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9.A. - Page 105 <br /> APPENDIXAv <br /> Noise Modeling Assumptions <br /> Al NEnvironmentahNoiseiundamentalsv <br /> Noise is defined as unwanted sound. Sound,traveling in the form of waves from a source, exerts <br /> a sound pressure level(referred to as sound level)which is measured in decibels(dB),with zero <br /> dB corresponding roughly to the threshold of human hearing, and 120 to 140 dB corresponding to <br /> the threshold of pain. Pressure waves traveling through air exert a force registered by the human <br /> ear as sound. <br /> Sound pressure fluctuations can be measured in units of hertz(Hz),which correspond to the <br /> frequency of a particular sound. Typically, sound does not consist of a single frequency,but <br /> rather a broad band of frequencies varying in levels of magnitude(sound power). When all the <br /> audible frequencies of a sound are measured, a sound spectrum is plotted consisting of a range of <br /> frequencies spanning 20 to 20,000 Hz. The sound pressure level,therefore, constitutes the <br /> additive force exerted by a sound corresponding to the sound frequency/sound power level <br /> spectrum. <br /> The typical human ear is not equally sensitive to all frequencies of the audible sound spectrum. <br /> As a consequence, when assessing potential noise impacts, sound is measured using an electronic <br /> filter that de-emphasizes the frequencies below 1,000 Hz and above 5,000 Hz in a manner <br /> corresponding to the human ear's decreased sensitivity to extremely low and extremely high <br /> frequencies. This method of frequency weighting is referred to as A-weighting and is expressed <br /> in units of A-weighted decibels (dBA).A-weighting follows an international standard <br /> methodology of frequency weighting and is typically applied to community noise measurements. <br /> Some representative noise sources and their corresponding A-weighted noise levels are shown on <br /> ExhibitAA-1. <br /> SanfCarlosfAirportV A-1 ESAfAirportsf/130753f <br /> ALUCPfWhitefPape/ Junef2014f <br />