| Although its presence lingered unaddressed | | | | public health and welfare; to set noise |
| for many years, environmental noise is now | | | | emission standards for major sources of noise |
| recognized as a significant health issue. | | | | in the environment, including transportation |
| Environmental or ambient noise is unwanted or | | | | equipment and facilities, construction |
| harmful outdoor sound created by human | | | | equipment, and electrical machinery; and to |
| activities, including noise emitted by means | | | | recommend regulations for controlling |
| of transport - road traffic, rail traffic, | | | | aircraft noise and sonic booms. Also in the |
| air traffic - and from sites of industrial | | | | 1970s, the Occupational Safety and Health |
| activity. From delivery trucks to air | | | | Administration began to try to reduce |
| conditioners, we are constantly bombarded by | | | | workplace noise. And over the past 30 years, |
| sounds that go unnoticed for the most part. | | | | the general public has become increasingly |
| However, out-of-earshot should not mean | | | | aware of the hazards of environmental noise, |
| out-of-mind. It is precisely these innocuous | | | | and its ability to combat it on an individual |
| environmental noises that should be sounding | | | | and collective level.One of the most |
| an alarm.Those involved with the more obvious | | | | effective environmental noise abatement |
| noise sources such as airports, shooting | | | | technologies to be developed is the noise |
| sports, manufacturing or even musical | | | | barrier wall, or sound wall. Sound walls are |
| concerts have long known the detrimental | | | | classified as reflective or absorptive. Hard |
| effect of extreme noise levels on long-term | | | | surfaces such as masonry or concrete are |
| hearing. Only recently, however, has | | | | considered to be reflective. This means most |
| environmental noise been thoroughly | | | | of the noise is reflected back towards the |
| researched for its affect on our mental and | | | | noise source and beyond. A barrier wall such |
| physical health - and the findings may | | | | as the Sound Fighter(R) LSE 2000 with a |
| surprise you. But to gain a better | | | | porous surface material and sound-dampening |
| understanding, one needs a basic education on | | | | content material is said to be absorptive. |
| what, exactly, noise is.Noise intensity is | | | | This means little or no noise is reflected |
| measured in decibel units. The decibel scale | | | | back towards the source or elsewhere.Sound |
| is logarithmic; each 10-decibel increase | | | | walls are performance rated in two |
| represents a tenfold increase in noise | | | | categories: Sound Transmission Class (STC) |
| intensity. Human perception of loudness also | | | | and Noise Reduction Coefficient (NRC). The |
| conforms to a logarithmic scale; a 10-decibel | | | | STC determines the amount of noise energy |
| increase is perceived as roughly a doubling | | | | transmitted through the wall material. The |
| of loudness. Thus, 30 decibels is 10 times | | | | NRC determines the amount of energy absorbed |
| more intense than 20 decibels and sounds | | | | by the wall material and the amount of energy |
| twice as loud; 40 decibels is 100 times more | | | | reflected back towards the source.Walls |
| intense than 20 and sounds 4 times as loud; | | | | having STC ratings of 30 or more means that |
| 80 decibels is 1 million times more intense | | | | less than 0.1 percent of the noise energy is |
| than 20 and sounds 64 times as loud. Distance | | | | transmitted through the barrier material. |
| diminishes the effective decibel level | | | | Many State Department of Transportation |
| reaching the ear. Thus, moderate auto traffic | | | | specifications require minimum STC ratings of |
| at a distance of 100 ft (30 m) rates about 50 | | | | 24.NRC measures the amount of sound energy |
| decibels. To a driver with a car window open | | | | absorbed and measures the amount of sound |
| or a pedestrian on the sidewalk, the same | | | | energy reflected back towards the source. NRC |
| traffic rates about 70 decibels; that is, it | | | | ratings will range between 0 (100% |
| sounds 4 times louder. At a distance of 2,000 | | | | reflective) to 1 (100% absorptive). A wall |
| ft (600 m), the noise of a jet takeoff | | | | with an NRC rating of .85 means the wall |
| reaches about 110 decibels-approximately the | | | | absorbs 85% of the noise and reflects 15% of |
| same as an automobile horn only 3 ft (1 m) | | | | the noise back towards the source. NRC |
| away. ¹Subjected to 45 decibels of noise, | | | | ratings equal to or greater than .85 are |
| the average person cannot sleep. At 120 | | | | considered to be good sound absorbers and are |
| decibels the ear registers pain, but hearing | | | | often used as the minimum requirement when |
| damage begins at a much lower level, about 85 | | | | considering absorptive walls.A good sound |
| decibels. The duration of the exposure is | | | | wall is a sound-absorbing wall with a STC |
| also important. There is evidence that among | | | | rating of 30 or more and a minimum NRC rating |
| young Americans hearing sensitivity is | | | | of .8.Is a sound wall the best mitigation |
| decreasing year by year because of exposure | | | | option for every application? Certainly not. |
| to noise, including excessively amplified | | | | There are effective mitigation tools for any |
| music. Apart from hearing loss, such noise | | | | situation - from earplugs to ceiling tiles. |
| can cause lack of sleep, irritability, | | | | But for many outdoor applications such as |
| heartburn, indigestion, ulcers, high blood | | | | traffic, manufacturing, compressor and |
| pressure, and possibly heart disease. One | | | | commercial retail noise, nothing outperforms |
| burst of noise, as from a passing truck, is | | | | a well-engineered and efficient absorptive |
| known to alter endocrine, neurological, and | | | | sound wall.* * *¹ Infoplease, |
| cardiovascular functions in many individuals; | | | | Copyright © 2000-2006 Pearson Education, |
| prolonged or frequent exposure to such noise | | | | publishing as Infoplease.² H.I.N.S., |
| tends to make the physiological disturbances | | | | IncMurray Stacy is Vice President of Sound |
| chronic. In addition, noise-induced stress | | | | Fighter Systems, LLC, which has been |
| creates severe tension in daily living and | | | | researching, designing and manufacturing |
| contributes to mental illness.¹Does this | | | | highly efficient absorptive noise barrier |
| mean we are doomed to a noise-filled life of | | | | walls since 1973, making it the oldest |
| stress? Fortunately, no. Noise is now | | | | established manufacturer of such products in |
| recognized as a controllable problem that can | | | | America. Sound Fighter walls have been |
| be minimized via varied abatement | | | | produced for unique noise mitigation |
| technologies. In the United States the Noise | | | | applications around the world, and several of |
| Control Act of 1972 empowered the | | | | the company's walls are in their 30th year of |
| Environmental Protection Agency to determine | | | | effective service. |
| the limits of noise required to protect | | | | |