Ex. E <br />15 dB attenuation for both inlet and outlet louver. SSA used 17 dB for their room + louver <br />attenuation effect. In the present analysis, both inlet and out vents are assumed through acoustic <br />louvers. <br />The south wall of the generator room will have two large louver sets, each one will b <br />combined louver area of 30 sqft. On the engine side of each <br />louver is a noise level of 99 dBA and the louver supplies 15 dB attenuation. This produces 30 <br />sqft of 84 dB,A noise emanating out of the generator building, an overall sound power noise <br />source of 88.5 dBA. <br />To this we have to add the fact that the louvers are in a wall, and not an elevated point noise <br />source out in the open. We have to add 3 dB for the wall megaphone effect and another 3 dB for <br />the ground reflection effect, overall +6 dB. After adjusting for distance the three readings will be <br />57dBA to the west, 48 dB,A to the dB,A to the east. <br />To the West, the house is around the corner of the building and if we allow a 15 dB barrier effect <br /> 15 = 42 <br />dB,A, close to the 41 dB,A predicted by SSA. <br />To the South, there is no noise mitigating element between the generator room and the homes to <br />the south and the 48 dBA figure remains the predicted impact. <br />To the East there is a picket fence located around the tower location which has been assigned -6 <br />dB sound barrier effect by SSA, which reduces generator noise to the east down 43.5 6 = 37.5 <br />dBA. <br /> <br />Comparison: Single Number Estimates <br /> <br /> SSA Basic <br /> 41 42 <br /> 46.5 48 <br /> 33.6 37.5 dBA <br />Clearly the SSA calculation and the Basic calculations are fairly close. However, when the <br />octave band version of the Basic calculation is performed, then the SSA prediction falls more <br />than 10 dB behind the more accurate model prediction as seen in the next section. <br />(iii) Octave Band Generator Room Calculation <br />A third method to do this calculation is to use sound levels in each octave to perform the <br />calculation. This is similar to the above simplified version except instead of one calculation; we <br />use 8 simultaneous calculations, one for each octave between 63 Hz and 8k Hz and then add up <br />all 8 results to get the overall final result. <br />10 <br />