Orange County NC Website
Browse       Search
fluctuating noise during that period (with no consideration of a <br /> nighttime weighting. ) It is a measure of cumulative energyL For single <br /> events , L eg used the sound exposure level (SEL) . The SEL!accounts for <br /> the ear's reduced sensitivity to low and very high frequen I cies , but it <br /> employs a simple "A-filter" rather than the complex function used in the <br /> EPHL calculation. Any increased annoyance caused by the pre6ence of pure <br /> tones is not accounted for by this simplified weighting ,lbut SEL does <br /> incorporate the effect of duration. Because the time interial may vary , tor <br /> it should always be specified by a subscript ( such as Leg(8 ) for an ( <br /> 8-hour exposure to workplace noise) or be clearly understood , <br /> L eq(24) SEL + 10 log (Nd + Nr ) - 49. 4 <br /> 04614-17v <br /> Nry•-•e <br /> Day-Night Sound Level (Ldn) <br /> Ldn is Leg with a 10-dB nighttime weighting; it is a measure of <br /> cumulative energy. Ldn , which is similar in concept to NEF, uses the <br /> 411 SEL as the measure of noise from each single event . <br /> Like NEF, Ldn has a weighting for nighttime operations . The reason <br /> for this weighting is the same for both measures - intuitive rather than <br /> purely scientific . <br /> L dn has recently grown in popularity , partly because it is simpler <br /> to measure than NEF. <br /> Ldn SEL + 10 log10 (Nd + 10 Nn) -49 . 4 . <br /> Community Noise Equivalent Level (CNNL) <br /> California has a descriptor similar to Ldn. It is the Community <br /> Noise Equivalent Level (CNEL ) , which adds an evening period - 700 to <br /> 10 :00 p .m . .. during which events are assumed to be 5 dB more noisy. To <br /> 410 <br /> 20 <br /> -400 'or ' <br />