Ex. E <br />1) The generator manufacturer does supply octave band sound levels at 23 <br />overall 108 dBA level. The engine creates more low frequency noise than high frequency noise. <br />2) The some 400 sqft of sound absorption used in the generator room absorbs the high <br />frequencies pretty well but not much in the low frequency range. Manufacturer data provides <br />how much absorption in each octave band. <br />3) Finally, the louvers are also rated in octave bands, again not much absorption in the lower <br />frequency range and much more in the upper frequency range. <br />Octave Band Assessment of Generator Noise Impact <br /> <br />level63 Hz1252505001k2k4k8k <br />63.969.470.772.872.673.970.963.580 dBA <br />+28= Lw91.997.498.7100.8100.6101.998.992.5108 <br />% absorb0216186971011.031.0 <br />Sqft absor083242341384400408396%x396=A <br />-10LogA0-3.0-7.5-9.0-9.5-9.7-9.9-9.6 <br />Lreverb91.994.491.291.891.192.289.082.9Lw-10LogA <br />Ldirect 83.388.990.292.392.193.490.484Lw-8.5 <br />Lp92.595.593.795.094.695.992.786.5Lr+Ld <br />Louver -6-6-7-10-15-20-19-20TL (dB) <br />Lp outside86.589.586.785.079.675.973.766.5Lp-TL <br />+4.5=Lw91.094.091.289.584.180.478.271.098.1 dBA <br />Equations used in the above calculation: <br />Lw = Lp + 20 Log r + 0.6 = Lp + 20 Log 23 + 0.6 = Lp + 27.8 = Lp + 28 <br />Lreverb = Lw 10 LogA + 16.3, A= sqft sabines <br />Ldirect = Lw -20LogR + 0.6 = Lw <br />Lp = Lreverb + Ldirect <br />Lw = Lp + 10Log30 10.3 = Lp + 4.5 (feet) <br />The net result is that the 2 louvers combined produce Lw = 98.0 dBA which is about 10 dB <br />louder than the 88.5 dBA calculated previously. (The result of the 88.5 dBA calculation resulted <br />in a prediction of 42 dB,A at the West property line, which is close to the prediction of 41 dB,A <br />by SSA.) The octave based assessment for noise emitted out of the two vent openings raised the <br />noise output by 10 dB. Leaving all other factors the same; the Q = +6 dB megaphone effect, the <br />distance and the sound barrier effects as before, the net result is 10 dB louder in all directions. <br />To the We: 41 + 10 = 51 dBA <br />: 48 + 10 = 58 dBA, and <br />To the East would be: 43 + 10 dBA = 53 dBA. <br />The significant difference in the results is due to octave band analysis. There are two factors that <br />influence the audible sound emitted out the generator windows. One is that the absorption <br />coefficient for the sound absorbing materials in the generator room are effective 500 Hz and <br />above. Secondly, but similarly, the Louvers are only effective in the higher frequency range, <br />11 <br />