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Enbridge Energy, LP Hoover & Keith, Inc. <br /> Waterloo Pump Station — Noise Impact Analysis RN 3083/JN 4796 <br /> APPENDIX C—Acoustical Terminology (10/10/14) <br /> Summary of Acoustical Terminology, Typical Metrics for Regulating Environmental Noise <br /> and Sound Levels for Typical Activities <br /> (1) Decibel (dB):A unit for expressing the relative power level difference between acoustical or <br /> electrical signals. It is ten times the common logarithm of the ratio of two related quantities that <br /> are proportional to power. When adding dB or dBA values,the values must be added <br /> logarithmically. For example,the logarithmic addition of 35 dB plus 35 dB is 38 dB. <br /> (2) A-Weighted Sound Level(dBA):The A-wt. sound level is a single-figure sound rating, expressed in <br /> decibels(Re 20 µPa), which correlates to the human perception of the loudness of sound. The <br /> dBA level is commonly used to measure industrial and environmental noise since it is easy to <br /> measure and provides a reasonable indication of the human annoyance value of the noise. The <br /> dBA measurement is not a good descriptor of a noise consisting of strong low-frequency <br /> components or for a noise with tonal components. <br /> The A-weighted curve approximates the response of the average ear at sound levels of 20 to 50 <br /> decibels. The following are the relative response of A-weighted filter per octave band frequency, <br /> and a graph/curve is provided that shows a graphical representation of the A-wt. filter response <br /> per frequency(in Hz). <br /> 31.5 63 125 250 500 1,000 2,000 4,000 8,000 16,000 <br /> Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz <br /> -39.4 dB -26.2 dB -16.1 dB -8.6 dB -3.2 dB 0 dB +1.2 dB +1.0 dB -1.1 dB -6.6 dB <br /> RELATIVE RESPONSE, <br /> I dB <br /> 10 <br /> 0 �\\ A <br /> B C <br /> -10 <br /> B ./ <br /> -20 <br /> -30 <br /> -40 <br /> A <br /> -50 <br /> 16 31.5 63 125 250 500 1000 2000 4000 8000 16,000 <br /> FREQUENCY,Hz <br /> C-1 <br />