, while thicker curtains and softer materials of the bed and sofa can effectively alleviate the effects of low frequency noise. . Because the furniture of these materials is a good sound absorbing material, it can play a buffering role to some extent.
(4) It is recommended that you turn on an electric fan, an air purifier, or play a soothing music, etc. Depending on the human auditory masking effect, these volumes are loud enough for the human ear to ignore the deep hum.