BUILDING PHYSICS 21 5. Calculation of the footfall sound transmission in consideration of secondary paths Calculation L’n,w by means of the following formula According to DIN 4109, 3 dB must be considered as forecast unreliability for the footfall sound: L’n,w = 43,0 dB + 3 dB = 46.0 dB ≤ measured L’n,w = 46 dB Proof of the footfall sound is thereby provided. Remarks regarding the calculation example Since the scientifically proven calculation described here differs from the requirements of DIN 4109, the proof for the separating ceiling must be rendered by means of a construction measurement. Simplified in-situ correction: for the calculation, the lab values L’n,w and R’w of the direct transmission are converted to match the construction situation by means of the structure-borne sound resounding period of the ceiling in the lab, Ts,lab, and at the construction site, Ts,situ. The effect of the in-situ correction (measured examples from the vibro-acoustics research project) is not considered in this calculation example; it results in a change of the calculated R’w or L’n,w values of an averaged ± 1 to 2 dB. L’n,w = 10log(10 0,1×38 + 100,1×13,9 + 100,1×14,1 + 100,1×31,8 + 100,1×37,0 + 100,1×16,9 + 100,1×22,1 + 100,1×31,8 + 100,1×37,0 ) = 43.0 dB 2 R’Dd = R’situ = R’lab – 10lg(Ts,situ /Ts,lab) or L’n,Dd = L’n,situ = L’n,lab + 10lg(Ts,situ /Ts,lab) 7 8
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