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Be on Guard: Low Frequency Noise is Chronically Damaging Your Health

Author:   Date:2018-07-03  From:  Hits:22

Low frequency noise is full of modern life

As early as in the early 1990s, low frequency noise has quietly begun to affect people's lives. At that time, some "karaoke halls" and "discos" in the residential areas were booming. Though there are the thick walls and soundproofing equipment in those entertainment venues, they block only the high frequency songs. Low frequency noise such as the drum sound in the dance hall can pass through the wall, direct access to the living room, bedroom of the citizens. In addition, with the completion of urban roads, bridges and various buildings, especially in some residential areas, the elevators and the transformers and pumps that were originally placed outside the building were moved into the residential buildings(This way of using high-pressure water pump to supply water will produce strong vibration and low-frequency noise), the vibration generated during use forms low frequency noise. There are four main types of low frequency noise sources: elevator, transformer, central air conditioner (including cooling towers) and traffic noise.

Acoustic characteristics of low frequency noise

Low frequency noise is different from high frequency noise. High frequency noise can decay quickly with distance or encounter obstacles. For example, high frequency noise point source declines 6db per 10 meters. While the low frequency noise is decremented very slowly, long sound waves, can easily pass through obstacles, which can strikes long distance and penetrates the wall straight into the human ear. Vibration, low frequency noise and general noise all have a common property, that is they are all vibration waves, a way of energy transmission.

Low frequency noise transmission channel

Low-frequency noise is mainly divided into structural sound transmission, air sound transmission and standing wave according to the way for spreading. Structure sound refers to the transformer, water pump and central air conditioner installed in the building transmit the low-frequency vibration sound waves to various households through the structural girders and load-bearing beams of the residential building. Air transmission means that low frequency noise is transmitted directly to the residential area through the air. Standing wave means that low frequency noise forms multiple standing waves during the transmission process. Low frequency noise has the strongest amplitude in the antinode, which is most harmful to human health. The direct effect of low frequency noise on physiology is not as obvious as high frequency noise. But recently experts in low frequency noise research in China pointed out low frequency noise can cause neurosis such as headaches and insomnia.

Low frequency noise is not easy to attenuate

Low frequency noise is not as harsh as emergency brakes and disco music, but both will produce sound pressure. High frequency noise can decay rapidly as the distance is further away or encounters obstacles. Point source of high frequency noise decreases 6 db per 10 meters, the linear sound source on the road can also drop 3 decibels per 10 meters. However, the low frequency noise is decremented very slowly. Therefore, it is possible to strike long distances and penetrate the wall and straight into the human ear.

Low frequency noise causes chronic damage

Experts say that noise pollution is already the top of the world’s seven major public nuisances. And low frequency noise is a chronic injury to the human body, which can not be ignored.

In the past, low frequency sounds were considered not harmful to human hearing. But recent research has found even low frequency sounds of less than 2 minutes (90 seconds) will also have a significant impact on the hearing organs, low frequency or even infrasound may cause damage to human hearing. If it does, then the low-frequency sound of the open windows and wind turbines on the highway may be one of the factors that are harmful to hearing.

Because low frequency noise can be direct access to human ear bones, and it will make people's sympathetic nervous, elevate blood pressure and endocrine disorders. People who are forced to accept this noise are easy to worry, excited, irritable, and even losing intellect. If you are exposed to low frequency noise for a long time, it is easy to cause neurasthenia, insomnia, headache and other neurosis, even affecting the fetus in the belly of pregnant women. It is quite incorrect for many people to hold a tolerant attitude.

Humans can only hear sound waves of 20-20000 Hz, and narrowed as the age increases. Prolonged exposure to sonic noise can cause hearing loss. The effect on frequencies below 250 Hz is more difficult to determine. Effects below 20 Hz are not heard by the human ear. Effects below 20 Hz are not heard by the human ear, it is also often unaware that this low-frequency "noise" can also cause damage to hearing.

Research by Markus Drexx, a neuroscientist at Maximilian University in Ludwig, Germany found that 21 normal hearing volunteers exposed to 30 Hz sound in the soundproof enclosure for 90 seconds, this noise is similar to the sound of opening a window on a highway. Then the hearing of these volunteers was tested with spontaneous otoacoustic emissions (SOAE). Otoacoustic emission is a kind of audio energy produced in the cochlea, released into the external auditory canal by ossicular chain and tympanic membrane conduction. Otoacoustic emission originates from the cochlea in the form of mechanical vibration, it is now widely accepted that these vibrational energies are derived from the active movement of outer hair cells. This movement of outer hair cells can be spontaneous, can also be a response to external stimuli. Its motion causes mechanical vibration of the basement membrane through mechanical contact with its adjacent structure in the Corti, this vibration is transmitted in the form of pressure changes in the lymph of the inner ear, and push the ossicular chain and tympanic membrane vibration through the oval window, eventually causes air vibration in the external auditory canal. Because the frequency of this vibration is hundreds to thousands of hertz, belongs to audio frequency range (20-20000Hz), so it is called otoacoustic emission. As the name suggests, it is the sound made by the ear. In fact, it is only the reverse process of the audio energy generated in the cochlea through the middle ear to the external auditory canal, and then released in the form of air vibration. Spontaneous otoacoustic emissions have become a tool for diagnosing hearing loss.

In general, spontaneous otoacoustic emissions are relatively stable. However, spontaneous otoacoustic emissions of volunteers exposed to low-frequency sounds for 90 seconds showed strong and weak shocks. This fluctuation lasts for about 3 minutes. This change does not mean hearing impairment, but it means damage-sensitive state. The results of this study suggests that if exposed to low frequency noise sound environment for a long time, hearing may cause persistent damage. The study was published in the Royal Society of Open Science.

M. Charles Liberman, an ear scientist at Harvard Medical School, emphasized this study explains that many people may have been exposed to a silent environment, and their hearing are seriously threatened. To further explore the harm caused by this low frequency noise pollution, more repetitive research should be done. In addition, you should simulate common low-frequency sounds or noises such as wind turbines, to study the possible harm of these sounds to human hearing.

Low frequency noise – prevention

Experts said that low-frequency noise is mainly divided into structural sound transmission, air transmission and standing wave according to the propagation route, and the standing wave is the most harmful. For structural sound transmission caused by transformers, pumps in the building, vibration reduction measures can be added when installing elevators, transformers, pumps, etc. It is best to install these devices outside the building. For air transmission, ventilation sound insulation windows can be installed on the windows of the house to improve.


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