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5/29/2014 11:39:25 AM
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6/19/2013 3:33:38 PM
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Planning Files
Planning Files - Planning File #
07-063
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-� — <br />, <br />The reference pressure used in acoustic; is twenty (20) inicro Pascals dBA – Sound pressure <br />level expressed in decibels, i'iltered or weighted at the various frequencies is to approximate the <br />response of the human ear. The sound pressure level in decibels is equal to ten (10) times the <br />logarithm (to the base 10) of the ratio between the pressure squared divided by the reference <br />pressure squared. Where L is the level and A an AB are quantities related to power. <br />L = 10 log (A-B } dB <br />Therefore, any time that the word "level" is referred to in acoustics, decibel notation is implied. <br />The example chart below is using a starting point for the human ea�- at OdB. Sound power level <br />(abbreviated as PWL and symbolized LW) would be defined as: <br />LW or PWL = 10 Log (W-Wo) db <br />To bring into perspective different dB levels of co�ninon sounds, please refer to the chart <br />below. This chart demonstrates several comparison soiirces of sound that most persons can <br />relate to. They area as follows: <br />SOURCF, dB �•atin� <br />17U <br />Turbojet Engine <br />160 <br />150 <br />140 <br />75 Piece Orchestra <br />130 <br />120 <br />Large Chipping Hammcr <br />110 <br />Auto on Highway 100 <br />90 <br />80 <br />70 <br />Voice, Conversationa] <br />60 <br />50 <br />40 <br />30 <br />Voice, Very Soft Whisper <br />20 <br />10 <br />U <br />The following chart oives an example oi [he pezception of the human ear to detect change in the <br />dB leveL <br />, <br />
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