For land use planning, DNL is usually averaged over a year to include days of light and heavy training loads, as well as periods with no activity. DNL represents an average of all noise activities conducted throughout the day, and is usually averaged over an extended period of time. C-weighted DNL is used to describe low-frequency sources such as large caliber weapons and detonations. A-weighted DNL (ADNL) is used to describe noise from sound sources such as aircraft or transportation. As with the decibel, DNL can also be weighted to better describe sound based on the type of the source. The military uses DNL as the basis for determining land use compatibility for noise associated with aviation, demolition, and large caliber weapons. " Day-night average sound level " (DNL) is the most widely-used metric to describe, assess, and predict long-term noise exposure. The 10-dB penalty considers that people are more sensitive to noise during these hours, when sounds are more noticeable and may be considered more intrusive. Day-Night Average Sound Levels Day-Night Average Sound Level (DNL)ĭNL is a 24-hour average sound level that includes a 10-dB adjustment, or "penalty", for activity occurring between 10 p.m. The differences in these metrics often confuse both installation personnel and communities, who may not realize that different types of noise are assessed in different ways. Each metric or measurement is used differently depending on the source or type of sound to ensure community exposure is appropriately measured and addressed. Single Event Sound Levelsįederal, state, and local agencies use a set of common metrics and measurements to describe noise when assessing land use compatibility and conducting noise studies and noise management. As a result, large caliber weapons firing, and detonations are assessed with C-weighted dBs to better describe the sound and vibrations that people may experience. Although people cannot hear low frequencies well, they may feel vibrations that low-frequency energy generates. Common Sounds and Noise Levels (A-weighted) Noise Source (at a given distance)Ĭ-weighted decibels (dBC) quantify sounds containing large amounts of low- frequency energy. This vibration may cause annoyance and concern however, it is very unlikely that vibration from normal military activities will result in structural damage to homes. While artillery firing or explosives activities may seem to shake the ground, the vibration felt in neighbors' homes is typically caused by airborne sound waves that act on external surfaces of a home, causing it to vibrate. For reference, a normal voice has a sound level of approximately 60 dBA, and a busy highway can have a noise level of over 85 dBA. The military typically uses A-weighting to describe sound from generators, aircraft, and general transportation. The A-weighting corresponds to the ear's sensitivity and deemphasizes very high and low sound frequencies to only reflect the frequencies that people actually hear. Most common sound sources are measured using A-weighted decibels (dBA). The standard for the loudness of sound or noise levels is a quantity known as the " decibel (dB)." The human ear is not uniformly sensitive to all frequencies of sound. Establishing a basic and common understanding of noise concepts helps military installations and surrounding communities work together to address noise issues more effectively. While noise itself is something that everyone has experienced and recognizes, the technical concepts applied in noise management can be difficult for installation personnel and communities to understand.
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