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umptionsf <br /> 9.A. - Page 108 <br /> cannot hear(e.g., dog whistles and low frequency sounds, such as the groaning sounds emanating <br /> from large buildings with changes in temperature and wind). With A-weighting,calculations and <br /> sound monitoring equipment approximate the sensitivity of the human ear to sounds of different <br /> frequencies. <br /> Some common sounds on the dBA scale are listed in Tableok-1. The relative perceived loudness <br /> of a sound doubles for each increase of 10 dBA, although a 10-dBA change in the sound level <br /> corresponds to a factor of 10 change in relative sound energy. Generally, individual sounds with <br /> differences of 2 dBA or less are not perceived to be noticeably different by most listeners. <br /> Maximum4NoiseaLevele(Lmax): Lmax is the maximum or peak sound level during a noise event. <br /> The metric only accounts for the instantaneous peak intensity of the sound, and not for the <br /> duration of the event. As an aircraft passes by an observer,the sound level increases to a <br /> maximum level and then decreases. Some sound level meters measure and record the maximum <br /> level or Lmax. <br /> SoundcExposureaLevele(SEL): SEL, expressed in dBA, is a time integrated measure, expressed <br /> in decibels, of the sound energy of a single noise event at a reference duration of one second. The <br /> sound level is integrated over the period that the level exceeds a threshold. Therefore, SEL <br /> accounts for both the maximum sound level and the duration of the sound. The standardization of <br /> discrete noise events into a one-second duration allows calculation of the cumulative noise <br /> exposure of a series of noise events that occur over a period of time. Because of this compression <br /> of sound energy,the SEL of an aircraft noise event is typically 7 to 12 dBA greater than the Lmax <br /> of the event. SELs for aircraft noise events depend on the location of the aircraft relative to the <br /> noise receptor,the type of operation(landing,takeoff, or overflight), and the type of aircraft. The <br /> SEL concept is depicted on Exhibitor-2. <br /> TABLE1A-1 <br /> COMMONNSOUNDSZNvTHEv4-WEIGHTEDNDECIBELNECALEv <br /> Sounddevely RelativeJoudnessv Relativevsoundv <br /> Soundv (dBA)v (approximate)v energyv <br /> Rocktmusic,twithtampliferf 1201 64f 1,000,OOOt <br /> Thunder!snowmobilef(operator)f 110f 32f 100,000f <br /> Boilerf shop!powerfmowei 100f 16f 10,000f <br /> Orchestra!crescendofatf25ffeet,fnoisJkitchenf 90f 8f 1,000f <br /> BusIstreetf 80f 4f 100f <br /> Interiorf off departmentf storef 70f 2f 10f <br /> Ord inarJconversation,f3f feet awayf 60f if if <br /> Quietfautomobilesfatflowfspeedf 50f 112f if <br /> Averagefofficef 40f <br /> 1/4f .01f <br /> CitJresidencef 30f 1/8f .001f <br /> Quietfcountr,/residencef 2Of 1/16f .0001f <br /> Rustlef off leavesf 10f 1/32f .00001f <br /> Thresholdfof hearingf Of 1/6/ .000001f <br /> jSOURCEf U.Sf Departmentfoff HousingfandfUrbanfDevelopment,fAircraftfNoisefImpact—PlanningfGuidelinesfforLocalfAgencies,f1972f <br /> SanfCarlosfAirportV A-4 ESAfAirportsf/130753f <br /> ALUCPf W hitef Pape/ Junef2014f <br />