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*:/ : 11-1 h WA <br />■ Noise. Sound that is loud, unpleasant, unexpected, or otherwise undesirable. <br />■ Decibel (dB). A unitless measure of sound on a logarithmic scale. <br />■ A -Weighted Decibel (dBA). An overall frequencyweightedsound level in decibels that approximates the <br />frequency response of the human ear. Equivalent Continuous Noise Level (LQ. The fa efgy-average noise <br />level over a specified measurement period (typically one hou). The Ley metric is a single numerical value <br />that represents the equivalent amount of variable sound energy received by a receptor over the specified <br />duration. <br />■ Equivalent Continuous Noise Level (I.J; also called the Energy -Equivalent Noise Level. The <br />value of an equivalent, steady sound level which, in a stated time period (often over an hour) and at a stated <br />location, has the same A -weighted sound energy as the time -varying sound. Thus, the IRq metric is a single <br />numerical value that represents the equivalent amount of variable sound energy received by a receptor over <br />the specified duration. <br />■ Statistical Sound Level (L„). The statistical sound levels, or n-exceeded sound levels, are noise metrics <br />that represent fractional percentages of the measurement period that are exceeded for `n' percent of the <br />time. For example, the Lso noise level represents the noise level that is exceeded 50 percent of the time (i.e., <br />half the time the noise level exceeds this level and half the time the noise level is less than this level). This <br />level is also representative of the level that is exceeded 30 minutes in an hour. Similarly, the Lot, Los, and <br />Les represent the noise levels that are exceeded 2, 8, and 25 percent of the time, respectively (of 1, 5, and <br />15 minutes per hou). These statistical sound levels are typically used to demonstrate compliance with a <br />noise ordinance for stationary noise sources. <br />■ Community Noise Equivalent Level (CNEL). The energy average of the A -weighted sound levels <br />occurring during a 24-hour period with 5 dB added to the sound levels occurring during the period from <br />7:00 PM to 10:00 PM and 10 dB added to the sound levels occurring during the period from 10:00 PM to <br />7:00 AM. <br />■ Sensitive Receptor. Noise- and vibration -sensitive receptors include land uses where quiet envifonments <br />are necessary for enjoyment and public health and safety. Residences, schools, motels and hotels, libraries, <br />religious institutions, hospitals, and nursing homes are examples. <br />■ I.. The maximum root -mean -square noise level during a measurement period. <br />■ Peak Particle Velocity (PPV). The peak fate of speed atwhich soil particles move (e.g., inches per second) <br />due to ground vibration. <br />■ RCNM. Federal Highway Administration Roadway Construction Noise Model. <br />75C-103 <br />