lindab | we simplify construction Overflow unit OLC Technical data Sample calculation When dimensioning an overflow diffuser, calculate the decrease in the wall’s noise-reducing properties. For these calculations, the area of the wall and sound reduc- tion figure R must be known. This is adjusted in relation to the unit’s D n,e value. D n,e is the unit’s R value given at a transmission area of 10 m 2 , as speci- fied in ISO 140-10. The D n,e value can be converted into the R value for other transmission areas using the table below. A rea [m 2 ] C orrection [dB] 10 2 1 0 -7 -10 The diagram below indicates the decrease of the sound reduc- tion index of the wall, for a given octave band value (D n,e ) or weighted value ( D n,e,w ). As a rough estimate the calculation can be performed directly using the wall´s Rw value and the weighted elementnormalized level difference D n,e,w of the unit. Example: (See diagram below) : R w (wall): D n,e,w (diffuser): Area of wall: 50 dB 44 dB 20 m 2 Number of Units: 1 R w - D n,e,w = 6 dB 20 m 2 /1 = 20 m 2 Indicated reduction of R w (wall): R w value for wall with unit: 5 dB ~50-5 = 45 dB The calculation can also be performed using the following for- mula: R res = 10 Log S wall + (10m² 10 -0,1·Dn,e ) (S wall 10 -0,1 · Rwall ) where: - R res is the resulting reduction figure for wall and diffuser. - S is wall area. - D n,e is the unit’s D n,e value. - R wall is the wall’s R value without unit. Reduction of wall (R w ) [dB] 25 20 15 10 5 0 0 5 10 Difference between wall and unit ( R w - D n, e, w ) [dB] 20 15 10 5 0 15 20 25 30 35 40 45 50 Area of wall [m²] / Number of units [-] 4 Lindab reserves the right to make changes without prior notice 2021-03-11
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