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126/10/2012Environmental Correction Factor26/10/2012Environmental Correction Factor1 Environmental correction factor K 2

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226/10/2012Environmental Correction Factor2 SPL vs distance from sound source Environmental correction factor K 2 K 2, also named DLf, Is the difference between the total SPL value and the free- field SPL value 26/10/2012Environmental Correction Factor

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326/10/2012Environmental Correction Factor3 We can compute K2 making the differnce between the formulas of the semireverberant sound field and of the free field: This formula provides the theoretical K 2 value Environmental correction factor K 2 Enveloping surfaces area = 2 d 2 Q=2 (source in a reflecting plane) 26/10/2012Environmental Correction Factor

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426/10/2012Environmental Correction Factor4 Experimental results

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526/10/2012Environmental Correction Factor5 These buildings are wide, but not tall Typical packaging workshops

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626/10/2012Environmental Correction Factor6 These buildings are wide, but not tall Typical packaging workshops

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726/10/2012Environmental Correction Factor7 An omnidirectional sound source (dodechaedron, Q=1) is employed Measurement of sound level vs distance S.L.M. Dodechaedron

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826/10/2012Environmental Correction Factor8 The experimental chart obtained looks as this one: Measurement of sound level vs distance

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926/10/2012Environmental Correction Factor9 Comparison with the theoretical curve Measurement of sound level vs distance Here the experimental SPL is significantly larger than the theoretical one Here instead it is smaller

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1026/10/2012Environmental Correction Factor10 The same happens in other similar buildings… Measurement of sound level vs distance

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1126/10/2012Environmental Correction Factor11 K 2 value vs distance

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1226/10/2012Environmental Correction Factor12 K 2 at teh workplace (surface S)

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1326/10/2012Environmental Correction Factor13 Results of the experiments In many industrial buildings large and short the envioronmental effect measured at the workplace is much larger than what theory predicts Often the owner of the factory acts against the supplier of machinery, in the wrong assumption that they are too noisy, whilst the cause of the high SPL value is mostly due to the building, and not to the machines This can be ascertainled only performing a direct measurmenet of the enviornmental correction factor K2 at the workplace Whenever K2 is very large, it can be expected that the SPL will reduce significantly thanks to an enviromental treatment based on sound absorption

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1426/10/2012Environmental Correction Factor14 K 2 estimation based on a new empirical formula

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1526/10/2012Environmental Correction Factor15 The Farina/Fornari Formula The formula was obtained by fitting the experimetal results measured in dozens of industrial workshops: In which T is the reverberation time, H is the room height and the terms within brackets at denominator represents an apparent volume of the large, short building

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1626/10/2012Environmental Correction Factor16 Verification of the new formula

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1726/10/2012Environmental Correction Factor17 Evaluation of effectiveness of room treatment The Farina/formari formula allows for easy assessment of the effectiveness of a room treatment For example, lets consider a building with these data: We now compute the value of K2 twice, before and after the room treatment, employing the Farina/Fornari formula.

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1826/10/2012Environmental Correction Factor04/11/2010Il Fattore di Correzione Ambientale18 Evaluation of effectiveness of room treatment The Farina/Fornari formula shows a relevant sound reduction due to room absorption treatment: at 10m we get a reduction of 5.5 dB(A) instead of 1.7 dB(A) as forecasted by the Sabines formula

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1926/10/2012Environmental Correction Factor19 Conclusions Employing the traditional formula for the environmental correction factor causes significant errors in large and short buildings, as most factories are. Nowadays the new EN 415-9:2009 standard allows for correct experimental extimation of the true value of the environmental correction factor The direct measurement of K 2 is easy and straightforward Alternatively, K 2. can be estimated quite accurately thanks to the Farina/Fornari formula In these buildings, often an absorption treatment produces much better results than what predicted by the traditional formulation

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