Nearly everyone has a story about annoying noises—the roommate who plays music at all hours of the night, the would-be dragsters on the freeway nearby, or the airplanes roaring past overhead. Obnoxious sounds can distract us and disrupt the normal balance of our lives. In severe cases, noise can contribute to increased aggression, hypertension, and stress. Long term effects of high levels of noise exposure include hearing loss, tinnitus (ringing in the ears), sleep disturbance, and increased blood pressure. It might also disrupt the hearing of wildlife, negatively impacting predator-prey interaction.
Despite all the negative effects of noise, humans have had a difficult time agreeing on the best way to address, especially in legislation, the problem of community noise. Most of the problem stems from the nature of noise.
The word “noise” means “unwanted sound.” Unfortunately, the line between wanted and unwanted noise is a matter of personal preference. Just as some people may call certain plants weeds, some people may call certain sounds noise. In many ways, disruption is in the ear of the listener.
There are, however, several noise metrics used in legislation to limit unwanted noise in communities. These community noise metrics differ from community to community and from country to country. In this article, we’ll discuss three of them.
Before we jump in, it is important to remember one thing about community noise: it is impossible to please everyone. There will always be people who are dissatisfied with the level of noise (and usually a specific noise) in a community. There is no way around this. That said, community noise metrics were created as a defense against the rationalizations of those who say to “just deal with it.”
DNL stands for Day-Night Levels (also written Ldn). The DNL metric was created by the US Federal Aviation Administration (FAA) to analyze the impact of airport noise on communities. The DNL is meant to describe the average noise level over a 24-hour period. When calculating DNL, nighttime sound pressure levels (from 10 pm to 7 am) are artificially increased 10 dB before averaging. By “penalizing” nighttime noise, the goal is to decrease noise levels by 10 dB at night so that people can sleep. According to the FAA, a maximum DNL of 65 dB is appropriate for residential areas.
CNEL stand for community noise exposure level. CNEL is a noise metric used in California and works just like DNL, except that it treats evening hours—the time period from 7 pm to 10 pm—separately. These evening hours are artificially boosted 5 dB to account for the transition into quieter nighttime conditions in the community. Night levels (10 pm to 7 am) are boosted 10 dB. After boosting, all levels are averaged to come out with a single CNEL value.
Some European countries use the DENL (Day-evening-night average sound level.) DENL works just like CNEL, boosting evening and nighttime levels, although the hours associated with each period may vary country to country.
A Final Word
If you are concerned about noise in your community, look up your local noise ordinances. These will let you know what, if any, legal structure is already in place to deal with noise problems. Often, solutions to noise problems can be reached through clear and respectful communication. Remember to be courteous and willing to compromise when working out solutions.
Some potential solutions to decreasing community noise include installing noise barriers, changing speed limits, changing road surface textures, limiting heavy vehicles, changing flight paths, engineering quieter engines, shock mounting industrial machines, and factoring time of day in for flights. If the situation is more serious or larger than neighbor-neighbor problems, an acoustical consultant or acoustical engineer may need to be hired to do a community noise impact study. If your community does not have a noise ordinance, you will want to encourage your community to create one with the aid of an acoustical consultant.