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Enbridge Energy, LP Hoover& Keith, Inc. Waterloo Pump Station — Noise Impact Analysis RN 3083/JN 4796 APPENDIX C—Acoustical Terminology (10/10/14) (3) Human Perception of Change in Sound Level ➢ A 3 dB change of sound level is barely perceivable by the human ear ➢ A 5 or 6 dB change of sound level is noticeable ➢ If sound level increases by 10 dB, it appears as if the sound intensity has doubled. (4) Background or Ambient Noise: The total noise produced by all other sources associated with a given environment in the vicinity of a specific source of interest, and includes any Residual Noise. (5) Sound Pressure Level (LP or SPL): Ten times the common logarithm to the base 10 of the ratio of the mean square sound pressure to the square of a reference pressure. Therefore, the sound pressure level is equal to 20 times the common logarithm of the ratio of the sound pressure to a reference pressure(20 micropascals or 0.0002 microbar). (6) Octave Band SPL: Sound is typically measured in frequency ranges (e.g., high-pitched sound, low-pitched sound, etc.)that provides more meaningful sound data regarding the sound character of the noise. When measuring two noise sources for comparison, it is better to measure the spectrum of each noise, such as in octave band SPL frequency ranges. Then, the relative loudness of two sounds can be compared frequency range by frequency range. As an illustration, two noise sources can have the same dBA rating and yet sound completely different. For example, a high-pitched sound concentrated at a frequency of 2000 Hz could have the same dBA rating as a much louder low-frequency sound concentrated at 50 Hz. (7) Daytime Sound Level(Ld) & Nighttime Sound Level (Ln): Ld is the equivalent A-weighted sound level, in decibels, for a 15 hour time period, between 07:00 to 22:00 Hours (7:00 a.m. to 10:00 p.m.). Ln is the equivalent A-weighted sound level, in decibels, for a 9 hour time period, between 22:00 to 07:00 Hours(10:00 p.m. to 7:00 a.m.). (8) Equivalent Sound Level (Leg): The equivalent sound level (Leg) can be considered an average sound level measured during a period of time, including any fluctuating sound levels during that period. In this report, the Leg is equal to the level of a steady(in time)A-weighted sound level that would be equivalent to the sampled A-weighted sound level on an energy basis for a specified measurement interval. The concept of the measuring Leg has been used broadly to relate individual and community reaction to aircraft and other environmental noises. (9) L-Percent Sound Levels: The L percent levels (e.g., L5o, Lso& Lio) refer to the A-wt. sound levels that are exceeded for 90, 50 and 10 percent of the time, respectively, during a measurement period. For example, the 90-percentile exceeded sound level, designated to as Lso, is the A-wt. sound levels that are exceeded for 90 percent of the time and is considered the typical lowest anticipated sound levels. The range between the Lio and Lso values usually provides a good indication of the variability of the sound levels during the period of measurement. C-2