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.. <br /> 1 <br /> If there are several levels of the same value to be added together <br /> - several engines , all measured at 85 dB , for instance - add them this <br /> way: <br /> TABLE 3. METHOD FOR ADDING SEVERAL LEVELS OF THE SAME VALUE. <br /> NO. of Equal Add to that <br /> Levels Level <br /> 2 3dB <br /> 3 5dB <br /> 4 6dB <br /> 5 7 dB <br /> 6-7 8dB <br /> 8 9dB• <br /> 9-10 10 dB <br /> N 10 log N dB <br /> 411 <br /> Up to now, we have discussed the addition of 1 ev el s from events <br /> that occur at one time: for example , several airplanes warming up on the <br /> same ramp . We are adding energy from these simultaneous events. Later , <br /> we will be considering aircraft noise exposure from a series of events <br /> occurring at different times , such as the sequence of aircraft arriving <br /> for landings on a single runway. We will , however , add the energy of <br /> events that occur at different times in the same way we ad energy <br /> of simultaneous events . <br /> The second characteristic of sound is frequency , often referred to <br /> as "pitch ." <br /> 410 <br /> 9 <br /> 7,-,51!Anmv.m%:71#10.*1”771r""—' " : , _ <br />