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Environmental correction factor K2

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Title: Acustica Ambienti Chiusi Author: armelloni Last modified by: farina Created Date: 9/16/2003 10:20:39 AM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: Environmental correction factor K2


1
Environmental correction factor K2
2
Environmental correction factor K2
SPL vs distance from sound source
26/10/2012
Environmental Correction Factor
3
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
4
Experimental results
5
Typical packaging workshops
These buildings are wide, but not tall
6
Typical packaging workshops
These buildings are wide, but not tall
7
Measurement of sound level vs distance
An omnidirectional sound source (dodechaedron,
Q1) is employed
8
Measurement of sound level vs distance
The experimental chart obtained looks as this one
9
Measurement of sound level vs distance
Comparison with the theoretical curve
10
Measurement of sound level vs distance
The same happens in other similar buildings
11
K2 value vs distance
12
K2 at teh workplace (surface S)
13
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

14
K2 estimation based on a new empirical formula
15
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
16
Verification of the new formula
17
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.

18
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

19
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
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