Environmental correction factor K2

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Environmental correction factor K2
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Environmental correction factor K2
SPL vs distance from sound source
26/10/2012
Environmental Correction Factor
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Environmental correction factor K2
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 K2 value
Q2 (source in a reflecting plane)
26/10/2012
Environmental Correction Factor
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Experimental results
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Typical packaging workshops
These buildings are wide, but not tall
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Typical packaging workshops
These buildings are wide, but not tall
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Measurement of sound level vs distance
An omnidirectional sound source (dodechaedron,
Q1) is employed
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Measurement of sound level vs distance
The experimental chart obtained looks as this one
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Measurement of sound level vs distance
Comparison with the theoretical curve
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Measurement of sound level vs distance
The same happens in other similar buildings
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K2 value vs distance
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K2 at teh workplace (surface S)
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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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K2 estimation based on a new empirical formula
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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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Verification of the new formula
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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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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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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 415-92009 standard allows
  for correct experimental extimation of the true
  value of the environmental correction factor
• The direct measurement of K2 is easy and
  straightforward
• Alternatively, K2. 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