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45 <br />-3- <br />inverter were removed This roof deck is approximately 2 8m above the suspended ceiling, <br />providing a vertical clearance of 3 9m <br />The temperature in the fabrication area was estimated to be 22 °C The relative humidity was typical <br />of an indoor air - conditioned environment <br />4.3 Qualification of Acoustical Environment <br />Ambient Noise Correction Factor K1 <br />In the majority of 1/3 octave bands, the ambient noise levels were greater than 6 dB below the test <br />conditions In the 50-80Hz, 630Hz, and 2 -6 3kHz 1/3 octave bands, the ambient noise was <br />frequently only 1 -4 dB below the test conditions Generally, the "middle" four measurement <br />positions had a greater signal -to -noise ratio than the "top" five positions <br />Acoustical Correction Factor K� <br />The reflecting plane extended a minimum of 4 5m from the measurement surface in all directions, <br />which meets the ISO -3744 Standard for the 50 Hz lower boundary of the presented data The <br />reflecting plane was concrete slab -on -grade and was estimated to have an absorption coefficient of <br />0 05 or less in the frequency bands of interest <br />The Approximate Method was used to determine the environmental correction factor, K2 Our <br />calculations show that the highest value for K2 is 9 6 dB and occurs in the 500Hz octave band The <br />environment does not meet the ISO -3744 Standard requirement of K2 < 2 dB The following table <br />presents the calculated octave band K2 values <br />Calculated <br />63 Hz <br />125 Hz <br />250 Hz <br />500 Hz <br />1 kHz <br />2 kHz <br />4 kHz <br />8 kHz <br />K2 <br />52dB <br />46dB <br />68dB <br />96dB <br />93dB <br />86dB <br />71 dB <br />62dB <br />While the values for K2 exceed the ISO Standard in all octave bands, the Standard allows for <br />compliance by using a maximum correction factor of 2 dB Values for which the correction factor is <br />limited to 2 dB therefore represent a "worst- case" or upper boundary for the actual performance of <br />the device under test <br />4.4 Data Presentation <br />Data are presented in Tables 1-7 For each configuration, we present the overall A- weighted (LwA) <br />and the un- weighted 1/3 octave band sound power levels in decibels referenced to 1x1012 W We <br />also present the overall A- weighted (dBA) and the un- weighted 1/3 octave band sound pressure <br />levels in decibels referenced to 20 µPa for each configuration <br />VIBRO- ACOUSTIC CONSULTANTS • 490 POST STREET, SUITE 1427 • SAN FRANCISCO, CA • 94102 • USA <br />PHONE ( +1) 415 - 693 -0424 • FAX ( +1) 415 - 693 -1398 • INTERNET http. / /www.va- consult com <br />