Les réponses impulsionnelles directionnelles: évaluation et application dans le cadre de l'acoustique des salles

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28/2/2007 ABAV Brugge 2007 1

Determination of directional

echograms and application in room

acoustics

J.J. Embrechts, N. Werner and F. Duthoit

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source

listener

A diagram showing the

distribution of the acoustical energy at the receiver, as a function of time arrival.

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Echogram :

applications in room acoustics

Room acoustics

parameters

:

-T30, EDT - SPL - C80, D50 - …

Room impulse response

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28/2/2007 ABAV Brugge 2007 4 Y X ϕ

Ω

d

t

h

SR

(

θ

,

φ

,

)

A diagram showing the distribution of the acoustical energy at the receiver, as a function of time arrival,

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28/2/2007 ABAV Brugge 2007 5

source

listener

Directional echogram :

computation

Y Z X ϕ θ Ω d 67 5 22 5 0 -67 5 -22 5.

The directional echograms are evaluated by ray-tracing, at each listener’s position.

The 3D space around the listener’s head is divided into 26 solid angles, simulating 26 directional microphones.

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ABAV Brugge 2007

Directional echograms :

computation in two «

academic

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Example 1 : Room A

(

ref. Hodgson, JASA, 89(2), 1991

)

X

Z

Y

Source

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d=1

S R direct sound

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d=0

S R direct sound

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d=0

S

R

Room A : Directional echograms at one receiver position, 5m away from the source.

S

R

direct

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Example 2 : Room B

(

ref. Hodgson, JASA, 89(2), 1991

)

X

Z

Y

Source

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d=1

S R direct sound T30=4.3s

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d=0

direct sound S R T30=16.4s

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d=0

direct S R S R T30=4.3s T30=16.4s

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d=0

S R

d=1

S R T30=4.3s T30=16.4s

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d=0

S

R

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Conclusion of the analysis

of two «

academic

» problems

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Directional echograms :

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Project

:

Renovation of an ancient horse-

riding school into a cultural

polyvalent hall.

Théâtre du Grand Manège

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Project : Room B

(ref. Hodgson, JASA)

X

Z

Y

Source

Long disproportionate

room

-55m x 110m x 5.5m -absorption coefficient of all faces : 0.068 -scattering coefficient : d=0 or d=1

Seats

absorbing roof

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28/2/2007 ABAV Brugge 2007 23 S R T30 = 5.6s EDT=1.4s

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S

R

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S

R

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28/2/2007 ABAV Brugge 2007 S R S R

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Project :

Renovation of an ancient

horse-riding school into a

cultural polyvalent hall.

Théâtre du Grand Manège

(Namur)

First acoustical treatment :

Absorbent and diffusing surfaces on

the left wall

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S

R

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28/2/2007 ABAV Brugge 2007 29 S R S R before treatment : T30=5.6s after treatment : T30=1.9s

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Théâtre du Grand Manège

(Namur)

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S

R

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28/2/2007 ABAV Brugge 2007 33 S R S R horizontal audience : T30=6.2s

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Conclusions

-Directional echograms can give original information in non-diffuse acoustical fields. -They are particularly useful in the detection of potential flutter echos, lack of diffusivity and asymmetrical distribution of absorption. -T

hey can explain significant differences between T30

and EDT, as a result of nonlinear energy decays. -T

hey can suggest

optimal placement of absorbent