126/10/2012 Environmental Correction Factor26/10/2012 Environmental Correction Factor 1

Environmental correction factor KEnvironmental correction factor K22

226/10/2012 Environmental Correction Factor 2

SPL vs distance from sound source

Environmental correction factor K2

K2 , also named DLf,Is the difference between the total SPL value and the free-

field SPL value

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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

Environmental correction factor K2

222 d4

Qlg10

A

4

d4

Qlg10K

V16.0

'ST41lg10 60

AQ

d441lg10K

2

2

Enveloping surface’s area = 2d2

Q=2 (source in a reflecting plane)

A

'S41lg10

26/10/2012 Environmental Correction Factor

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Experimental resultsExperimental results

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These buildings are wide, but not tall

Typical packaging workshops

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These buildings are wide, but not tall

Typical packaging workshops

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An omnidirectional sound source (dodechaedron, Q=1) is employed

Measurement of sound level vs distance

S.L.M.Dodechaedron

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The experimental chart obtained looks as this one:

Measurement of sound level vs distance

Thessaloniki - Livello sonoro in funzione della distanza - Lw = 100 dB(A)

60

65

70

75

80

85

90

95

1 10 100

distanza (m)

Liv

ello

so

no

ro (

dB

A)

Lsperim Ldir

K factor

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Comparison with the theoretical curve

Measurement of sound level vs distance

Thessaloniki - Livello sonoro in funzione della distanza - Lw = 100 dB(A)

70

75

80

85

90

95

1 10 100

distanza (m)

Liv

ello

so

no

ro (

dB

A)

Lsperim Lteor

Here the experimental SPL is significantly larger than the theoretical

one Here instead it is smaller

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The same happens in other similar buildings…Measurement of sound level vs distance

Thessaloniki - SPL decay with distance

70

75

80

85

90

95

1 10 100

distance (m)

SP

L (

dB

A)

Lsperim

Lsabine

Pelfort - SPL decay with distance

70

75

80

85

90

95

1 10 100

distance (m)

SP

L (

dB

A)

Lsperim

Lsabine

Patrasso - SPL decay with distance

70

75

80

85

90

95

1 10 100

distance (m)

SP

L (

dB

A)

Lsperim

Lsabine

Fredericia - SPL decay with distance

70

75

80

85

90

95

1 10 100

distance (m)

SP

L (

dB

A)

Lsperim

Lsabine

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K2 value vs distance

0

2

4

6

8

10

12

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K sper

K sab

0

2

4

6

8

10

12

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K sper

K sab

0

2

4

6

8

10

12

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K sper

K sab

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K-sper

K Sab

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K2 at teh workplace (surface S’)

0

0.5

1

1.5

2

2.5

3

Thessaloniki Pelfort Patrasso Fredericia

K-F

act

or

(dB

A)

Ksperim (dBA)

KSabine (dBA)

Nome V (m3) h (m) Tmed (s) Ksperim (dBA) KSabine (dBA) Thessaloniki 48836 8.3 2.60 2.40 0.48 Pelfort 72000 11.92 2.45 1.45 0.48 Patrasso 32000 8.0 3.10 2.75 0.51 Fredericia 27575 7.62 0.81 1.45 0.40

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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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KK22 estimation based on a new estimation based on a new

empirical formulaempirical formula

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The Farina/Fornari Formula

• The formula was obtained by fitting the experimetal results measured in dozens of industrial workshops:

27.0

37.0

2

teor

d2HT596.1

HT64.516.0

d2T41lg10K

'SHT596.1

HT64.516.0

'ST41lg10K

7.037.0

teor

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

0

2

4

6

8

10

12

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K sper

K teor

K sab

0

2

4

6

8

10

12

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K sper

K teor

K sab

0

2

4

6

8

10

12

14

1 10 100

distanza (m)

K-f

acto

r (d

B)

K sper

K teor

K sab

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

1 10 100

distanza (m)

K-f

act

or

(dB

)sperimentale

formula

Sabine

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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, let’s 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.

Parametro Valore u. di misura Volume Totale V 70.000 m3 Altezza media h 7 m Tempo di riverbero iniziale 3 s Tempo di riverbero trattato 0.7 s

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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 Sabine’s formula

Riduzione del livello sonoro totale

0

1

2

3

4

5

6

7

8

9

1 10 100

Distanza (m)

dB Dl,semiriverberante

DL,Farina/Fornari

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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 415-9:2009 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