Part 150 CAC Group and Meetings July 1998 Glossary of Common Acoustic and ATC Terminology

Decibel (dB) -is. the unit of soc;hd pressure used to measure noise. Decibel means 1 /10 of a Bell, after Alexander Graham Bell ,(thus the capital B). 'Because'decibels are such a small m'easure, they are computed logarithmical'ty and cannot bd added arithnetically. ' An increase often dB is perceived by human 'ears qs a doubling of ng)ise. dBA or A Weighted decibels adjusts the sound presgure to CQnforp with the’ frequency responseg of the' human ear. Airport noise is almost always measured in dBA. dBC or C weighted decibels adjust:g the.sound pressure tq reflect the lower frequency bands. measure such things as engine run ups and reverse thrugt noise. C weighting can be used to DNL is day/night noise level which was previously known as Ldn, This is a 24 hour average hourly noise level with a 10 decibel (dB) penalty for.nighttime noige events between 10 PM and 7 AAA. DNL contour is the ''map” of noige exposure ,around 'an ajrport. It is c6mputed through an FAA model called the Integrated Noise Model (INM) which calculates the annual noise exposure from an input consisting of the actual fleet operated at'the airport, the runway use, number of operations, and One- 6f day. FAA defi’nes significa-nt noise exposore as any area within the 65dB DNL con{our; that is the area within an anndat average. noise exposure of 65 decibels or higher. Sing-lb Event Noise is the total noise emitted by one overflight or aircraft. Each single event will have a total noise…

Open full document