“Can you hear me now?” Noise 101, A Primer to Noise Analysis

Noise impact analysis for environmental planning documents can be one of the more daunting resources to tackle. How noise is produced and who or what is affected is very complex. In fact, even the definition of noise can be controversial. Most define noise as unwanted sounds.  But consider this: some hear opera as distinctly unpleasant,  and others embrace the ear-splitting roar of fighter jets as the highly emblematic sound of freedom.  Ultimately, it all lies in the ears of the beholder. The complexity arises because there could be multiple sources, receptors, and metrics used to describe noise.

A proposed project requiring an environmental review can have a number of noise-making activities associated with the action, from construction noise to operational noise, as well as the spawned traffic noise. At some time during our lives we all have been exposed to the familiar cacophony of construction.  Whether it’s the scraping of dirt, rocks, and asphalt by graders and pavers, the pounding of a pile driver, or the rapid hammering of a jackhammer, we recognize them easily.

But just when we think all that construction is over and done with, then operational noise predominates.  This can be in the form of the roar of a military jet, the hum of vehicular traffic, “kabooms” from range and training exercises, the churning of power from generators and HVAC systems, or the noise of a renewable energy wind turbine. The list can be endless, and this is just the proposed noises; the existing ambient conditions may have some of the same noises or different sources altogether.

After identifying all the sources of the existing noise and proposed noise, we then determine who and what can be affected, and how. The “who” can be both human and wildlife, with humans having the more diverse set of potential impacts.  For example, very loud prolonged noises can produce hearing loss, moderate noise is often a cause of annoyance and stress.  And intermittent events that interfere with speech communication can have a detrimental effect on classroom learning for children. Loud impulse noises like the crack of a gunshot or the passing of a low-level military jet create a startle effect. Health effects have been purported by the constant low frequency hum of a large wind turbine. Wildlife is also affected.   Startled nesting birds may flee their nests, exposing eggs and young to weather or opportunistic predators, and loud noises can alter breeding habits of many species.  Underwater sound can interfere with whales and marine mammals’ internal navigation. The “what” can include buildings and cultural sites that when exposed to continued vibration from loud noise can suffer damage, visible, and sometimes invisible.

Now that the noise sources and receptors are selected, it really starts getting complicated. First, the appropriate noise metrics need to be identified and applied. Noise metrics come in many flavors: A-weighting, C-weighting, Peak Noise, Sound Exposure Level, Day-night Average Sound Level, Equivalent Sound Level, are just a few metrics that are used, and one or more may apply depending upon the situation. Except for the most rudimentary evaluations, or for situations where a model has not been developed, most noise analysts use computer models to predict noise levels. Please excuse the alphabet soup but some of the computer models include: Road Construction Noise Model, Traffic Noise Model, Noisemap, MRNMap, SARNAM, BNoise2, AAM, AEDT, INM, SoundPLAN, and CadnaA, and each have their own specific use. For example, military aircraft noise is calculated using Noisemap, where civilian aircraft is best modeled with AEDT.

Noise is a complex topic and to properly address it in an environmental planning document requires knowledge of many aspects of the noise environment. If you have a noise challenge with your project, Scout Environmental is available with solutions to help guide you through the process.

Contact hello@scoutenv.com for further questions.