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<br />Background Noise Correction <br /> <br />Figure 2.2 is a graph used to estimate the amount of background noise influencing a <br />measurement, and the corresponding decibel level to be subtracted from the total measurement to <br />determine the decibel level of the noise source being monitored. <br /> <br />Background Noise Correction <br /> <br />E <br />!? <br />u.. <br />"0 <br />Q) <br />1) <br />(ll- <br />~ (ll <br />-- <br />.Do <br />:::Jf- <br />C/) <br />'" <br />Qi <br />.D <br />'13 <br />Q) <br />Cl <br /> <br />10 <br />9 <br />8 <br />7 <br />6 <br />5 <br />4 <br />3 <br />2 <br />1 <br />o <br />o <br /> <br />\ <br />\ <br />\ <br /> '. <br />-, ~ <br /> ~. <br /> ~. <br />-- <br /> <br />1 <br /> <br />2 <br /> <br />3 <br /> <br />4 <br /> <br />5 <br /> <br />6 <br /> <br />7 <br /> <br />8 <br /> <br />9 <br /> <br />10 <br /> <br />Difference Between Total Noise Level and Background Noise <br /> <br />Figure 2.2 <br /> <br />Figure 2.2 is useful in calculating the effect background noise has on the total noise level being <br />monitored. The background noise must be more than ten decibels below the noise level of the <br />source being monitored to have confidence in the accuracy of the measurement. <br /> <br />In certain instances, when a single noise source is analyzed along with other noise sources, <br />Figure 2.2 can be used to isolate the noise source being monitored and calculate its individual <br />noise level. This is done by measuring and recording the total noise level of all sources. Next, <br />the noise source to be isolated is turned off and a noise level reading is taken with all the other <br />existing noise sources in operation. Total noise level is then subtracted from the background <br />noise level. If, for example, the total noise level is 84 dBA, then falls to 80 dBA when the <br />isolated source is turned off, Figure 2.2 can be used to attribute an 82 dBA noise level to that <br />source in the absence of background noise. <br /> <br />8 <br />