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<br />1# <br /> <br />UsinJ! Decibels <br /> <br />Addition and subtraction of decibels is often necessary for estimating total noise levels or <br />background noise. Because decibels are measured using a logarithmic scale, conventional linear <br />mathematics can not be used. The most convenient way to perform simple arithmetic functions <br />involving logarithmic measurements is to use doubling rules. These rules provide an accurate <br />estimate of the effect distance and multiple sources have on measured sound pressure level. <br /> <br />Distance Attenuation Estimations <br /> <br />When the distance is doubled from a Line source the sound level decreases three decibels. <br /> <br />Example: If a sound level is: <br /> <br />70 decibels at 50 feet it will be <br />67 decibels at 100 feet, and <br />64 decibels at 200 feet. <br /> <br />When the distance is doubled from a Point source the sound level decreases six decibels. <br /> <br />Example: If a sound level is: <br /> <br />95 decibels at 50 feet it will be <br />89 decibels at 100 feet, aud <br />83 decibels at 200 feet. <br /> <br />Distance Attenuation of Noise levels <br /> <br />2d <br /> <br /> <br />4d <br /> <br /> <br />d <br /> <br />95 dBA 89 dBA <br />,\~~)"'O fitJ ~ <br />' I'~"""} <br />.. " 100 ft <br /> <br />83 dBA <br /> <br /> <br />200 ft~ <br /> <br />6 <br />