What’s With All the Noise?
Understanding the Importance of Sound Monitoring and Compliance
John Weber, P.E.
Manager Civil Engineering and Environmental Compliance Group, GAI Consultants, Inc.
As industries continue to grow and transportation infrastructure expands across the U.S., we have seen an increase in the number of sound monitoring studies requested by our clients, local governments, and individuals.
Many municipalities and counties have ordinances regulating permissible sound levels in connection with specific activities and within specific zones. Often these ordinances are called “noise ordinances.” However what is actually measured is not “noise” but “sound,” specifically Sound Pressure Levels (SPLs).
Why We Don’t Measure “Noise”
We measure sound because sound is an objective means to measure the surrounding environment. “Noise,” on the other hand, is subjective. What is “noise” to one person may not be considered “noise” to someone else. A heavy metal concert can be reported as “music” to one person’s ears and defined as “noise” to someone else. A normal conversation between two people on a street corner may go unnoticed. But the same conversation in the local library could be construed as “noise” by its patrons.
According to the EPA, the traditional definition of noise is “unwanted or disturbing sound,”… “The air around us is constantly filled with sounds, yet most of us would probably not say we are surrounded by noise. Though for some, the persistent and escalating sources of sound can often be considered an annoyance. This “annoyance” can have major consequences, primarily to one’s overall health.”
What is and what is not “noise” is in the eye, or ear, of the beholder. Thus it is important to have a non-subjective means to determine what is actually going on in the environment.
Understanding Sound Levels
Sound levels are measured in a unit known as decibels (dB). Decibels are a logarithmic scale interpretation of Sound Pressure Levels, which means that each time a decibel level increases by 10, the intensity doubles. Therefore 50 decibels is twice as “loud” as 40 decibels.
Sound pressure levels continuously over 90 dB can cause hearing loss. Levels over 130, even for a short period of time, cause immediate damage to the ear.
As can be seen from the chart above, if a resident (sensitive receptor) usually experiences only 50 dB on their property or in their existing environment and is suddenly exposed to 70 dB from a new interstate or industrial site, a significant increase has occurred.
However, measuring sound levels and getting accurate data is not a simple task. There are all sorts of ways to measure a sound environment. Some don’t yield any useful data. And others give results that are confusing at best. Also, many factors need to be considered including requirements of local ordinances or federal requirements (e.g. FERC), as well as when to use statistical levels to represent values not easily gathered.
Overall, it is important to think about the impact of sound on our environment and follow established noise ordinances and other regulatory requirements before, during, and after activities or projects that may increase existing levels. Construction or development projects especially benefit from sound monitoring studies by a qualified consulting firm to ensure project activities comply with sound level regulations. “Peace and quiet” is becoming more and more elusive in our busy world, so any opportunity to “keep the noise down” is something to be considered.
U.S. Environmental Protection Agency. (n.d.). Noise Pollution. Retrieved from http://www3.epa.gov/air/noise.html.