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NOISE MITIGATION

Noise pollution is an inescapable fact of life. Not only are decibel levels increasing, but they are also expanding their reach. Estimates are that 180,000 persons move into urban populations centers each day. As they do, noise pollution is pushed farther into previously, quieter rural regions.

Noise Mitigation Goals

Not all noise is bad. A baby’s laugh, a favorite piece of music, birds chirping, ocean waves breaking gently along the shore—These are sounds most would accept as desirable and pleasant. They improve the quality of life, and in some cases, they may even be therapeutic. Noise pollution does more than disrupt our quiet hours. It detracts from the pleasure and benefits we derive from the desirable sounds in our lives. Today, there is hardly a place on the globe where man-made noise pollution does not intrude, disrupting ecosystems and degrading the quality of life. The goal of noise mitigation is to target and reduce this unwanted, harmful noise.

Noise Mitigation Methods

Noise pollution often invades an environment from multiple sources. Street traffic, aircraft passing overhead, industrial and construction machinery, the noise generated by other people and a myriad of other sources can create undesirable sound levels.

 

At the turn of the twentieth century, vehicle traffic noise affected only 20 to 25 percent of the land area in the continental United States and was confined mainly to large urban centers. Today, more than 97 percent of the country is exposed to vehicle generated noise pollution. The pervasive nature of noise pollution requires mitigation efforts that involve one or a combination of the following methods:

 

Mitigating Noise at Its Source

Eliminating or reducing noise at its source is the first mitigation priority. Controlling source noise reduces the need for secondary noise attenuation and lowers the overall expense of mitigation efforts farther from the source.

Transmission Path Mitigation

Once noise is generated and moving through a transmission medium such as the air, water, walls, or floors of a building, noise mitigation focuses on preventing or reducing the intensity of the sound that reaches the person(s) receiving the noise. The typical techniques for mitigating sound along its transmission path include:
 

Blocking: Placing mass barriers made of high-density sound reflective materials between the receiver and noise source

Absorption: Using materials with a porous exterior that allows sound waves to penetrate to the interior where they are absorbed and dissipated

 

Isolating vibrations: Sound levels are reduced by isolating, absorbing, or redirecting vibrations from heavy machinery and other noise sources

 

Receiver Protection

Protection is the mitigation method closest to the person receiving the noise. It may take the form of personal hearing protection but can also include structural and design components around the receiver’s personal space.

Common Noise Mitigation Applications

Comprehensive noise mitigation programs generally combine multiple mitigation methods, reducing noise levels at the source, along the transmission path, and – where necessary – providing protection at the receiver end.

Industrial and Construction Applications

 

Source mitigation

Properly maintained equipment produces less noise. Selecting equipment with quiet technology features such as electric motors instead of internal combustion engines, anti-vibration shock absorbers, and advanced muffler and exhaust systems can reduce source noise.

 

Transmission path mitigation

Acoustic and mass barriers can be used to isolate and contain the noise produced by machinery and heavy equipment, reducing the decibels reaching surrounding areas.

 

Receiver protection

Hearing protection and workspaces enclosed by acoustic barriers protect workers from harmful noise levels

 

Vehicle Traffic Applications

 

Source mitigation

Regulations requiring quieter engine operation and proper vehicle maintenance can reduce traffic noise sources. Prohibiting the use of truck engine and air brakes in residential districts is a common method of controlling vehicle noise at its source. The use of noise abatement procedures around airports, where engines must be throttled back while passing over residential or noise sensitive areas is a common source control effort.

 

Transmission path mitigation

Noise attenuating acoustic barriers, properly designed and placed along highways have been shown to reduce local noise levels. Increasingly, planners are also using landscaping as a way to block and redirect noise from traffic and other sources.

 

Residential

 

Source mitigation  

Opting for quiet technology appliances is a way for homeowners to reduce noise pollution within the structure. Selecting electric tools over gas operated ones can also reduce noise levels when performing yard and garden chores.

 

Transmission path mitigation

Home construction materials and insulation available today provide increased sound blocking and absorption capabilities. Functional landscaping can also be used to block and reduce the noise reaching the structure from external sources.

 

Receiver protection

House designs can position sound sensitive areas, like bedrooms, home offices and dens away from exterior noise-producing sources.

Adaptive Noise Mitigation

While every noise control applications may be unique, the environments surrounding them evolve over time. Traffic patterns change. New highways are built. New construction projects begin. Local business operations change. Effective noise mitigation plans should meet current noise control requirements while retaining the flexibility to adapt to future changes in the surrounding noise environment.

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