Open office acoustical design - multi-dimensional case studies

1. Open office acoustic
design
multi-dimensional case studies
ICA2007MADRID - F. KRAJCARZ Slide n°1

2. Contradictory aims
To be understood when needed
and
Conversations to remain confidential when
needed
and
Background noise as low as possible
ICA2007MADRID - F. KRAJCARZ Slide n°2

3. Scale of understanding based
on S/N ratio
ICA2007MADRID - F. KRAJCARZ Slide n°3

4. Very good intelligibility
Too low an ambient
noise level
ICA2007MADRID - F. KRAJCARZ Slide n°4

5. Very poor intelligibility
Too high an
ambient noise level
or
too low a signal
ICA2007MADRID - F. KRAJCARZ Slide n°5

6. An adapted signal-to-noise ratio
« normal-low »
voice : confidential
« normal-high»
voice : good
comprehension
ICA2007MADRID - F. KRAJCARZ Slide n°6

7. Managing intelligibility : two
complementary aims
Sufficient ambient noise (masking) but not too
much (long-term tiredness)
and
Signal-to-noise ratio allowing good or poor
intelligibility, without any special effort
ICA2007MADRID - F. KRAJCARZ Slide n°7

8. Parameters
Ambient noise :
number of noise sources
mean distance between sources
reverberation of the room
Signal :
sound power level of human voice
distance between speaker and listener
reverberating nature of the closest walls
screens
ICA2007MADRID - F. KRAJCARZ Slide n°8

9. Sound power level of human
voice
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz dB(A)
ICA2007MADRID - F. KRAJCARZ Slide n°9
80
77,5
75
72,5
70
67,5
65
62,5
60
57,5
55
52,5
50
47,5
45
42,5
40
Lw dB Lin

10. Tessiture
ICA2007MADRID - F. KRAJCARZ Slide n°10

11. Computer modelling : AcousPropa®,
developed by Gamba Acoustique & Associés
diffuse reflection on walls
diffraction on the edges of obstacles
calculation in octave bands
signal S, noise N and S/N ratio
ICA2007MADRID - F. KRAJCARZ Slide n°11

12. Example of modelisation
Room : 28 m x
15 m x 2.7 m
Screens height
: 1.5 m
54 noise
sources (18
« on »)
ICA2007MADRID - F. KRAJCARZ Slide n°12

13. Noise map – reverberant ceiling
Reverberant
ceiling
No screens
18 noise
sources « on »
About 64
dB(A)
everywhere
ICA2007MADRID - F. KRAJCARZ Slide n°13

14. Noise map – absorbent ceiling
Absorbent
ceiling
No screens
18 noise
sources « on »
55 to 58 dB(A)
ICA2007MADRID - F. KRAJCARZ Slide n°14

15. Noise map – absorbent ceiling
+ screens
Absorbent
ceiling
Screens
18 noise
sources « on »
53 to 55 dB(A)
ICA2007MADRID - F. KRAJCARZ Slide n°15

16. Signal map – reverberant
Reverberant
ceiling
No screens
1 signal source
« on »
ceiling
55 dB(A) at 2m
ICA2007MADRID - F. KRAJCARZ Slide n°16

17. Signal map – absorbent ceiling
Absorbent
ceiling
No screens
1 signal source
« on »
51 dB(A) at 2m
ICA2007MADRID - F. KRAJCARZ Slide n°17

18. Signal map – absorbent ceiling
+ screens
Absorbent
ceiling
Screens
18 noise
sources « on »
ICA2007MADRID - F. KRAJCARZ Slide n°18

19. S/N – reverberant ceiling
ICA2007MADRID - F. KRAJCARZ Slide n°19

20. S/N – absorbent ceiling
ICA2007MADRID - F. KRAJCARZ Slide n°20

21. S/N – absorbent ceiling +
screens
ICA2007MADRID - F. KRAJCARZ Slide n°21

22. Conclusion
Acoustic criteria S/N ratio in dB(A)
easy to use (calculation and measuring)
sufficient in open offices
Computer modelling
allow the layout of work stations, height of
screens, absorption coefficients, noise of the
technical equipment to be optimised in order
to achieve best intelligibility and
confidentiality.
ICA2007MADRID - F. KRAJCARZ Slide n°22

23. Thanks for your attention
ICA2007MADRID - F. KRAJCARZ Slide n°23