BUILDING PHYSICS 17 Calculation of the air-borne sound insulation value R’w with consideration of the secondary paths Based on the above described individual values, the following can be calculated by means of the formula R’w: According to DIN 4109, 2 dB must be considered as forecast unreliability for the air-borne sound: R’w = 57.3 dB – 2 dB = 55.3 dB > measured R’w = 55 dB Proof of the air-borne sound is thereby provided. REMARK regarding RDf and RFd These flank insulation values are far above the value of the flank paths RFf due to the decoupled insulation levels. For simplification, this path can be neglected in the execution of double-sided installation levels (stand-alone or on vibration mounts) on the apartment partition wall or on the interior side on the flanking wall. In the calculation example shown above, the difference when neglecting these flank paths is +0.3 dB for R’w . Vertical sound transmission via the apartment separating ceiling Footfall sound transmission in consideration of secondary paths The measured standard footfall sound level of the apartment partition wall (complete assembly Rw = 69 dB) can be inserted directly in the formula below: The footfall sound flank transmissions on the path Df and DFf are to be calculated: The lab value for the flank transmission of the footfall sound on the path Df is to be calculated according to the following formula: R’w = –10 log(10 -0,1×69 + 10-0,1×61,6 + 10-0,1×75,1 + 10-0,1×75,1 + 10-0,1×61,6 + 10-0,1×75,1 + 10-0,1×75,1 + 10-0,1×66,8 + 10-0,1×82,8 + 10-0,1×82,8 ) = 57.3 dB 1 L’n,w = 10 lg(10 0,1L n,w + ∑10 0,1L n,ij,w) 2 Ln,Df,w = Ln,Df,lab,w – ∆Kij – ∆Rj,w – 10lg (Ss / (lo lf)) Ln,DFf,w = Ln,DFf,lab,w – ∆Kij – ∆Rij,w – 10lg (Ss / ( lo lf)) 4 5 L’n,Df,lab,w = 10 lg(10 0,1(L n,w + K 1 ) – 10 0,1L n,w) 6
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