Although its presence lingered unaddressed for many years, environmental noise is now recognized as a significant health issue. Environmental or ambient noise is unwanted or harmful outdoor sound created by human activities, including noise emitted by means of transport - road traffic, rail traffic, air traffic - and from sites of industrial activity. From delivery trucks to air conditioners, we are constantly bombarded by sounds that go unnoticed for the most part. However, out-of-earshot should not mean out-of-mind. It is precisely these innocuous environmental noises that should be sounding an alarm.

Those involved with the more obvious noise sources such as airports, shooting sports, manufacturing or even musical concerts have long known the detrimental effect of extreme noise levels on long-term hearing. Only recently, however, has environmental noise been thoroughly researched for its affect on our mental and physical health - and the findings may surprise you. But to gain a better understanding, one needs a basic education on what, exactly, noise is.

Noise intensity is measured in decibel units. The decibel scale is logarithmic; each 10-decibel increase represents a tenfold increase in noise intensity. Human perception of loudness also conforms to a logarithmic scale; a 10-decibel increase is perceived as roughly a doubling of loudness. Thus, 30 decibels is 10 times more intense than 20 decibels and sounds twice as loud; 40 decibels is 100 times more intense than 20 and sounds 4 times as loud; 80 decibels is 1 million times more intense than 20 and sounds 64 times as loud. Distance diminishes the effective decibel level reaching the ear. Thus, moderate auto traffic at a distance of 100 ft (30 m) rates about 50 decibels. To a driver with a car window open or a pedestrian on the sidewalk, the same traffic rates about 70 decibels; that is, it sounds 4 times louder. At a distance of 2,000 ft (600 m), the noise of a jet takeoff reaches about 110 decibels"approximately the same as an automobile horn only 3 ft (1 m) away.

Subjected to 45 decibels of noise, the average person cannot sleep. At 120 decibels the ear registers pain, but hearing damage begins at a much lower level, about 85 decibels. The duration of the exposure is also important. There is evidence that among young Americans hearing sensitivity is decreasing year by year because of exposure to noise, including excessively amplified music. Apart from hearing loss, such noise can cause lack of sleep, irritability, heartburn, indigestion, ulcers, high blood pressure, and possibly heart disease. One burst of noise, as from a passing truck, is known to alter endocrine, neurological, and cardiovascular functions in many individuals; prolonged or frequent exposure to such noise tends to make the physiological disturbances chronic. In addition, noise-induced stress creates severe tension in daily living and contributes to mental illness.

Does this mean we are doomed to a noise-filled life of stress? Fortunately, no. Noise is now recognized as a controllable problem that can be minimized via varied abatement technologies. In the United States the Noise Control Act of 1972 empowered the Environmental Protection Agency to determine the limits of noise required to protect public health and welfare; to set noise emission standards for major sources of noise in the environment, including transportation equipment and facilities, construction equipment, and electrical machinery; and to recommend regulations for controlling aircraft noise and sonic booms. Also in the 1970s, the Occupational Safety and Health Administration began to try to reduce workplace noise. And over the past 30 years, the general public has become increasingly aware of the hazards of environmental noise, and its ability to combat it on an individual and collective level.

One of the most effective environmental noise abatement technologies to be developed is the noise barrier wall, or sound wall. Sound walls are classified as reflective or absorptive. Hard surfaces such as masonry or concrete are considered to be reflective. This means most of the noise is reflected back towards the noise source and beyond. A barrier wall such as the Sound Fighter LSE 2000 with a porous surface material and sound-dampening content material is said to be absorptive. This means little or no noise is reflected back towards the source or elsewhere.

Sound walls are performance rated in two categories: Sound Transmission Class (STC) and Noise Reduction Coefficient (NRC). The STC determines the amount of noise energy transmitted through the wall material. The NRC determines the amount of energy absorbed by the wall material and the amount of energy reflected back towards the source.

Walls having STC ratings of 30 or more means that less than 0.1 percent of the noise energy is transmitted through the barrier material. Many State Department of Transportation specifications require minimum STC ratings of 24.

NRC measures the amount of sound energy absorbed and measures the amount of sound energy reflected back towards the source. NRC ratings will range between 0 (100% reflective) to 1 (100% absorptive). A wall with an NRC rating of .85 means the wall absorbs 85% of the noise and reflects 15% of the noise back towards the source. NRC ratings equal to or greater than .85 are considered to be good sound absorbers and are often used as the minimum requirement when considering absorptive walls.

A good sound wall is a sound-absorbing wall with a STC rating of 30 or more and a minimum NRC rating of .8.

Is a sound wall the best mitigation option for every application? Certainly not. There are effective mitigation tools for any situation - from earplugs to ceiling tiles. But for many outdoor applications such as traffic, manufacturing, compressor and commercial retail noise, nothing outperforms a well-engineered and efficient absorptive sound wall.

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