Toward a realistic estimate of octave band sound levels for electric transformers
Keywords:Electric transformers, Frequency bands, Manufacture, Textbooks, Measured data, Octave bands, Ontario, Prediction equations, Sound emission, Sound level, Whole body
AbstractThe typical starting point, when evaluating the sound emissions of a proposed transformer, is to obtain the manufacturer's sound level data or develop an estimate using generic prediction equations from a published textbook. If sound level information is available from the transformer manufacturer - whether measured or estimated - it is usually given only in terms of an overall A-weighted ("dBA") value. So, for detailed analysis in octave frequency bands, textbook information is still usually required, in terms of the spectral weightings needed to apportion the single dBA level into its component octave band sound levels. Unfortunately, the information in the published reference texts varies enormously with regard to the suggested spectral weighting corrections. The corrections in some texts are internally inconsistent, and the discrepancy among different texts (even those which cite the same primary references) is severe enough to call the whole body of data into question. This paper enumerates the inconsistencies and discrepancies within and among several commonly used acoustical engineering text books and compares the textbook levels to a wide body of data collected at numerous outdoor transformer installations throughout Ontario. Suggestions are provided for realistic spectral weightings and sound level estimates for transformers, on the basis of the measured data.
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