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OTHER WEIGHTING FACTORS CONSIDERED <br />The NRL required by the Noise Compatibility Guidelines is specified in dBA, <br />while structural elements are to be specified in STC. Therefore, a number of <br />factors must be considered to convert the collection of individual building <br />element STC values to an overall building shell NRL that is specified in terms <br />of dBA. These factors are: <br />1. Noise Source Spectrum: Aircraft <br />While actual spectra for takeoff and landing vary with the type of <br />aircraft, operating conditions and meteorology, the aircraft noise spectrum <br />used by Tocci et al. (see "References") is an acceptable reference <br />spectrum for purposes of this Guide. The use of an aircraft spectrum to <br />estimates sound transmission through a wall is especially important since <br />the low frequency components are not adequately addressed by the STC <br />methodology. <br />2. Composite Wall STC Value <br />The standard procedures for determining the effective transmission value of <br />a composite wall has been followed here (see Figure C-1). <br />Instructions on we of graph <br />1. Subtract the STC value of the door, <br />window or opening from the STC value of the <br />wall. <br />2. Enter the vertical axis of the graph at the <br />point that matches the value from step 1. <br />3. Read across to the curve that represents <br />the percentage of the total area of the wall <br />that is taken up by the door, window, or <br />opening. <br />4. Read down to the honzontal axis. <br />5. Subtract the value on the honzontal axis <br />from the onginal STC value of the wall. The <br />result is the composite STC value of the wall <br />and the door, window or opening. <br />Source: <br />The Noise Guidebook <br />U.S. Dept. of Housing and <br />Urban Development <br />Figure C-1 <br />lte <br />so <br />F <br />1 <br />t% <br />ton <br />1 s, <br />3 3130% <br />a <br />2' <br />a <br />1 50% <br />1• <br />t00% <br />1 3 3 5 <br />10 20 <br />Weltela to ba wanetaa Iran STC e1 evilto <br />oaa. ewArm STC a aMlw ato Winer <br />30 50 <br />'CO <br />44 <br />