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B. Dav-Night Level (DNL) <br /> Noise levels utilized in the standards are described in terms of the Day-Night <br /> Level (DNL). The DNL rating is determined by the cumulative noise exposures <br /> occurring over a 24-hour day in terms of A-Weighted sound energy. The 24-hour day is <br /> divided into two subperiods for the DNL index. i.e., the daytime period from 7:00 a.m. to <br /> 10:00 p.m., and the nighttime period from 10:00 p.m. to 7:00 a.m. A 10 dBA weighting <br /> factor is applied (added) to the noise levels occurring during the nighttime period to <br /> account for the greater sensitivity of people to noise during these hours. The DNL is <br /> calculated from the measured Leq in accordance with the following mathematical <br /> formula: <br /> DNL = [(Ld+l01ou1015) & (1_11+10+101°g 09)] - l0log1024 <br /> Where: <br /> Ld = Leq for the daytime (7:00 a.m. to 10:00 p.m.) <br /> Ln= Leq for the nighttime (10:00 p.m. to 7:00 a.m.) <br /> 24 indicates the 24-hour period <br /> denotes decibel addition. <br /> C. A-Weighted Sound Level <br /> The decibel measure of the sound level utilizing the "A" weighted network of a <br /> sound level meter is referred to as "dBA". The "A" weighting is the accepted standard <br /> weighting system used when noise is measured and recorded for the purpose of <br /> determining total noise levels and conducting statistical analyses of the environment so <br /> Mat the output correlates well with the response of the human ear. <br /> B- <br />