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EX_SoundIntensity - ARC 4620 Environmental Technology 2 Lab...

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ARC 4620 Environmental Technology 2 Lab Session: Acoustics Sep. 9, 2003 SOUND INTENSITY ( I ): w/m 2 Inverse square law : sound intensity is inversely proportional to the square of the distance from the source. Proof of the second formula : 2 1 1 4 d W I π = Æ W ….. (1) 2 1 1 4 d I π = 2 2 2 4 d W I π = Æ W ….. (2) 2 2 2 4 d I π = (1) = (2). Thus, we have 2 2 2 2 1 1 4 4 d I d I π π = Therefore, we finally equate 2 1 2 2 2 1 d d I I = SOUND INTENSITY LEVEL ( L I ) AND DECIBEL (dB) I = intensity, w/m 2 I 0 = 10 -12 w/m 2 , the threshold of hearing SIMPLIFIED DECIBEL ADDITION METHOD 0 – 1 2 – 3 4 – 8 9 or more 3 2 1 0 1
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ARC 4620 Environmental Technology 2 Lab Session: Acoustics Sep. 9, 2003 Determine the sound intensity ( I ) of a sound whose sound intensity level ( L I ) is 83dB. Solution : [ ] [ ] 12 log 10 10 log log 10 10 log 10 log 10 12 12 0 + = = = = I I I I I 83 Æ 8 12 log 3 . + = I Æ log 7 . 3 = I Æ 2 7 . 3 / 10 m w I = Determine the sound intensity level ( L I ) of a sound whose sound intensity ( I ) is 0.0025 w/m 2 .
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