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Spécial “ Noise at work 2007 ”
31
Acoustique
&
Techniques n° 49
Acoustical evaluation and planning of offices
- a necessary distance of 12 m when the background level
is 52 dB(A) (case with absorbent ceiling but without noise
screens)
- a necessary distance of 8 m when a background level
is 50 dB(A) (case with absorbent ceiling but without noise
screens)
If an absorbent ceiling and additionally absorbent noise
screens are present, the background level drops to 46
dB(A). In that case the necessary distance can only be
determined with the inclusion of the reduction of the
communication noise from other functional groups,
caused by the absorbent noise screens. For this purpose
the following diagram can be used:
For distances of 4 to 5 meters between workplaces of
different functional groups, which are present in the given
example, follows a reduction of 8 dB, if absorbent ceilings
and noise screens of 2,2 meters height are present.
This additional reduction barely reach the requirements.
To verify the results with diagram 3 the background level
can be risen by 8 dB up to 54 dB(A) which results in a
necessary distance of 4 to 5 meters with a background
level of 46 dB(A) (case with absorbent ceiling and absorbent
noise screens)
Assessment without acoustical measures
The distance c between the functional groups is 4 m, the
distance d is 5,5 m (figure 1). The criterion 2 (Annoyance
caused by speech) is not fulfilled with the original layout
without acoustical measures, because the minimum
distance should be 12 m. In accordance to the background
noise level of 52 dB(A), the workplaces would have to be
classified as “unfavourable”.
Measures for improvement
A room setup with an absorbent
ceiling is insufficient on itself. The
workplaces should have a distance
of at least 8 m in order to fulfil
criterion 2 (Annoyance caused
by speech). This however is not
viable.
With an additional arrangement of
the room by placing absorbent noise
screens (see figure 5) between
the various functional groups, the
planned distances of 4 to 5 meters
between the workplaces will be
acceptable according to criterion
2 (Annoyance caused by speech).
Overall, the workplaces with the
described acoustic measures bases
on the estimated background noise of 46 dB(A) would be
classified as «acceptable» in accordance with table 1.
Open-plan offices in the best case are able to reach the
acoustical qualification «well».
Fig. 4: Level mitigation by a noise screen (room with absorbent ceiling)
Fig. 5 : Acoustic «isolation» of several functional groups with noise screens