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; <br /> (. . <br /> t. <br /> Alternatively , use the following figure. <br /> 0 <br /> -a 3 <br /> 4:741 1111111111111111 MI <br /> ; <br /> , cticg 1 <br /> 0,114 <br /> U■1"1" 2 <br /> ill 1=116 <br /> 00 <br /> z E <br /> II= <br /> Ill Ill <br /> mow— <br /> x 0 1 <br /> litg::Fis 111111121111111111 <br /> mmilimmiliminin <br /> 1111 <br /> 0 imm......- <br /> 0 2 4 6 8 10 12 14 16 18 20 <br /> i <br /> DIFFERENCE IN DECIBELS <br /> BETWEEN TWO LEVELS TO BE ADDED <br /> FIG 2. METHOD 2: ADDING DECIBELS. <br /> The combined noise of the two engines , then , is 101 dB. <br /> When there are several decibel levels to be added , add them two at <br /> a time , starting with the lower valued levels and continuing , two at a <br /> time , until only one value remains . To illustrate , suppose that the <br /> sound levels of five fans , side by side in a mechanical room, are 68 dB , <br /> 75 dB, 79 dB, 82 dB , and 88 dB , respectively. They would be added this <br /> way : <br /> 68 dB222> <br /> = 76 <br /> 75 dB <br /> = 81 <br /> 79 dB <br /> ------. . . 85 <br /> 82 dB—.---...----....— <br /> = 90 dB <br /> 88 dB----------- <br /> 0 <br /> 8 <br />