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ICA2007MADRID - F. KRAJCARZ Slide n°1
Open office acoustic design
multi-dimensional case studies
ICA2007MADRID - F. KRAJCARZ Slide n°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°3
Scale of understanding based on S/N ratio
ICA2007MADRID - F. KRAJCARZ Slide n°4
Very good intelligibility
Too low an ambient noise level
ICA2007MADRID - F. KRAJCARZ Slide n°5
Very poor intelligibility
Too high an ambient noise level
or
too low a signal
ICA2007MADRID - F. KRAJCARZ Slide n°6
An adapted signal-to-noise ratio
« normal-low » voice : confidential
« normal-high» voice : good comprehension
ICA2007MADRID - F. KRAJCARZ Slide n°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°8
ParametersAmbient noise :
number of noise sourcesmean distance between sourcesreverberation of the room
Signal :
sound power level of human voicedistance between speaker and listenerreverberating nature of the closest wallsscreens
ICA2007MADRID - F. KRAJCARZ Slide n°9
Sound power level of human voice
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz dB(A)40
42,545
47,550
52,555
57,560
62,565
67,570
72,575
77,580
Lw dB Lin
ICA2007MADRID - F. KRAJCARZ Slide n°10
Tessiture
ICA2007MADRID - F. KRAJCARZ Slide n°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°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°13
Noise map – reverberant ceiling
Reverberant ceiling
No screens
18 noise sources « on »
About 64 dB(A)
everywhere
ICA2007MADRID - F. KRAJCARZ Slide n°14
Noise map – absorbent ceiling
Absorbent ceiling
No screens
18 noise sources « on »
55 to 58 dB(A)
ICA2007MADRID - F. KRAJCARZ Slide n°15
Noise map – absorbent ceiling + screens
Absorbent ceiling
Screens
18 noise sources « on »
53 to 55 dB(A)
ICA2007MADRID - F. KRAJCARZ Slide n°16
Reverberant ceiling
No screens
1 signal source « on »
Signal map – reverberant ceiling
55 dB(A) at 2m
ICA2007MADRID - F. KRAJCARZ Slide n°17
Signal map – absorbent ceiling
Absorbent ceiling
No screens
1 signal source « on »
51 dB(A) at 2m
ICA2007MADRID - F. KRAJCARZ Slide n°18
Signal map – absorbent ceiling + screens
Absorbent ceiling
Screens
18 noise sources « on »
ICA2007MADRID - F. KRAJCARZ Slide n°19
S/N – reverberant ceiling
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S/N – absorbent ceiling
ICA2007MADRID - F. KRAJCARZ Slide n°21
S/N – absorbent ceiling + screens
ICA2007MADRID - F. KRAJCARZ Slide n°22
ConclusionAcoustic 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°23
Thanks for your attention
