Question

7 When a 1.5'x3' window is open, the sound-intensity-level of the street's pois inside the room is 60 dB. When the window is closed, it blocks all the street's noise. (a) What would be the noise-intensity-level inside the room when the window is left slightly open, so that the open area is 18 square inch? (b) What would be the street's noise-intensity-level when the window is open to 18 square inches, if when the window is completely closed the street noise-intensity-level inside the room is 20 dB?

Answer 1

a) Dund intensity levels are calculated in decibals which is related to intensity ß (dB) = 1o log, ) In-rohlma is a lowest threshold intensity for which p=0dB When window of area 0.418 m2 is open sound intensity is 60 dB P = de : to Do3 . )

60 = lo logo lote 5 e = 403, 43 I = 403.43 x 10 W/m² - I = 4,034 x 10" W/m2 He also have relation with a rea as -lb P= Power = 4.034x16 W/m xo.118 m2 P = 1.686 Xio "W When the door is left slightly open with an area 18 Square inch which is equal to 0.0116m² ID I1686 x 10" 1-686 X10 W 0.116 m2 Ig = 145. 34 x10 100 m Pe = 10609 (145.234x261° Py = 1000910 (14534) 16 (4.16 ) = 40.16 dB. B) Now when the window Closed is completely 20 dB = 10lgio ()

er I = 7.389 x 101 wim? This is the new threshold intensity Pe = 10 209,0 (step) p = 1000g, ( ) po tohogn (1.68€ tuoto 1.686 XIO - ) 10 12 0:0116 x 7.389x10 = 10 00910 (19.67 X10%) = 1000g, (1967) IP = 32.9d8 Thus the noice intensity level When window is closed = 32.9dB.