Orange County NC Website
Browse       Search
46 <br />WE <br />5 Discussion <br />Non- Co=hance Sound Pressure Levels <br />The noise generated in the 50 -80Hz, 630Hz, and 2-6 3kHz 1/3 octave bands do not exceed the <br />ambient conditions by the minimum 6 dB required by the ISO -3744 Standard The published levels <br />in these bands should be considered to be the upper boundary of the exact level — the true level is <br />likely to be lower in level than the calculated values The overall sound power level, LwA, does meet <br />the requirements of the ISO -3744 Standard, in terms of ambient noise However, the acoustical <br />environment does not meet the ISO -3744 Standard in any of the 1/3 octave bands Therefore, the <br />published levels in all of the bands, including the overall LwA, should be considered as the upper <br />boundary of the actual level <br />Configurations <br />There was no significant difference in sound power level between the configurations The only <br />statistically important variation was the amplitude of a 9kHz tone, which was highest with <br />Configuration 2 This tone could be a sub - harmonic of the switching circuitry, which runs at <br />18kHz <br />Noise Modeling <br />In all of the configurations tested, the relatively broadband noise from the blower dominated the <br />noise character There is also significant tonality at the 160 Hz band from the blower The <br />directionality in the noise generation appears to be modest, with all four sides fitting within a 2 dB <br />window The relatively uniform directivity is due to the presence of air inlets or outlets on all four <br />sides as well as at the bottom of the inverter As there are no openings in the top of the inverter, <br />the levels at the top typically measured 7 dB lower than the sides of the unit <br />With the configurations tested, we would model the unit as a box with uniform directivity at an <br />elevation of approximately 1m <br />Please feel free to call if you have any questions, we may be reached in our San Francisco office by <br />telephone at ( +1) 415 - 693 -0424 or via email at Mler@yg-constilt.co <br />Sincerely, <br />7� �4/� <br />Tyler Rynberg, PE <br />Vibro - Acoustic Consultants <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 />