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Spécial “ Noise at work 2007 ”
Acoustique
&
Techniques n° 49
Acoustical evaluation and planning of offices
The overall sound power level LWA,wp of one workplace is
calculated as the energetic summation according to:
L
WA,wp
= L
WA,equipment
(+) L
WA,speech
=
{47 (+) 49} dB(A) = 52 dB(A)
(5)
Determination for criterion 3 (continuous noise load)
The above calculated noise power level L
WA,wp
inside the
office results in an average value of the background level
Lb according to following relation. The correction values
are related to the area per workplace, ceiling type and
noise screens.
L
b
= L
WA,wp
+ dLl
ayout
+ dL
screen
(6)
The influence of suspended ceilings with absorbing
characteristics and the average area size per workplace
is show in the following diagram.
The background level also depend considerably on
application of absorbing noise sceens. For open- plan
offices with noise screens of approximately 2 m height the
correction value dL
screen
is given in the following table.
Noise screen
(2 m height)
Ceiling
Reflective Absorbent
Reflective
0
-2
Absorbent
-1
-4
Table 4 : dLscreen for estimation of the background level Lb
In the example it is not intended to use noise screens
at first and the ceiling should be designed reflective.
In this case the following values for the background level
results:
L
b
= (52 + 0 + 0) dB(A) = 52 dB(A)
(7)
With absorbent ceiling, but without screens follows:
L
b
= (52 - 2 + 0) dB(A) = 50 dB(A)
(8)
With absorbent ceiling and absorbent
noise screens following level is
achievable:
L
b
= (52 - 2 - 4) dB(A) = 46 dB(A) (9)
Determination for criterion 2
(Annoyance caused by speech)
The two following pictures show
the necessary distance between
workplaces of different functional
groups, so that communication
noise does not cause unacceptable
annoyance. The calculations of these
diagrams take place for a sound
power level of speech of 65 dB(A) and
the condition, that the sound pressure
level caused by speech is 5 dB below
the background level.
The results for the floor size of 567 m² are :
Fig. 2: Effect of area per working place on the background level for absorbent ceilings
When reading the diagram figure 2 one has to bear in mind, that it shows
the change in the level at a workplace that has been regarded to be in 1m
distance to “its” source itself. The effect on the sound level caused by a ceiling
with absorbing characteristics is bigger between different workplaces.
Fig. 3: Determination of the necessary distance between different functional groups, so that communication
noise does not cause unacceptable annoyance (with reflective and with absorbent ceiling)