Weighted Difference level .28Dw.29 Sound reduction index

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measuring sound reduction index in classroom


the basic index weighted difference level dw. index defined measuring in decibels (db), noise level produced on each side of building element under test (e.g. wall) when noise produced in room on 1 side (or outdoors) , measured both in room noise produced , in room on other side of element under test.


this measurement may carried out measuring levels in octave bands, or in 1/3 octave bands. (the latter used applications). minimum requirements of standards require frequency range 100 hz 3.15 khz measured (16  ⁄3 octave bands). in situations measurements may carried out in bands down 50 hz and/or 10 khz.


the measured levels in each 1/3 octave band (or octave band) source room (or area) (s) compared measured levels in receiving room (r), , difference taken (s-r). produces measured difference level d each frequency band in measured spectrum.


to produce single integer number measured spectrum plotted on graph, , compared against reference curve (defined in iso 717-1 airborne sound insulation, , 717-2 impact sound insulation). reference curve moved in 1 db steps until total of unfavorable deviations (measured points on graph below reference graph) close 32 possible not greater 32.


the value of reference curve @ 500 hz taken weighted difference level, dw considered approximately equal a-weighted level difference observed if normal speech used test signal.







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