Ex. E <br />West <br />-9.7 dB, <br />essentially -10 dB because of increased distance to the property line. <br />Baffling Effect: This is a - <br />material in the generator room plus the noise attenuating effect of each acoustic louver/hood <br />opening. There is no accounting as to how this -17 dB muffler effect per opening is derived. <br />Sound Barrier Effect: The SW corner of the building addition casts an acoustic shadow, blocks <br />generator and AC unit noise from direct illuminating the nearby western property line. A -15 dB <br />ccount for the shadowing effect. However it is introduced <br />simply as a number, otherwise a non-defined, non-calculated sound barrier/sound berm effect. <br />Building Reflection: Absent from the description of the building corner sound barrier effect is <br />any -on equipment room and <br />centered along the face of the addition. This building reflects westerly moving noise that <br />otherwise would have expanded away from the area, back into the shadow zone. The building is <br />additionally somewhat angled inward, serving to even further infill the shadow zone. <br />Neglecting the backfill reflection, SSA estimates that each air vent in the wall of the generator <br />room will deliver 80 10 17 15 = 38 dB to the neigh <br />deliver 38 + 38 = 41 dBA at the property line. Left out of the SSA calculation is a reduction of <br />overall attenuation by about 7 dBA, raising property line noise level from 41 to 48 dBA. <br />South <br />To the south of the generator room, there lies no obstruction, outside of the play structures which <br />om and only <br />shadowed by the shed. This effect is not discussed in the SSA report but a curious -10 building <br />attenuation factor does show up in their calculation. <br />The SSA calculation begins with the distance factor as with the West calculation: -20 Log200/23 <br />=-18.9 = -19 dB. Then it adds the Noise control factor as before of -17 dB. The combination <br />from one of the openings is 80 19 17 = 44 dBA. The calculation for the other opening is <br />confusing; it includes all of the above plus a -10 dB Building Factor, typically associated with <br />the sound barrier effect due to buildings blocking the noise path. For the second window the <br />attenuation factors are 80 19 17 10 = 34 dBA but instead the sum is stated to be 43 dBA. <br />For both windows we have 44 + 43 = 46.5 dBA <br />It might be a TYPO (43 instead of 34) or possibly SSA averaged out the sound shadowing effect <br />of the play structure, by applying -1 dB to the whole of the properties to the south instead of -10 <br />for a section of one property and -0 for the rest. Again, the thinking behind the SSA calculation <br />is not explained. <br />8 <br />